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Alexander Dubček University of Trenčín

Izhevsk State Technical University

Publishing House: Alexander Dubček University of Trenčín

(The international scientific journal founded by two universities from Slovak Republic and Russian Federation) This journal originated with kindly support of Ministry of Education of the Slovak Republic

Editorial Office Študentská 1, 911 50 Trenčín, Tel.: 032/7 400 279, 032/7 400 277 [email protected], [email protected]

Honorary Editors Miroslav Mečár, Assoc. prof., Ing., PhD. rector, Alexander Dubček University of Trenčín, Slovak Republic Jakimovič Boris Anatoľjevič, Prof., DrSc., rector, Izhevsk State Technical University, Russian Federation

Editor-in-Chief Miroslav Mečár, Assoc. prof., Ing., PhD., Alexander Dubček University of Trenčín

Science Editor Dubovská Rozmarína, Prof. Ing., DrSc., Alexander Dubček University of Trenčín

Members Alexander Dubček University of Trenčín Slovak Republic

Alexy Július, Prof. Ing., PhD. Gulášová Ivica, Assoc.prof., PhDr., PhD. Jóna Eugen, Prof. Ing., DrSc. Letko Ivan, Prof. Ing., PhD. Maňas Pavel, Assoc.prof., Ing., PhD. Mečár Miroslav, Assoc.prof., Ing., PhD. Melník Milan, Prof. Ing., DrSc. Obmaščík Michal, Prof. Ing., PhD. Zgodavová Kristína, Prof. Ing., PhD.

Izhevsk State Technical University Russian Federation

Jakimovič Boris Anatoľjevič, Prof., DrSc. Alijev Ali Vejsovič, Prof., DrSc. Turygin Jurij Vasiľjevič, Prof., DrSc. Ščenjatskij Aleksej Valerjevič, Prof., DrSc. Kuznecov Andrej Leonidovič, Prof., DrSc. Fiľkin Nikolaj Michajlovič, Prof., DrSc. Sivcev Nikolaj Sergejevič, Prof., DrSc. Senilov Michail Andrejevič, Prof., DrSc. Klekovkin Viktor Sergejevič, Prof., DrSc. Trubačev Jevgenij Semenovič, Prof., DrSc.

Redaction Bodorová Janka, Mgr.

Publishing House Alexander Dubček University of Trenčín, Študentská 2, 911 50 Trenčín

Graphic Design 3z SOLUTIONS - Zuzana Slezáková, www.3zs.sk

Technical Information © 2008 All rights reserved. Alexander Dubček University of Trenčín, Slovak Republic University Review Vol. 2, No. 3 Trenčín: Alexander Dubček University of Trenčín 2008, 90 p. ISSN 1337-6047 EV 2579/08

contents 3

Contributors

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Dean´s Foreword

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Carbon Nanotubes In Electronics S. Roth, V. Skakalova

An Analysis of Postbuckling Frequency Change of Beam Structures Using Finite Elements Method S. Isic, V. Dolecek, A.Voloder

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Intelligent Mechatronical System Using Repulsive Force Produced by Permannet Magnets M. Kosek, T. Mikolanda, A. Richter, P. Skop

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Evaulation And Future The Ulimate Limit State Design in Geomechanics P. Koudelka

Contactless Angle Transducer Dedicated For DC Micromotor M. Bodnicki, H. J. Hawłas

Tubular Metal Powder Permeable Materials With Anisotropic Structure And Their Applications V. Lapkovsky, V. Mironov, V. Zemchenkov, I. Boyko

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Rewiev of Destructive Methods of Testing of The Cement Paste And Concrete

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Properties And Quality of The Surface of Iron-Copper Powder Details

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Microstructure And Mechanical Properties of Poly(Vinyl Alcohol)-Plaster Composites

P. Padevět

V. Mironov, I. Boyko, V. Lapkovsky

H.F. El-Maghraby, O. Gedeon, A.A. Khalil

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Investigations of Microstructure of The Forging Die After Using – A Case Study J. Jasiński, G. Walczak, K. Kaczmarek, J. P. Jasiński

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Mechanica Load And Microstructure of Discharge Jet For Compresion Ignition Engine J. Jasiński, G. Walczak, K. Kaczmarek, J. P. Jasiński

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Neural Networks Modeling Carbonizing Proces In Fluidized Bed M. Szota, J. Jasinski

The Study of Microstructure of Precipitation-Strengthening HSLA Steel With Copper Addition P. Wieczorek, J. Lis, A. K. Lis

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Hot Ductility of Low Carbon Steel (S235JR)

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Evaluation of Microstructure of Nickel Superalloy Inconel 792-5A After Long Term Exploitation

A. K. Lis, N. Wolańska, C. Kolan

Z. Jonšta, P. Jonšta, V. Vodárek, K. Mazanec

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Rim Stress Distribution of Thin-Rimmed Gear

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Mechanical Design of Thermoplastic Shells of Small Wastewater Treatment Systems

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Platic Forming of Ecap Processed En Aw 6082 Aluminum Alloy

G. Marunić

O. Šuba, J. Jurčiová

M. Greger, L. Kander, B. Kuřetová

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Contributors

S. Roth, Max Planck Institute for Solid State Research, Stuttgart, Germany, Sineurop Nanotech GmbH, Stuttgart, Germany e-mail: [email protected] V. Skakalova, Max Planck Institute for Solid State Research, Stuttgart, Germany, Danubia Nanotech s.r.o., Bratislava, Slovakia

S. Isic, Faculty of Mechanical Engineering, Mostar, Bosnia and Herzegovina e-mail: [email protected] A.Voloder, V. Dolecek Faculty of Mechanical Engineering, Sarajevo, Bosnia and Herzegovina e-mail: [email protected] e-mail: [email protected]

M. Kosek, T. Mikolanda, A. Richter Technical University of Liberec, Liberec, Czech Republic e-mail: [email protected] e-mail: [email protected] e-mail: [email protected] P. Skop, Research Institute of Textile Machines, Liberec, Czech Republic e-mail: [email protected]

P. Koudelka, Institute of Theoretical and Applied Mechanicsm Prague, Czech Republic e-mail: [email protected]

M. Bodnicki, Institute of Micromechanics and Photonics, Warsaw University of Technology; Warszawa, Poland e-mail: [email protected] H. J. Hawłas, Institute of Precision and Biomedical Engineering, Warsaw University of Technology, Warszawa, Poland e-mail: [email protected]

G. Marunić University of Rijeka Faculty of Engineering, Rijeka, Croatia e-mail: [email protected]

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Contributors V. Lapkovsky, V. Mironov, I. Boyko Riga Technical University, Riga, Latvia e-mail: [email protected] e-mail: [email protected] e-mail: [email protected] V. Zemchenkov, TETA Ltd, Riga, Latvia e-mail: [email protected]

P. Padevět, CTU in Prague, Faculty of Civil Engineering, Prague, Czech Republic e-mail: [email protected]

H.F. El-Maghraby, O. Gedeon, Department of Glass and Ceramics, Institute of Chemical Technology, Prague, Czech Republic e-mail: [email protected] e-mail: [email protected] A.A. Khalil, Department of Refractories, Ceramics, and Building Materials, National Research Centre, Cairo, Egypt e-mail: [email protected]

J. Jasiński, G. Walczak, K. Kaczmarek, J. P. Jasiński Czestochowa University of Technology, Materials Engineering Institute, Biomaterials and Surface Layers Research Institute, Czestochowa, Poland e-mail: [email protected] e-mail: [email protected]

M. Szota, J. Jasinski Czestochowa University of Technology, Materials Engineering Institute, Czestochowa, Poland e-mail: [email protected]

Z. Jonšta, P. Jonšta, V. Vodárek, K. Mazanec VSB-Technical University of Ostrava, Ostrava-Poruba, Czech Republic e-mail: [email protected]

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P. Wieczorek, J. Lis, A. K. Lis Institute of Materials Engineering, Technical University of Czestochowa, Czestochowa, Poland e-mail: [email protected] e-mail: [email protected]

A. K. Lis, N. Wolańska, C. Kolan Czestochowa University of Technology, Częstochowa, Poland e-mail: [email protected] e-mail: [email protected] e-mail: [email protected]

O. Šuba, T. Bata University in Zlin, Faculty of Technology, Zlín, Czech Republic e-mail: [email protected] J. Jurčiová, Faculty of Industrial Technologies, Alexander Dubček University of Trenčín, Púchov, Slovak Republic e-mail: [email protected]

M. Greger, B. Kuřetová, VŠB-Technical University Ostrava, Ostrava, Czech Republic e-mail: [email protected] e-mail: barbora. [email protected] L. Kander, Material & Metallurgical Research Ltd, Ostrava, Czech Republic e-mail: [email protected]

Reviewers Prof. RNDr. Pavol Koštial, PhD. Prof. Ing. Vendelín Macho, DrSc. Prof. Ing. Eugen Jóna, DrSc.

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Prof. RNDr. Juraj Slabeycius, PhD. Prof. Ing. Ivan Letko, PhD.

dean´s foreword

prof. RNDr. Pavel Koštial, PhD.

T

he long-term cooperation between Polish and Slovak researchers in the field of machine design and materials engineering resulted in nine meetings heldin Poland and Slovakia since 1996 under the common name “Theoretical and Experimental Problems of Materials Engineering”. Czech researchers have been involved in organization of these conferences since 2003 and have been honoured by organization of the jubilee 10th meeting in Rožnov, 2005 (PiME05). Last conference was located in the beautiful spa region of the town Rajecké Teplice in Slovakia. The conference was organized by the Faculty of industrial technologies in Púchov, University of Alexander Dubček in Trenčín in the period August 25th - 28th 2008. The purpose of the conference is to present current results in materials engineering, chemistry and mechanics of materials, mechanics and design in applications. The conference topics : A. Physicaland chemical properties of materials, nanomaterials B. Mechanical properties of materials C. Experimental methods in materials engineering D. Mechanicsand computer simulation The first part of proceedings is oriented mainly in mechanics of materials, materials engineering and design.

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CARBON NANOTUBES IN ELECTRONICS

S. Roth, V. Skakalova

Abstract Carbon nanotubes have been discovered about 15 years ago. Meanwhile some 30 000 papers have been published on this topic and carbon nanotubes are often claimed to be the most promising material of the 21st century. This paper will give an introduction into the physical phenomena which can be studied in these materials (conductance quantisation, single-electron effects, ballistic transport, van Hove singularities, zero-gap semiconductor, bipolar transport, linear dispersion relation, degenerate sublattices ...). Carbon nanotubes will be discused with respect to their attractiveness for studies in fundamental physics as well as their perspectives for technological applications (carbon electronics, tube-transistors, sensors, interconnects, vias, nanoelectromechanical devices ...).

Key words carbon nanotubes

S

ome people claim that carbon nanotubes will be the most important material of the 21st century. The future will tell us whether this is true, but the past teaches that most predictions are wrong. In any case, carbon nanotubes

certainly are the most popular material of the present: Since their discovery in 1991 [1] some 20 000 publications have appeared and some 1000 patents have been filed. Fig. 1 shows the computer model of a carbon nanotube.

Fig. 1: Computer model of a single-walled carbon nanotube

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Carbon nanotubes are seamless tubes of graphitic monolayers, about 1 or 2 nanometers in diameter and up to several micrometers or even millimeters long. Depending on the diameter and on the details of seamless joining, the nanotubes are metallic or semiconducting. Because of the strong carbon-carbon bond and because of phase space arguments in narrow constrictions, there are only few scattering events in nanotubes and the conductivity is mainly ballistic, which for practical purposes means, for metallic nanotubes it is very high. The energy gap of semiconducting nanotubes can range from a few meV up to 1 eV. There are single-walled and multi-walled carbon nanotubes. Multi-walled nanotubes consist of up to 70 concentric tubes. For monographs on carbon nanotubes see Refs. [2-5]. If there are semiconducting nanotubes, it is tempting to make nanotube transistors. Several groups have prepared and investigated such transistors [6-11]. These transistors are expected to be smaller than silicon transistors, faster, and less energy-consuming. Fig. 2 shows a schematic diagram of a nanotube field-effect

transistor (TUBE-FET): A semiconducting singlewalled carbon nanotube is placed on the oxide layer of a doped silicon chip. Gold leads are applied by electron beam lithography as source and as drain contacts. Usually the nanotube is already p-doped from the purification process (which generally involves an oxidation step) or it gets p-doped by interaction with the gold leads (different work function between carbon and gold). Consequently the nanotube is conducting and the transistor is in the “on” state. To switch the transistor off, a voltage is applied between the nanotube and the doped silicon chip (which serves as a gate contact). The on-off ratio of such a transistor can be as large as 5 or 6 orders of magnitude and it has been shown that these nanotube transistors outperform the best silicon transistors also with respect to other parameter. Fig. 3 shows an AFM image of a single-walled carbon nanotubes placed over 4 gold leads prepared by electron beam lithography [12]. Any two of the gold leads can be used as the source and the drain contact of the fieldeffect transistor.

Fig. 2: Schematic diagram of nanotube field-effect transistor

Fig. 3: AFM image of a carbon nanotube laying over 4 gold leads prepared by electron beam lithography [12]

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Fig. 4: “All-carbon” transistor with nanotube not only as conducting channel but also with nanotube gate. The dielectric is a linker molecule at the T-junction. The device has been “synthesized by wet-chemical methods” and adsorbed on a silicon chip prior to the application of the lithographic gold leads [11]

Fig. 4 presents the “all-carbon” transistor, where the gate is also a carbon nanotube [11]. This transistor has been “synthesized by wetchemical methods”, and in principle it would allow for really nanometer-sized devices and extremely high integration density. Phaedon Avouris’ group at IBM has prepared a complimentary field-effect device consisting of a nanotube over tree gold electrodes and of which one part is p-doped and the other n-doped [13]. n-doping has been achieved by covering one part of the nanotube by a polymer film and exposing the other to ammonia, so that there the original p-doping is overcompensated (Fig. 5). Such a device can serve as a voltage inverter

(or as a logic NOT gate). An other way of saving space and going to higher integration densities is to put the transistors vertical and to use a wrap-around gate. Such transistors have been patented by Infineon and by Samsung. An artist’s view is shown in Fig. 6 [14]. Today we have quite a good understanding on how transistors can be made from individual nanotubes and on how individual nanotubes behave compared to silicon, but we lack a technique of selecting the wanted type of nanotubes and then positioning it in the right place. Developing a technology which could one day replace large scale integrated silicon circuits is an endeavour of decades, not of years.

Fig. 5: Voltage inverter consisting of a p-type and an n-type carbon nanotube field-effect transistor [13]

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Fig. 6: Vertical nanotube field-effect transistor with wrap-around gate electrode [14]

The limiting problem of today’s electronics is not the active elements (transistors), it is wiring. Wiring at all levels, from the cables between computer and peripherals down to interconnects between the transistors on a chip. A special challenge are VIAs (vertical interconnect access), connecting different layers on a chip. It is very difficult to pass high current densities through very thin wires of conventional metals because of surface and grain boundary scattering. In addition, such thin wires tend to decompose, releasing small metal particles which migrate around within the circuitry (electromigration). Because of the strong covalent bonds between carbon atoms, as compared to the rather week metallic bonds, there is much less electromigration from carbon nanotubes,

and the maximum current density in carbon nanotubes is by three orders of magnitude higher than in copper wires. Therefore several companies are working on VIAs based on carbon nanotubes. Fig. 7 shows the electronmicrograph of a multi-walled nanotube growing out of a hole etched into a silicon chip [15]. Experts believe that a hybrid technology - with active elements based on silicon and with interconnects based on carbon - could be ready within a few years. An “all-carbon” technology with metallic nanotubes connecting transistors from semiconducting nanotubes is a dream for a very far future. Yet, a disordered version of this dream has already been realized today: the transparent nanotube transistor.

Fig. 7: Multi-walled carbon nanotube growing out of a hole etched into a silicon chip, first step towards nanotube-based VIAs [15]

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Individual nanotubes are difficult to handle. But there are many applications in which large ensembles of nanotubes are used. This is particularly true for nanotube-polymer composites, i.e. for polymers filled with carbon nanotubes. Such filling might improve the electrical and mechanical properties of the polymers. Of course, polymers filled with larger particles do already exist (e.g. aluminium flakes, silver beats, or stainless steel fibres as conductive fillers, carbon fibres for mechanical reinforcement), and non-tubular nanoparticles have also been known for a long time as polymer fillers (carbon black for chemical purposes in car tires, carbon black as pigments, carbon black as conductive fillers). Conductive polymers can be used for dissipation of electrostatic charges, for electromagnetic shielding, and for electrical heating (of car seats or of outside mirrors). There are certain advantages if the fillers are thin and long (lower percolation threshold, so that less filler material is needed) and there are certain advantages if the filler particles are nanometer size (homogeneity down to nanometer scale as needed in ultrathin adhesive layers). Because of the low percolation threshold that can be obtained with nanotube filling, combined with nanoscale homogeneity, transparent conductive films can be made. These films can compete with ITO layers (indium-tin oxide), which is the standard material for transparent electrodes (needed in solar cells and in light

emitting devices). A very interesting example of the application of transparent nanotube networks is the flexible transparent nanotube transistor [16]. A photograph of such a transistor is shown in Fig. 8. and a schematic drawing in Fig. 9. The essential feature of this transistor is that there are two transparent nanotube layers, separated by a thin insulating layer of parylene. Both layers consist of a mixture of metallic and semiconducting nanotubes (Today only mixtures of nanotubes can be synthesized and there is no efficient way of separating them). For the lower layer the nanotube concentration is chosen such that the metallic nanotubes form a continuous network. This layer behaves like a metal and serves as the gate electrode of the transistor. In the upper nanotube layer the concentration of the tubes is only half as large. Now most metallic nanotubes do not touch and the network is only continuous if both metallic and semiconducting nanotubes are taken into account. This network behaves semiconductorlike and forms the conducting channel of the transistor. Actually, this layer can be considered as a random ensemble of individual semiconducting nanotubes, each connected by metallic nanotubes as local source and drain contacts. The works were realised under support of project Excgange Pragramme DAAD-MSSR (D/07/01257).

Gold Source-Drain Contacts

Parylene N (Insulating Layer)

Gold Contacts to the Gate

Rare Nanotube Network as Source-Drain Channel

Dense Nanotube Network as Gate Layer

Flexible PE substrate Fig. 8: Photograph of flexible transparent nanotube transistor [16]

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Fig. 9: Schematic drawing of flexible transparent nanotube transistor [16]

Literature 1. IIJIMA, S.: Helical microtubulus of graphitic carbon. Nature 354, 56-58 (1991). 2. EBBESEN, T.W. (Ed.): “Carbon Nanotubes - Preparation and Properties” CRC Press (1997). 3. DRESSELHAUS, M.S., DRESSELHAUS, G., AVOURIS, Ph. (Eds.) “Carbon Nanotubes” Springer (2000). 4. HARRIS, P.J.F.: “Carbon Nanotubes and Related Structures” Cambridge University Press (1999). 5. SAITO, R., DRESSELHAUS, G., DRESSELHAUS, M.S.: “Physical Properties of Carbon Nanotubes” Imperial College Press, London (1998). 6. TANS, S.J., VERSCHUEREN, A.R.M., DEKKER, C.: Room-temperature transistor based on a single carbon nanotube. Nature 393, 49–52 (1998). 7. H.W.C., POSTMA, T., TEEPEN, Z., YAO, M., GRIFONI, C. DEKKER,: Carbon nanotbe single-electron transistors at room temperature. Science 293, 76–79 (2001). 8. MARTEL, R., SCHMIDT, T., SHEA, H.R., HERTEL, T., AVOURIS, Ph.: Single- and multi-wall carbon nanotube field-effect transistors. Applied Physics Letters 73, 2447-2449 (1998). 9. HEINZE, S., TERSOFF, J., MARTEL, R., DERYCKE, V., APPENZELLER, J., AVOURIS, Ph.: Carbon nanotubes as Schottky barrier transistors. Physical Review Letters 89, 106801-1 -106801-4 (2002). 10. JAVEY, A., GUO, J., WANG, Q., LUNDSTROM, M., DAI, H.: Ballistic carbon nanotube field-effect transistors. Nature 424, 654–657 (2003). 11. CHIU, P.W., KAEMPGEN, M., ROTH, S.: Band-structure modulation in carbon nanotube T-junctions. Physical Review Letters 92, 246802-1 - 246802-4 (2004). 12. J. MUSTER, M. BURGHARD, S. ROTH, G.S. DUESBERG, E. HERNÁNDEZ, AND A. RUBIO. Scanning force microscopy characterization of individual carbon nanotubes on electrode arrays. Journal of Vacuum Science and Technology B 16, 2796 (1998). 13. AVOURIS, Ph., MARTEL, R., DERYCKE, V., APPENZELLER, J.: Carbon nanotube transistors and logic circuits, d 10598, USA, Physica B 323,6-14 (2002). 14. KREUPL, F., DUESBERG, G.S., GRAHAM, A.P., LIEBAU, M., UNGER, E., SEIDEL, R., PAMLER, W., HÖNLEIN, W.: “Carbon nanotubes in microelectronic applications”. In: Physics, Chemistry and Application of Nanostructures : Reviews and Short Notes to Nanomeeting 2003 Minsk, Belarus 20-23 May 2003. S.V. Gaponenko, V.S. Gurin (Eds.). World Scientific Pub Co Inc (2003/04) 15. KREUPL, F., GRAHAM, A.P., LIEBAU, M., DUESBERG, G.S., SEIDEL, R., UNGER, E.: IEDM Tech. Dig., pp. 683 - 686, December 2004, cond-mat/0412537. 16. ARTUKOVIC, E., KAEMPGEN, M., HECHT, D.S., ROTH, S., GRÜNER, G.: Transparent and flexible carbon nanotube transistors. Nano Letters 5, 757-760 (2005).

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AN ANALYSIS OF POSTBUCKLING FREQUENCY CHANGE OF BEAM STRUCTURES USING FINITE ELEMENTS METHOD

S. Isic, V. Dolecek, A.Voloder

Abstract This paper presents analysis of vibrations frequency of axially loaded beams in a postbuckling states, using finite elements method. Non-linear equation of motion takes into account up to third order terms of stiffness and stress stiffening. Non-linear equation of vibration is solved using direct integration methods and frequencies of vibration are calculated by transformation of the obtained solutions to frequency domain. According to assumption that beam buckles in the form of first buckling eigenmode, it is derived single non-linear differential equation of vibration, which is enough simple for analytical or numerical analysis. This equation gives results which agree well with solution obtained using direct integration methods of complete finite element equation of vibration. Obtained results shows increasing of the postbuckling frequency with increasing of axial force and initial displacement from straight-line position.

Key words beam, finite elements method, postbuckling, frequency

A

n analysis of eigenfrequencies of the small vibration of beam structures defines character of stability of the current equilibrium position [1]. For critical load, the lowest eigenfrequency becomes zero, and any small perturbation leads to buckling of a beam. For load greater than critical, linear analysis indicates imaginary value of the frequency. It is already known that beam structure has stable equilibrium postbuckling positions [2], and frequency should have real values. It is necessary to introduce non-linear analysis for its calculation. For analytic calculation of the frequency of buckled beam, perturbation method may be used [1]. It

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respectable mathematical problem for systems with many d.o.f-s, because of that, solutions exist for simplified beam models with two d.o.f. [4], [5]. Some numerical method must be used in the case of an analysis of complex systems. This paper presents analysis of vibrations frequency of beams in a postbuckling states using finite elements method. A non-linear equation of postbuckling vibration is derived taking into account higher order terms (up to third order) of a stiffness and stress stiffening. A non-linear equation of vibration is solved using direct integration methods and frequencies of vibration are calculated by transformation of the obtained

solutions from time to frequency domain. This is combination of two time consuming calculations, and to make it applicable some acceleration of the process should be used. According to assumption that beam buckles in the form of first buckling eigenmode, it is derived single non-linear differential equation of vibration, which is enough simple for analysis using analytical perturbation methods or method for numerical integration. This equation gives results which agree well with solution obtained using direct integration methods of complete finite element equation of vibration. A content of the spectrum and frequency change in postbuckling states of a beam is calculated for different values of axial force greater than critical, and also for different initial condition of a beam.

FINITE ELEMENTS ANALYSIS Equation of motion

beam looses stability, beam departs from initial straight-line position and vibrates around new buckled configuration. It is supposed that elastic properties of the system remain linear for this value of large displacements. Bended shape of the beam and axial displacements u of the elastic line caused by buckling are uniquely determined by lateral displacements w(s) measured in the natural coordinate system of the beam [2]. The beam is discretized on n standard Euler beam elements with two nodes and four d.o.f. in the element displacement vector {d}ei = {w1 w1,s w2 w2,s }T Using derivatives w1,s and w2,s as nodal displacements (which represent sine of slope angles) instead slope angles θ1 and θ2 allows usage of the same function of interpolation and shape function as in linear analysis [2].

Lets consider axially loaded beam as shown in the Fig. 1. Beam is loaded by axial force P which is constant in value and direction. When

Fig. 1: Buckled simple beam and beam finite element with large displacements

Considering third order polynomial interpolation function, displacement of arbitrary point could be calculated from nodal displacements as (1) where [N] are element shape matrix as in case of linear analysis of bending and stability [3].

Potential energy of deformation caused by beam bending may be calculated as (2) 2 where κ is curvature of the elastic line in natural coordinate system, and B is bending stiffness.

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Expanding (2) in power series (limiting third order), and inserting equation for displacement (1), we get the following expression for the deformation energy concentrated in the beam under bending

(3)

Variation of deformation energy is then given by (4) where matrix epresents element stiffness matrix [k]ei , known in linear analysis [3], and matrix [k1] is element matrix of nonlinear effects on beam stiffness, given by (5) Axial displacement ΔL of the end of beam, where acts axial force, is given by (6) where in power series expansion are used members up to forth power. Using (6) and inserting expression for interpolation of displacements (1), potential energy of the axial force may be written in the form (7) Variation of the potential energy of the axial force may be written as (8) where is stress stiffening matrix of the beam finite element [kσ]ei [3], and matrix [kσ]ei is matrix of nonlinear effects on stress stiffening of the beam with second order coefficients, given by (9) Because of small axial displacements and low vibration frequency, variation of kinetic energy T of the motion in the vertical direction is given by linear expression known from analysis of small vibration (10) where [m]ei is consistent mass matrix of the beam finite element [3]. An equation of motion of the beam is derived on the basis of Hamilton’s principle.

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(11) Supposing that displacement vector {D} receives arbitrary perturbation δ{D}, which vanishes at the boundaries of the time interval [t1, t2], equation of motion could be written in the form (12) where [M], [K], [Kσ], [K1] and [Kσ1] are matrices of the structural size, created by standard finite elements procedure from corresponding element matrices [m]ei, [k]ei, [ks]ei, [k1]ei and [kσ1]ei [3].

Direct integration of the equation of motion Equation (12) is solved by using implicit direct integration method. Starting from initial condition {D}(0), {D}(0) and chosen time step Δt, displacement vector {D}(i+1), is calculated from equation (13) This solution by direct integration method is time consuming, because et every time step i calculation of displacement requires additional subiterations. It may be very helpful if approximate solution exists which predicts nature of the solutions with acceptable accuracy. In this purpose, lets consider that {D}0 is buckling eigenvector, and b is chosen representative displacement (e.g. middle point displacement in the case of the simple beam). Buckling eigenvector then may be written as (14) where

is scaled by value of representative displacement b in {D} 0.

w/L w/L Fig. 2: Phase orbit of the beam middle point for different value of axial force

Considering displacement vector {D} in shape of buckling eigenvector [5, 6], and multiplying (12) by , we get one differential equation in the form (15)

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Equation of motion is now equation of one unknown variable b, and for it is neccessarry to calculate given matrix products only once, usung results of linear stability analysis. On the Fig. 2 are presented results of integration of the equation of motion (12) for middle point of the simple beam, obtained by using both equations (13) and (15). Results are given through phase plane of the point for two values of axial force and initial position in the buckled shape where middle point has displacement L/100. Following data are used: E = 210 [GPa], L = 0.34 [m], I = 0.216·10 -10 [m4], Δt = 0.0003 [s]. Results show that simplified equation (15) may be used for value of axial force lower then 1.05Pcr (which is also limit of accuracy of the equation of motion containing third order terms).

RESULTS DISCUSSION Fig. 3. presents content of frequency spectrum of postcritical vibration (a) and change of the base frequency for different value of axial force and initial displacement (b) given through ratio of postbuckling frequency and frequency of free vibrations. Frequencies are calculated applying Fourier Transform (FFT) to the solutions of equation (12). Zero frequency in the spectrrum shows existence of departure from initial straight-line equilibrium position, and first and second higher harmonics of base frequency show large displacement. Increasing of axial force causes increasing of the base frequency. Increasing of the initial displacement causes increasing of the frequency also, because of effects of nonlinear stiffness and stress stiffening terms in equation of motion.

Fig. 3: Frequency spectrum and frequency change of buckled simple beam

CONCLUSIONS Finite element analysis of posbuckling frequency change is presented. It is derived nonlinear equation of motion and solved using direct integration method. Frequency is calculated by FFT trans-formation of obtained numerical resultsin time domain. Significant decreasing of calculation efforts is obtained by simplified equation of motion, given by single nonlinear differential

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equation. Obtained results show slow increasing of base frequency with increasing of axial force and initial displacement from initial stright-line position, what points to stable equilibrium configuration of buckled beam.

Literature 1. THOMSEN, J.J.: “Vibration and Stability – Order&Chaos, Technical University of Denmark, Lyngby, 1994. 2. THOMPSON, J.M.T., HUNT, G.W.: A General Theory of Elastic Stability, John Wiley & Sons, 1973. 3. COOK, R., MALKUS, D.S., PLESHA, M.: ‘’Concepts and Application of Finite Element Analyses’’, John Willey & Sons, New York, 1988. 4. THOMSEN, J.J.: “Chaotic Dynamics of Partially Follower-Loaded Elastic Double Pendulum”, Journal of Sound and Vibration, Volume 188, Issue 3, Pages 385-405, October 1994. 5. ISIC, S., DOLECEK, V., KARABEGOVIC, I.: “Bifurcation Analysis of Elastic Systems Based on Frequency Spectrum of Large Vibrations“,The 17th International DAAAM Symposium “Intelligent Manufacturing & Automation: Focus on Mechatronics & Robotics”, Wien, Austria, 8-11th November 2006 6. ISIĆ, S., DOLEČEK, V., KARABEGOVIĆ, I.: “An Identification of Bifurcation Type Using Postcritical Motion Analysis “, Proceedings of 5th International Congress of Croatian Society of Mechanics, September, 21-23, 2006, Trogir/Split, Croatia, Pages 83-84.

INTELLIGENT MECHATRONICAL SYSTEM USING REPULSIVE FORCE PRODUCED BY PERMANNET MAGNETS

M. Kosek, T. Mikolanda, A. Richter, P. Skop

Abstract Two permanent magnets can be used for both the breaking of moving object and sensing its position. Such system design and analysis need the exact calculation of magnetic field. The robust computational method uses integral form of Biot-Savart Law working with coupled volume and surface currents derived from magnetization. Either the simplest assumption of uniform magnetization shows a good agreement between calculated flux density and experimental results, with an exception of the field near magnet edges. This assumption also allows the reliable calculation of repulsive force. The calculated dependence of axial and radial components of flux density on distance between magnets exhibits a maximum for suitable Hall probe position. Since the maximum position is different, the distance measurement is possible by using two Hall probes. The calculations give all data necessary for the design of controller that allows the correct operation of this simple but robust mechatronical system.

18

Key words retarding force, position sensor, magnetic force, permanent magnet, Hall probe

T

he advantage of mechatronical systems is that they connect both the mechanical acting part and electronic control. The system for mechanical breaking based on repulsive force permanent magnets contains both the parts in a very simple way. The magnetic flux due to the permanent magnets produces the force. Since its value depends on magnet position, it can be simultaneously used for device position measurement and control. The ideal measuring element is the Hall probe and the exact control can be realised by smart sensors or microprocessor controller. However, the most important property of the new solution is simplicity, reliability and robustness, since only two permanent magnets of simple ring shape are used. The use of permanent magnets for breaking force realisation is a new idea; therefore, there are practically no experiences with it. A simple and relatively cheap way is to model the device, estimate its parameters and simulate its action. The parallel simple experiments must be made in order to verify the models. The modelling of the system is a subject of this paper. The paper outlines basic theory, mentions the experiment, presents the results of numerical calculation, compares them with experiment and discusses future use.

THEORY The magnet is given very simply by its geometrical parameters and magnetization M that fully describes its magnetic properties. There are two basic ways how to calculate all the magnet effects. They can be derived by superposition either from elementary magnets of magnetic momentum MdV in the magnet volume or from the coupled elementary volume imdV and sur-

19

face jmdS currents that are derived from volume distribution of magnetization in the sample. In basic textbooks of electromagnetism there is a proof that the effect of coupled currents is equivalent to the action of magnetic dipoles. We have preferred the method of elementary coupled currents, since the (free) currents are used frequently in electrical engineering. The magnetic flux density B due to both the coupled currents is given by formula

(1)

where im and jm are coupled volume and surface current density, respectively, S and V are the surface and volume of the magnet, respectively, r is a position vector of the point, where the flux density B(r) is calculated, r0 is the position vector of surface and volume elements dS and dV, respectively. The formula requires numerical integration and can be used for the calculation of magnetic force as well as for the measured the Hall probe field dependence on the position of magnet. The magnetic force between two permanent magnets can be calculated at least by three methods: by the superposition of forces between elementary magnetic dipoles, the superposition of forces between elements of surface and volume coupled currents and by the superposition of forces, by which the field of one magnet acts on the elementary coupled currents of the second magnet. We preferred the third method because of its universality.

The fixed magnet produces the field. The formula for resulting force F for moving magnet at position r can be written as (2)

where B(r0) is the magnetic field at position r0 of surface and volume elements dS and dV, respectively, jm and im are coupled surface and volume current densities, respectively, S and V are the surface and volume of the moving magnet, respectively. In the simplest case we consider the uniform magnetisation, since it is the only value given by a producer. As a consequence, the coupled volume currents are zero and surface ones are of uniform density. The flux density and magnetic force should be calculated by numerical integration either for very simple magnet shape, cylinder or ring.

EXPERIMENT The commercial ring magnet used in preliminary experiments had geometrical dimensions: thickness of 4 mm, inner radius of 25 mm and outer one of 70 mm. The magnetization was 1.2 T, approximately. We have made measurement of the magnetic flux density and repulsive force. Both the experiments were made on fully automated apparatus. The measurement of magnetic field was made by commercial Hall probe instrument that is automatically moved in a plane parallel to

magnet main surface. Since the Hall probe dimensions are relatively large, the average value of magnetic flux density was measured, instead of the strict local value. A relatively low number of measured points were reached. The experiment with Hall probe for the measurement of magnet position was not realized yet. The repulsive force was measured by piezoelectric sensor and the position of moving magnet was scanned by a commercial LVDT (Linear Variable Differential Transformer). A high number of measured values were processed by standard statistical methods.

RESULTS The calculation of magnetic flux density and repulsive force was made by numerical integration in MATLAB. Since there were a large number of nested cycles, the computation time was relatively long, tens of minutes in complicated cases. Only typical results and comparison with experiment will be presented here. The comparison of calculated and measured magnetic field is in Fig. 1. The flux density is calculated across the magnet diameter at two distances: just on the magnet surface and at the distance 5 mm from it. Measured values are given by crosses. The calculated values were averaged in order to take into account final dimension of the sensing element. With except of a magnet edge, the agreement with experiment is good. The total coupled surface current is also shown in Fig. 1. Its value cannot be realised in practice, probably.

x [mm] x [mm] Fig. 1: Calculated and measured magnetic flux density

20

The dependence of total force between magnets on the distance between them is in Fig. 2. According to the experiment three magnets were considered. This choice is an optimum selection, as the calculations revealed. The total coupled surface current is very high – 12 kA. Comparison with experiment ... Brem = 1.3 T

Only a small part of experimental points, denoted by crosses, is used for comparison. The repulsive axial force has a relatively high value and there is a relatively good agreement with experiment. Nevertheless, small systematic deviation exists. Radial force ... Im 12 kA

700 600

Fz [N]

500 400 300 200 100 0 z [mm]

z [mm]

Fig. 2: Axial and radial forces between magnets and a comparison with experiment for axial force

The equilibrium for repulsive force is unstable. Any small deviation of the moving magnet from perfect axis position leads to the momentum that tries to rotate the magnet into the position of attractive force which has a minimum of potential energy. If the rotation is not possible, the radial force acts on the bar in the hole. The dependence of radial force of the deviation from equilibrium position is in the right hand part of Fig. 2. The force is not high in comparison with axial one, nevertheless its negative effects, for

instance the friction, should be taken into account in the design of the device. The measurement of radial force is difficult; therefore no comparison with experiment is presented. Hall probe positioned in fixed point can be used for the measurement of the distance between magnets. However, the flux density depends on the probe position. We have considered several positions of the probe in the upper plane of fixed magnet outside the external

Fig. 3: Dependence of flux density on distance between magnets for 2 positions of Hall probe

21

tunately, the maximums are not identical; the unambiguous distance can be obtained from both the components. For comparison, basic parameters for several probe position are summarised in Tab. 1 for several probe position xp from outer contour of fixed magnet in its upper plane. The second column shows the minimum distance that can be measured by radial probe. The total radial field change is in the third column. Analogically, the fourth column contains maximum distance that can be measured by axial probe and in the last column there is the corresponding probe sensitivity. The sensitivity decreases rapidly, as the distance of probe increases.

diameter. The Hall voltage is proportional to the magnetic flux density. The dependence of flux density (and Hall voltage) on the distance between magnets for near and far probe position is given in Fig 3. Both the curves, for axial (Bz) and radial (Bx) component of magnetic flux density, exhibit a maximum at some distance between magnets. The position of maximum is given by vertical lines in Fig. 3. Maximums are shifted to higher positions with increasing distance of the probe from magnet. Unfortunately, the probe sensitivity decreases dramatically. Since the curves have maximums, the two distances between magnets will be obtained from one Hall voltage for one component. Forxp [mm]

rmin [mm]

ΔBr [mT]

rmax [mm]

ΔBz [mT]

3

1.5

116

12

149

6

4

48

21

79

9

6

28

26

49

15

11

11.5

36

26

Tab. 1: Parameters of probes for distance measurement

DISCUSSION The outlined method needs only geometrical dimension of magnets and one material parameter, magnetization. If we take into account very simple inputs and no corrections, the agreement with experiment is good and can be used in technical praxis. The agreement can be improved if we refine the model. The most important neglect was the uniform magnetisation. The more correct magnetisation distribution can be assumed, while the calculations change only slightly. Unfortunately, there is not a simple and straightforward way how to find the correct distribution of magnetization. Method of trials and errors appears as the only one solution. We have used the model of coupled currents and integral formulae for the calculations. Usually the finite element method is preferred. Our approach has several advantages. The programming is relatively simple, the user has full check

at all steps of computation, and there are no problems with boundary conditions especially in infinity. All the quantities can be calculated at any given point and the accuracy can increase to any reasonable value. The only disadvantage is relatively long computation time, but the cluster can be used if necessary. The main advantage of the new solution is that the magnetic field is used for two purposes: creating a repulsive force and, simultaneously, a voltage that determines the distance between magnets. Both the quantities depend on distance nonlinearly. Furthermore, the correct value of distance needs both the components of flux density, axial and radial one. The precise calculation of force and Hall voltage characteristics for a given probe position, which was made by authors, can be used in the programming of the controller.

22

CONCLUSION The simple and exact method for complete analysis of mechatronic system based on application of repulsive force between permanent magnets was realized. Even the simplest assumption of uniform magnetisation leads to acceptable results for technical design. The simulation of the

dynamic behaviour of the whole system is possible at present time. To authors’ knowledge no similar method was found in literature.

ACKNOWLEDGEMENT Thanks to the fund of the Ministry of Industry FT-TA3/017.

Literature 1. KOŠEK, M., MIKOLANDA, T., RICHTER, A.: In: Proceedings of Technical Computing. 2007, Prague, Czech Republic, 78. ISBN 978-80-7080-658-6.

EVALUATION AND FUTURE THE ULIMATE LIMIT STATE DESIGN IN GEOMECHANICS

P. Koudelka

Abstract The introduction of seven out of eight EUROCODES (1-6, 8) was not so difficult like EUROCODE 7 (Geotechnical design) which has met theoretical problems. The problems do exist in the application of the limit states theory to the field of geotechnical design. The problems appeared clearly at IWS Dublin 2005 on Evaluation and Implementation of EC7-1 (final draft EN 1997-1) “Geootechnical design: Part 1 – General rules” (great discussion forum for a general international evaluation of the final draft). This theory was formulated for geomechanics after 1950 (most probably it is possible to refer to Brinch Hansen, 1953) with, however, one fundamental fatal error, i.e. the introduction of substitute material physical characteristics to computation models which is at variance with the fundamental principles of mechanics. Almost all problems of geotechnics are significantly and complexly non-linear and the behaviour of theoretical models with different characteristics is different. This conclusion was attained in the Czech Republic after several decades of limit states design application to geotechnics and after far-reaching theoretical studies. The paper presents an evaluation both of the “IWS Dublin 2005” results and the followed development in geomechanical designs. Some conclusions for theoretical research and practice are submitted.

23

Key words geomechanical design, Ultimate Limit States, partial material factor, probability-based design, advanced numerical models

I

n mechanics (except for the geotechnical Limit States Designs) it is generally respected that in the cases of non-linear behaviour of the structure (2nd order theory, elasticplastic state) the principle of superposition is not applicable and the computation of individual effects cannot be based on coefficients or additions of individual effects. In such cases every possible dangerous state and each of design situations must be analysed separately.

The present basis of the LSD theory in geotechnics does not take the non-linear behaviour of soils and rocks into account. The little acceptable derivation concept of property design values (analogously with man-made structures) applies particularly to the ULS (its unacceptability for Serviceability Limit State was recognized earlier). The definition of the statistically derived characteristic value as the value with the 5 % probability of occurrence of worse value governing the occurrence of the limit state, at variance with its term („characteristic“) changes the physical characteristics of the analysed model towards a low probability of the design model. The partial factors on ground properties further change the strength characteristics of soils and rocks towards even lower probability. When applied in the process of computation these modifications of design values radically change the properties of the analysed soil mass model, i.e. the properties of a structural system with non-linear behaviour, which, in the end, is improbable and almost dissimilar to actual system. The above-described situation results in the fact, which can be called the Substitutive Properties Paradox, which can be defined as follows:

In a structural system with non-linear behaviour we analyse a not very probable (or almost improbable) state, paying no attention to the most probable behaviour of the soil (rock) structure. Thus we do not know the actual reliability (or risk) of the soil (rock) structure, because this reliability and risk do not correspond with the combination of coefficients used. This appears the problem hearth of geotechnical designs according to the Limit State Design Theory and according to EC7-1 especially being long decades. Due to it the final draft of EC7-1 was evaluated on a base of wide international collaboration. The base for the evaluation was an International Workshop on the “Evaluation of Eurocode 7” (IWS Dublin 2005).

IWS DUBLIN 2005 The workshop was held in Trinity College Dublin on 31st March and 1st April 2005. This workshop was organised by the European Regional Technical Committee 10 (ERTC 10) of the International Society for Soil Mechanics and Geotechbnical Engineering (ISSMGE), by the Department of Civil, Structural and Environmental Engineering, Trinity College Dublin and Technical Committee 23 (TC23) of ISSMGE. A total of 55 participants attended the Workshop from 18 countries, 16 of these being European countries. And the situation of the time? The EC7-1 development had reached a very important stage, it had received a positive formal vote and thus been ratified by the CEN member states in April 2004 and CEN had issued the definitive text of EC7-1 in November 2004, this date is known as the Date of Availability (DAV). Following the DAV, there was a two-years National Calibration Period, i.e. until

24

November 2006, during which each national standard organisation had to prepare its National Annex with its Nationally Determined Parameters (NDPs), i.e. partial factor values and values of other factors, so that EC7-1 can be implemented in its country.

settlement of 25 mm and maximum tilt is 1/2000. Actions: Gk = 3000 kN, Qvk = 2000 kN, Qhk = 400 kN at a height of 4 m above the ground surface. Variable loads are independent to each other. Ground properties: c´k = 0 kPa, Ф´k = 32° kPa, γ = 20 kN/m, E´k = 40 MPa. Require foundation width B. 3. Pile Foundation designed from soil parameter values: Situation: bored pile of 0.6 m diameter, groundwater at depth of 2 m below the ground surface. Actions: Gk = 1200 kN, Qk = 200 kN, concrete weight density = 24 kN/m3. Ground properties: c´k = 0 kPa, Ф´k = 35° kPa, γ = 21 kN/m3, SPT N ´25. Require pile length L. 4. Pile Foundation designed from pile load tests: Situation: driven piles, diameter = 0.4 m, Length = 15 m, allowable settlement of 10 mm, no transfer the load. Actions: Gk = 20000 kN, Qk = 5000 kN. Pile resistance: 2.static pile load tests, loaded beyond a settlement of 40 mm to give limit load. Require number of piles needed to satisfy both ULS and SLS. 5. Cantilever Gravity Retaining Wall: Situation: height of 6 m, base and wall thickness = 0.4 m, embedment depth of 0.75 m, groundwater at depth below the base, ground behind the wall slopes upwards at 20°. Actions: characteristic surcharge behind wall 15 kPa. Ground properties: sand beneath wall: c´k = 0 kPa, Ф´k = 34° kPa, γ = 19 kN/m3. Fill behind wall: c´k = 0 kPa, Ф´k = 38° kPa, γ = 20 kN/m3. Require width of wall foundation B, design shear force S and bending moment M in the wall. 6. Embedded Sheet Pile Retaining Wall: Situation: excavation depth of 3 m. Actions: characteristic surcharge behind JJ

JJ

Concept of the Workshop

JJ

Prior to the Workshop, 10 geotechnical design examples involving 5 different ranges of geotechnical design were distributed to the members of ERTC 10, Geotechnet WP2 and TC 23. These examples include 2 spread foundations, 2 pile foundations, 3 retaining walls, 2 designs against hydraulic failure and a road embankment on soft ground. A large number of solutions were received to these examples, which were prepared by geotechnical engineers from many countries. The solutions were sent to five reporters who were asked to examine the received solutions and identify the reasons for the scatter, i.e. ranges of solutions, and determine if this was the different interpretations of EC71 or due to other reasons (G. Scarpelli, V.M.E. Fruzzetti, R. Frank, B. Simpson, T. Orr and U. Bergdahl).

Given examples The workshop organizers prepared the following set of geotechnical design examples: 1. Pad Foundation with vertical load only: Situation: embedment depth of 0.8 m, groundwater at the foundation base, allowable settlement of 25 mm. Actions: Gk = 900 kN, Qk = 600 kN, concrete weight density = 24 kN/m3. Ground properties: cuk = 200 kPa, c´ = 0 kPa, Ф´k = 35° kPa, γ = 22 kN/m3, SPT N= 40, mvk = 0.015 m2/MN. Require foundation width B to satisfy both ULS and SLS. 2. Pad Foundation with an inclined and eccentric load: Situation: embedment depth of 0.8 m, groundwater at great depth, allowable JJ

JJ

JJ

JJ

JJ

25

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ JJ

wall 10 kPa, groundwater level at depth of 1.5 m below ground surface behind wall and at the excavation surface in front of wall. Ground properties: sand beneath wall: c´k = 0 kPa, Ф´k = 37° kPa, γ = 20 kN/m3. Require depth of wall embedment D, design bending moment M in the wall. 7. Anchored Sheet Pile Quay Wall: Situation: quay height of 8 m, horizontal tie bar anchor placed 1.5 m under surface. Actions: characteristic surcharge behind wall 10 kPa, groundwater levels at depth of 4.7/5.0 m below ground surface behind/in front of wall resp. Ground properties: sand beneath wall: c´k = 0 kPa, Ф´k = 35° kPa, γ = 18 kN/m3. Require depth of wall embedment D, design bending moment M in the wall. 8. Uplift of a Deep Basement: Situation: Long structure, 15 m wide, with a 5 m deep basement. Actions: characteristic structural loading gk = 40 kPa, concrete weight density γ = 24 kN/m3, wall thickness = 0.3 m. Ground properties: sand beneath wall: c´k = 0 kPa, Ф´k = 35° kPa, γ = 20 kN/m3. Require: thickness of base slab, D for safety against uplift. 9. Failure by Hydraulic Heave: Situation: Seepage around an embedded sheet piles retaining wall, excavation depth of 7 m. Ground water level 1.0 m above ground surface in front of the wall. Actions: No other. Ground properties: γ = 20 kN/m3. Require: Maximal height, H of water behind the wall above ground surface in front of the wall to ensure safety against hydraulic heave. 10. Road Embankment: Situation: A road embankment with width at the top of 13 m is to be constructed over soft clay, side slopes keep relation of 1:2. JJ

JJ

JJ

JJ

JJ

JJ

JJ JJ

Actions: Traffic load on embankment qk = 10 kPa. Ground properties: Fill for embankment: c´k = 0 kPa, Ф´k = 37° kPa, γ = 19 kN/m3. Clay: cuk = 15 kPa, γ = 17 kN/m3. Require: maximal height, H of embankment.

These individual examples, of course, could not show solutions of the tasks through all parameters scales. However, despite it, the solution large number brought very worth knowledge on an international design practice and the code applicability. Let us to have a look at the results.

THE WORKSHOP RESULTS

JJ

JJ

JJ

JJ

JJ

JJ

JJ

JJ JJ JJ

JJ

Geotechnical engineers from many countries prepared a large number of solutions to these above-presented examples. It was found that there was considerable scatter in the solutions received for the most of these design examples. T.L.L. Orr presented the ranges in the ultimate limit state solutions received for the examples in the form of how much the maximum or minimum values for the requested parameter are greater or less than the mean of the maximum and minimum values, expressed as a percentage of mean of these values. The result range can obtain also using another point of view if we compare the maximal value to the minimal ones and express the scatter in percentage of the minimum. Both approaches are involved in Tab. 1. T.L.L. Orr prepared a set of fully worked model solutions, using his preferred calculation models and design assumptions. The results of the model solutions are summarised in Tab. 2 with model solutions for ULS design, using the three Design Approaches where relevant, presented in bold. The ranges of the model solutions due to the different Design Approaches are much smaller than the ranges of the received solutions in Tab. 1. This is caused obviously due to the unified procedure, partial factors and algorithms.

26

Example

Type

Parameter

Range of Received Solutions

% Range T. Orr

to minim.

1

Spread Foudation, vert. load

B - foundation width

1.4 - 2.3m

±24%

64%

2

Spread Foudation, incl.ecc.load

B - foundation width

3.4 -5.6m

±24%

65%

3

Pile Foundation - from soil para.

L - pile length

10.0 - 4.2.8m

±62%

328%

4

Pile Foundation - from pile tests

N - number of piles

9 - 10

±5%

11%

5

Gravity Retaining Wall

B - wall base width

3.1 - 5.2m

±37%

68%

6

Embedded Retainig Wall

D - embedment depth

3.9 - 6.9m

±37%

77%

7

Anchored Retaining Wall

D - embedment depth

2.3 - 7.0m

±51%

204%

8

Uplift

T - slab thickness

0.42 - 0.85m

±33%

102%

9

Heave

H - hydraulic height

3.3 - 8.8m

±45%

167%

10

Embankment on soft ground

H - embankment height

1.6 - 3.4m

±36%

113%

Tab. 1: Ranges of received ULS solutions for the examples using EC7-1 (After T.L.L. Orr)

Tab. 2: Summary of model solutions with ranges of model solutions for ULS design (by Orr)

EVALUATION

Example 6: Embedded Retaining Wall

The solutions of contributors were evaluated by the reporters respective to the examples. A presentation of the complete workshop evaluation of EC7-1 is out of the Paper range. However, let we look at results of the examples 6 (Fig. 1) and 10 (Fig. 2) more in detail.

The given situation, inputs and require are presented in Chapt. 2, the following Fig. 1 shows the example in general. B. SImpson´s evaluation can be find in Fig. 3 further. Points on the graph are annotated as follows to represent the various EC7-1 design approaches (DA): 1 – DA 1, taking the worst case of Combination 1 and 2; 2 – DA 2; 3 – DA 3 and N – an existing National method. The horizontal axis gives a scale to re-

27

quired embedment values in meters, a country denotation of the contributors are added to the vertical axis however, it is not obvious.

We can see the National solutions (N) give the more effective results generally. The accordance of the most their results about embedment of 4m is remarkable. The lower effectiveness of the designs according to the all EC7-1 approaches is clearly obvious. The author’s calculations are placed in the lower half of Fig. 3 between two red lines. The presented black annotation of two designs according to EC7-1 is not correct: the design denoted black “b” accords with DA 2 (marked red – value of 3.5m) and similarly design denoted black “1” with DA 3 (red – value of 3.9m). Two other designs according to Czech standards denoted “N” (in red circles) respect two different theoretical accesses: the one accords to the optimal values of active earth pressure for the peak shear strength state (short-term retaining structures - value of 3.2m), the other represents design for the residual shear strength state (longer-term retaining structures - value of 4.2m).

Fig. 1: Given example 6: Embedded Retaining Wall

If we do not consider the lowest national faroff value on the first horizontal line (about 2.6m what is obviously too low) the scatter of example calculations is between values of 3.2 m and 6.9 m. The difference between the lowest considerable value and the low limit of the scatter presented by T. Orr in Tab. 1 (3.9 m) is not negligible. This fact shows that both Tab. 1 and Tab. 2 include solutions according to EC7-1 only and that generally the solutions ranges are significantly wider.

All four designs belong to the most effective ones of the whole set.

Example 10: Embankment on Soft Ground The material data of the example are given probably according to a local experience but not in accordance to theoretical and physical principles: shear strength of embankment are given in terms of effective stress however, shear strength of clay is given in term of undrained value. Thus, without any doubt, the results are influenced due to this incorrectness and have not full validity.

Fig. 2: Given example 10: Embankment on soft ground

28

Country 4 - approaches of EC7-1: DA1a-b-2a-b, DA3a-b; computing programme PostoGRAF v. 3.0 (Bishop method of slices). Country 5 - approach and Global Bearing analysis by Taylor and Swisscode; Country 6 - approaches of EC7-1: DA1-2; over all stability analysis for slopes (SLOPE W). Country 7 - approaches of EC7-1: DA2 and by National Code; analysis according to Swedish slip circle. Tab. 3 shows the wide scatter of the results. The most of them around embankment height of 2.2m are probably in accordance with the local experience of the example author. This experience includes doubtless also other material properties and local peculiarities (pore pressure, moisture, soil grains, geological development and others). If the clay undrained shear strength is substituted by effective stress values for soils of the group F7 according to CSN 73 1001 (Czech Standard) then a solution leads to the values in red circles. The difference between the both solutions (EC7-1/Safety Factor Design) is also very wide and shows the lower effectiveness of ULS design according to EC7-1. The example does not appear to be suitable for the evaluation.

CONCLUSION TO ULS DESIGN Fig. 3: Results of the Ex.6: Embedded Retaining Wall - embedment in m

Despite it let us to have a look at evaluation in Tab. 3. The results are sorted according to the design approaches used in 7 groups named like Country: Country 1 - approach DIN 1054; bearing capacity formula. Country 2 - approaches of EC7-1: DA1-2, DA2, DA3, OFS; bearing capacity formula, Annex D, analysis according to Bishop simplified method of slices. Country 3 - approach of EC7-1: DA3; bearing capacity formula, Annex D.

29

The workshop evaluation of EC7-1 is very important and has brought very important knowledge. The evaluation is not the only one. An earlier evaluation of four basic geotechnical tasks (slope stability, earth pressure, shallow and pile foundations) has been carried out at the Institute of Theoretical and Applied Mechanic of Czech Academy of Sciences. These four studies analyzed the problems not example by example but in wide usual scales of all parameters. These analyses brought the wide valid results and similar conclusions as the workshop. The general conclusion can be formulated as follows. Theoretical base of the ULS geotechnical design is not in concordance with the principles of mechanics and this fact has a principal influence

Tab. 3: Results of the Ex.10: Embankment on Soft Ground - embankment height in m

for design. Except it, the theoretical ULS design concept of EC7-1 and Limit State Design Theory (quasi-probabilistic method) after long-term development (about 50 years) does not correspond to contemporary technical and theoretical possibilities of state of the art.

FUTURE OF GEOTECHNICAL DESIGN An more long-term application of the contemporary ULS Design on quasi-probabilistic concept based appears counter-productive and problematic without some corrections of EC7-1. These can be carried out in the National annexes. The concentrated attention need especially the characteristic value definition, both material partial factors and partial factors for resistances in Annex A, concept of earth pressure and some less important other. That corrected code would be used some time until development finish of a new fully modern concept and a code.

From contemporary point of view there can be found that a good concept of geotechnical design for the future appears in fully probabilistic methods. These methods are applied more and more in other ranges of structure mechanics.

ACKNOWLEDGEMENT The Grant Agency of the Czech Republic and the Grant Agency of the Czech Academy of Sciences provided financial support of the connected research (GP Nos.103/2002/0956, 103/2005/2130, 103/07/0557, 103/08/1617 and No. A2071302 resp.). The author would like to thank them all for support.

Literature 1. ČSN 73 1001 Shallow foundations, CSNI, Prague, 1987. 2. EUROCODE 7 November 2004. Geotechnical design – Part 1: General rules (Final draft). Brussels, CEN/ TC 250/SC7-WG1. 3. ORR T.L.L. et al.: Evaluation of Eurocode 7. Proceedings of the International Workshop. 2005, Dublin, Ireland.

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CONTACTLESS ANGLE TRANSDUCER DEDICATED FOR DC MICROMOTOR

M. Bodnicki, H. J. Hawłas

Abstract Presented transducer realizes idea of detection of mechanical quantities in electric micromachines on basis of electrical signals. Changes of the resistance cause pulsation of the current passing in the armature circuit and its frequency is dependent on the number of commutator sectors. One decided to examine a possibility of using a transducer, determining the angular position of the rotor on the basis of modulations of the armature current mentioned above. The LEM (based on Hall Effect) sensors are used as current/voltage transducers. The advantage is elimination of galvanic contact between armature and measurement unit. The originality of new solution is method of the elimination of component proportional to mechanical load from the current signal. Proposed method was testing on computer simulation way and in physical experiment then the prototype was built. New transducer is proposed for control application in high dynamic DC drive systems of small size mechatronic devices.

Key words angular position, measurement, contactless transducer, mechatronics, DC micromotor

A

pplication of mechanical commutators in DC micromotors causes pulsation of the current passing in the armature circuit. Its frequency is dependent on the number of commutator sectors. Number of pulses per one revolution of the rotor is determined by the formula n = 2k, where: n – number of pulses, k – number of commutator sectors. They had various design solutions of the commutator, among other things, various brush units (graphitoidal brushes, metal brushes collaborating with cylinder segments or ring sectors).

31

Positive side of the current pulses could be using them to the identification of the angular position of the micromotors rotor. With the positive effect was made in Institute of Micromechanics and Photonics the study of the new transducer - transforming pulses of the current into the digital measuring signal. The first idea of the measuring path has been presented in papers [1-3]. In Institute of Micromechanics and Photonics [4] made complex experimental analysis of influences of kind of micromotor, conditions of work, their wear on changes of resistance. The

examples of signals, which are representative for those examinations are presented on Fig. 1 (those signals are in fact input signals for measuring unit).

JJ

There are following conclusions for this analysis: JJ JJ

JJ

High frequency noises are the effect of friction in pair: brushes and segment of commutator; For typical supply voltage (higher than 1/6 of nominal value) amplitude of the noise

JJ

a)

is constant (under the load ½ to nominal value; but its value is higher then in noload situation); Work under extremely load is dangerous for lifetime of the motor (big currents and sparking; Constant component depend on load (its also clear from mathematical model of DC micromotor) The firs harmonic is an effect of eccentric of the rotor – this harmonic could be hard to elimination.

b)

c)

Fig. 1: Input signals for measuring unit obtained during work various kinds of DC micromotors [4]: a) Ordinary micromotor (for popular electric toy); b) world famous manufacture, long work under load; c) world famous manufacture

ALGORITHM OF THE NEW TRANSDUCER As a first step the analysis of the high limit of the frequencies of the commutation phenomena was done. For the DC motors with no-load speed to 20.000 rpm (estimated) and to 13 sections in commutator the high limit of the pulsation could be circa 50 kHz. It means – the higher components in the current signal could be take as noise.

The following algorithm was than proposed: a. Filtering of the high frequency noises; b. Detecting and separation of the “medium signal” (component proportional to load of the micromotor, determined on way of filtering “step a” signal); c. Subtraction of the “medium signal” from the filtering (step a) signal – generation of the differential signal; d. Digitalization of the differential signal generation of the TTL pulses;

32

The structure of the measuring unit is presented on Fig. 2. The LEM (based on Hall Effect) sensors are used as current/voltage transduc-

ers. The advantage is elimination of galvanic contact between armature and measurement unit.

a)

b)

Fig. 2: Structure of the measuring path: a) basic version, b) advanced version with additional filtering and buffering.

Then the test on prototype was done. The optimization of the filter parameters was made a)

successfully. The exemplary results are presented on Fig. 3. b)

Fig. 3: Elements of the optimization of the filtering block:a) too small frequency limit, b) final effect of optimization

The transducer of angular position, simplified this way, was laboratory tested within the range of observing the shape of the output signal from

33

the transducer while staring the micromotor, as well as under steady-state conditions of its operation. During these studies, one selected also

the triggering level of the flip-flop digitizing the signal. The effect was positive. The system operates correctly under variable conditions of loading. In accordance with the expectations, the trend within the input signal, resulted by

an instantaneous value of the torque braking the motor, is being eliminated correctly. The system is more effective the old version with measuring resistance [1].

a)

b)

Fig. 4: Signal generated by LEM transducer and finally output signal of the encoder: a) dynamic situation (start-up of the DC motor), b) work with stabile angular speed of the DC motor

SUMMARY AND CONCLUSION The laboratory test of prototype was done. Transducer works correct. There are the following advantages of the unit: JJ

JJ

JJ

JJ

Now the next version – optimized from point of view of miniaturizing – is taken in to consideration.

galvanic isolation from the motor armature good detection of the first pulse in dynamic applications the tuning in wide range and fitting to the specific micromotor is possible; constant length of the output pulses (and distance between following two is proportional to the angular speed of the motors rotor).

34

Literature 1. BODNICKI, M.: Encoder Using Pulsation of the Current in DC Micromotor - Model Tests. Hydraulika a Pneumatika, v.2, no. 2, 2000, pp. 35-36. 2. BODNICKI, M.: Additional effects of commutation phenomena in DC micromotor - identification and application for positioning. In Proceedings of the 47. Internationales Wissenschaftliches Kolloquium Technische Universität Ilmenau, 23-26.09.2002, Ilmenau (Germany), pp. 143-144 (Full text on CD). 3. BODNICKI, M., ROMANOWSKI, J.: Przetwornik położenia kątowego wirnika mikrosilnika. Pomiary. Automatyka.Robotyka. no. 7/8, 2001, pp. 46-51. 4. ROMANOWSKI, J.: Opracowanie metody i układu badawczego do identyfikacji położenia siłownika mikromodułu napędowego. MSc Thesis, IMiF PW, Warszawa, 2000. 5. WIERCIAK, J.: Model mikrosilnika prądu stałego w pomiarach jego charakterystyk obciążeniowych. Zeszyty Naukowe Politechniki Śląskiej no. 1230, pp. 401-407. Gliwice 1994.

TUBULAR METAL POWDER PERMEABLE MATERIALS WITH ANISOTROPIC STRUCTURE AND THEIR APPLICATIONS

V. Lapkovsky, V. Mironov, V. Zemchenkov, I. Boyko

Abstract The review of the theory and known methods of producing of porous powder materials (PPM) with anisotropic structure is revealed. The new devices for water and gases filtration with filtering elements from PMM with anisotropic structure and the examples or their perspective application is offered. The advantages of the PMM with anisotropic structure in comparison with PMM with isotropic structure are proved. Special attention is given to the producing of the tubular metal powder anisotropic materials by the magnetic-pulse compacting. The possibilities of changing of the porous structure and properties of detail from compacted powder material during deformation in pulse electromagnetic field are offered. The examples of producing of the permanent connections of the tubular and rod details are shown.

35

Key words metal powder goods, permeable materials, anisotropic structure, magnetic-pulse compacting

T

he intensive development of industry, agriculture, and cities require creation and introduction of new highly effective equipment for the purification of drinkable, sewage and industrial water, foodstuffs, other liquid and gaseous media from the pollution and toxic substances, the protection from noise of industrial installations and transport means. Porous powder materials (PPM) and articles have many applications in various industrial fields. A production of such materials requires the special technology of material synthesis and preparation [1], moulding, sintering and treatment [5,8]. On the basis of PPM the articles for the protection of environment (aerators and dispersers for the systems of the preparation for drinking water and purification of waste water, filters, sound suppressors and others are developed [6].

PRODUCTION OF THE ANISOTROPIC PERMEABLE MATERIALS BY THE METHOD MIOM (MAGNETIC PULSATION TREATMENT OF METALS) Magnetic-pulse extrusion PPM are characterised by a number of the structural and operational parameters, which are determined by the properties of initial powders. The method of magnetic-pulse extrusion PPM proved its expediency with the manufacture of lengthy and thin-walled porous and multilayer articles [2,7]. In this case molding article in the inductor without its displacement (Fig. 1a) and step molding (Fig. 1b) are distinguished.

Fig. 1: The diagram MIOM (magnetic pulsation treatment of metals) of powder in the shell without the displacement (a) and step molding (b) 1- inductor; 2- electrically conducting shell; 3- silencer; 4- powder

During the extrusion of powder according to the first diagram a certain change in the porosity of models occurs, which is connected with a change in the electromagnetic pressure at the ends of the pipe (Fig. 2). In this case the introduction into the cavity of the inductor of the billet as a result of the manifestation of axial skin

effect is observed a local increase in the pressure, and consequently increase in the density. This pressure increment negatively affects the quality of articles. The most effective combat means with this phenomenon is the screening of ends cast.

36

Step molding

Fig. 2: Change of electromagnetic pressure along the axis of inductor - without the component (1); with the shell, but without the powder (2); with the powder (3)

The more complex nature of the distribution of the density (porosity) of article in the radial section. The estimation of this phenomenon was accomplished by measurement of Vickers hardness (depression of diamond pyramid with the effort 50 N [4]). Measurements shown the decrease of the density (hardness) towards the centre of the sample. In this case the anisotropy of properties in the radial direction grows with an increase in the energy level of extrusion. The study of the properties of tubular models with the small wall thickness proves the possibility of achieving the uniform distribution of properties.

For preparation of the lengthy components with length-diameter ratio from 10 and more find the so-called radial- sequential methods of packing (or step-packing) is used. The actual stress state, that appear in the transition zones, depends on the geometric relationships, which determine the angle of taper, the conditions for boundary friction powder- shell and powdermount, and also from the deformation rate. In the known method of step packing the successive pressing of the elements of article with the step is provided. In this case in the places of passage the seam is formed, which appearance is explained by edge effects and strengthening of material. We proposed the method of step packing, where packing divided into two several motions with the increased step (Fig. 1b).

APPLICATIONS OF PPM Production of the porous vaporizers Studies were conducted on the powders of titanium of the stamp PTES-1 (ПТЭС-1) of fraction from 63 to 300 mkm. Specific area of the particle was 0.24 – 0.46 m3/g., and bulk density varied in the range from 710 to 860 kg/m3. Porosity, permeability according to the results of mercury porosimetry are given in Tab.1.

Size of particles, mm

General porosity, %

Coefficient of permeability, k*1013 m2

Size of pores (Max), mkm

Size of pores (Average), mkm

Average size of pores by mean of mercury porosimetry, mkm

-315 +200

32

34

40

19

19.4

-200 +160

31

10

21

12

14.4

-100 +63

44

7

14

9

9.5

Tab. 1: Properties of articles made of the powder of titanium according to the method MIOM (magnetic pulsation treatment of metals)

Sintering was conducted in the vacuum. a study of pore structure was conducted by mean of the mercury porosimeter of Mikrometriks (USA). The samples of articles show the high coefficient of permeability on all ranges of porosity. PPM from the powder of titanium were successfully tested for preparing the vaporizers of the

37

camera of vapour plating. With the production of the complex constructions the method of welding separate elements was applied.

Production of thermal pipe elements As is known [8] the widest application find thermal cylindrical pipes with the porous layer, fixed on the internal wall of pipe. In this case to similar elements are presented the high demands relative to the reliable metallic bond of the particles of the powder and pipe, openness of capillary structure and high permeability, and also uniformity of properties along the length. From many materials, suitable for preparing the body of thermal of pipe, copper and aluminium are processed by pulse the magnet. The centering steel support was established inside the pipe with a diameter of 16-20 mm and with a thickness of the wall of 0.5-1.0 mm and the powder of bronze was filled up (10% of Zn). The length of tube reached 600 mm. packing of powder it was achieved by mean of the device, described in the work [4]. Microstructural studies (Fig. 3) confirm the presence of a good contact between the particles of powder and the wall of pipe. Maximally attainable porosity 62-74%. For shaping of the surface of filtration perpendicular to the direction of pore channel were used the caprone filaments and fusible wires. We

for the first time developed also the method of obtaining the permeable articles from the variable surface of filtration, situated at angle with respect to the pore channels [3].

Fig. 3. Microstructure of the sintered element on the border shell (copper) and powder (bronze), porosity 40%; magnification 200x.

CONCLUSIONS 1. MIOM (magnetic pulsation treatment of metals) technique makes it possible to produce the anisotropic permeable materials with the small, average and high porosity. 2. MIOM obtained practical use with the production of the elements of vaporizers and thermal pipes.

Literature 1. Hoganas iron and steel powders for sintered components. Hoganas, 1998, 246 p. 2. MIRONOV, V: Pulververdichten mit Magnetimpulsen. – Planseebericht, 1976, Bd 24, s. 175190 3. MIRONOV, V., LAPKOVSKY, V.: Tubular articles with the high permeably by uses of the MIOM technology. In proceeding of 8th Int. Baltic conf. “Engineering materials and Tribology-2004”, Riga, Latvia, Sept. 2004, p. 201-205. 4. SCHATT, W. Einfuhrung in die Werkstoffwissenschaft.Leipzig.1984, 480 s. 5. БЕЛОВ С.В.:Пористые металлы в машиностроении.М.Машиностроение.1981,-247 с. 6. ЖЕРНОКЛЕВ, А.К., ПИЛИНЕВИЧ, Л.П.,САВИЧ, В.В.: Аэрация и озонирование в процессах очистки воды.Минск, , Беларусь, Тонпик,128 с. 7. МИРОНОВ, В.А.: Магнитно-импульсное прессование порошков.Рига ,Зинатне ,1980,196 с. 8. ПИЛИНЕВИЧ, Л.П., МАЗЮК, В.В.,РАК, А.Л., САВИЧ, В.В., ТУМИЛОВИЧ, М.В.: Пористые порошковые материалы с анизотропной структурой для фильтрации жидкостей и газов. . Минск, Беларусь, Тонпик, 250 с.

38

REWIEV OF DESTRUCTIVE METHODS OF TESTING OF THE CEMENT PASTE AND CONCRETE

P. Padevět

Abstract Abstract describe of the methods for destructive testing of concrete. For testing material properties are used methods: Determination of compressive strength of test specimens, Determination of flexural strength of test specimens, Determination of tensile splitting strength of test specimens, Determination of tensile strength of concrete, Determination of static modulus of elasticity in compression. Most important for well results of the properties of concrete are determination of size of specimens, determination of suitable equipment for testing and definition of precise boundary conditions. For definition of compressive strength is needed choose suitable shape of specimen (cube, cylinder or prism) and its size. Same conditions are important for determination of properties in tension, for splitting strength and for static modulus of elasticity too.

Key words strength, modulus of elasticity, properties of concrete

P

aper is focused on review of destructive methods of testing of the concrete. Basic methods useable in laboratory are described. Finally, methods used in laboratory, and methods recommended by standard are compared.

DESTRUCTIVE METHODS OF TESTING Material properties of concrete are possible observe by next destructive methods of testing. Methodical procedures adduced in standards describe which properties are possible get. Norm procedure do isn’t interest for properties which is possible get by analysis of data. Primary goal of norm procedure is provide similarity of process of testing.

39

In Czech Republic were valid Czech technical standards. In nineties years of last century start process of unification of the standards with European technical standards. The harmonization of the standards of testing of the concrete properties was finished, and new standards are marked like the ISO standards.

Determination of compressive strength Probably is most used test for getting the material properties. Standard unambiguously defined sizes of specimens, shapes of specimens, method of loading, and method of achieve of results. Sizes of specimens are described in standard

ISO 1920. In the ISO 1920 are defined sizes of specimen, their shapes, form of using and deviation of testing specimens. Next are defined for the compression test specimens with cubic or prism shape, eventually fragments of prisms. Length of cube edge is possible choose 100, 150, 200, 250 or 300 mm. Depth of specimen depend at the diameter of specimen. Standard recommend depth like a double size of base of prism. Second variation of specimen diameter is between 100, 150, 200, 250 or 300 mm. Third variation is use prism specimen. In this case is possible choose prism with edge 100, 150, 200, 250 or 300 mm. Length of prism is defined like a quadruple, eventually 5ty multiple of edge size. Standard recommended suitable sizes of specimens, for cube are suitable size of edge 150 mm, for cylinder 150 mm edge and 300 mm depth. For prisms is recommended length of edge 150 mm and depth 600 mm or longer. Standard of test in compression describe flatness and kind of finish of the specimen. Are possible finish compression plates of specimen with cement mortar. Range of testing equipment is defined. Strength of specimen must be minimally 10 % of range of equipment. Loading plates must by same size or bigger than specimen. One of both plates must be connected with equipment by hinge. Standard define rate of testing, it must be from 0.2 to 1 MPa/s. Loading must be fluent. Evaluation is made by achieved maximal load and loading area.

Determination of flexural strength Standard ISO 4013 depend on standard ISO 1920 (type of specimens), too. Is set using specimen with prism shapes. Testing equipment must be set with two round supports. Load is applicable by one or two loading rollers. Diameter of the rollers must be between 20 and 40 mm, and must be about 10 mm longer than width of specimen. Distance between supports must be minimally triple of width of specimen. One of roller supports can by steady, but second must be swivelling for adaptation by shape of specimen.

Standard define rate of loading, which is same range like a rate for compression testing. Lower rate is recommended for normal concrete, higher rate for stronger concrete. Evaluation and definition of strength is defined by achieved load, distance of supports, width and height of specimens.

Determination of static Modulus of Elasticity in compression Modulus of Elasticity is determined like a secant modulus of elasticity. It is quotient of difference of strength and difference of strain. Value of modulus of elasticity is presented in MPa. Basic stress is reason about 0.5 MPa and upper stress is reason at 1/3 of strength of specimen. Testing equipment have to by wit same properties like a for compression test. Gages for measuring deformation must be longer than 2/3 of diameter of specimen and placed on both sides of specimen. Maximum size of aggregates must by from 2 to 4 times smaller than diameter of specimen. Methodology of test is consequent: 3 times load from basic strength to upper strength and after then loading from basic strength to failure. Load rate must by same at start of testing like a finish.

Determination of tensile splitting strength For this test, dimensions of specimen and type of testing equipment must corresponding with SO 1920 and ISO 4012. For testing is possible use cylindrical, cubic or prism shapes of specimens. Loading is realized by spread strip with width 15 mm and height 4 mm. Rate of loading correspond with test in compression. Result (strength) is depending on maximal load, lateral sizes of specimen, length of contact lines and π.

ACKNOWLEDGEMENT This paper has been supported by Czech Ministry of Education, Youth and Sports, under project No. MSM 6840770031.

40

Literature 1. 2. 3. 4. 5.

Determination of compressive strength of test specimens ISO 4012. Determination of flexural strength of test specimens ISO 4013. Determination of static modulus of elasticity in compression ISO 6784. Determination of tensile splitting strength of test specimens ISO 4108. Determination of tensile strength of concrete ČSN 73 1318.

PROPERTIES AND QUALITY OF THE SURFACE OF IRON-COPPER POWDER DETAILS

V. Mironov, I. Boyko, V. Lapkovsky

Abstract The nondestructive methods for the quality and properties control of iron-copper powder details are analyzed. For the small details the induction method is used. The amplitude, phase and frequency spectrum of excited current depends on the shape of detail, properties and continuousness of material. The measuring transducer obtains information about the properties of detail by means of specified magnetic flow density. Experiments with details after compacting, sintering and infiltration by metallic melts based on copper are carried out. For the control of the details of complicated shape – for example, impeller of radial flow pump – the sclerometric method is used. This method allows to uncover the inequality of infiltration and to evaluate the reliability of detail parts joining.

Key words powder details, quality, measurement, control

41

P

owder metallurgy is one of the progressive methods of the manufacturing of machine details is the powder. In recent years the significant increasing of geometry, weight and complication of details shape is revealed. The details form powder alloys on the base of Fe-CCu hold a stabile substantial position as before [1]. For example, one of the new applications is the manufacturing of the details of the rotary pump for transmission of liquid petroleum derivatives [2]. Combination of high density, corrosion resistance and mechanical strength of the powder Fe-C-Cu materials and high productivity of powder metallurgy manufacturing methods (especially for complicated shape powder details) allows to this technology to gain the new applications. At the same time in technology mastering there are some problems concerned with assurance of detail uniform characteristics and quality maintenance. For example, crack formation, the necessity of mechanical operations to remove of material leavings after sintering, insufficient strength etc [3]. In this work the nondestructive methods for the quality and properties control of Fe-C-Cu powder details are analyzed and the influence of green strength, infiltration temperature and composition on the quality of details is revealed as well.

INDUCTION METHOD There are many nondestructive methods for control of the quality of details [5]. In our opin-

ion for the small details the induction method (especially for series manufacture) probably is the most effective and simple method. It is known that the amplitude, phase, trajectory, frequency spectrum and other characteristics of currents, excited in detail, depends on the shape of detail, properties and continuousness of material, distance from the transducer, frequency and speed of the detail movement. For the quality control the detail must be placed into the action field of transducer (Fig. 1). The whirling currents are excited by the variable magnetic flow Ф0 (Fig. 2). In its turn the whirling currents generate the variable magnetic flow ФB with density δ. The measuring transducer obtains information about the properties of detail by means of specified magnetic flow ФB density. Electric-field vectors of exciting field Н0 and transducer field НB are directed toward to each other. Electromotive force in the spoil of transducer is proportional to the difference of fields Ф0 – ФВ. Experimental evaluation of the applicability of this method was realized by measurement on the sintered and parts with different porosity (Tab. 1). Part with minimal porosity was as an etalon. After measurement parts was classified according to the meterage. The results of classification are fully coinciding with porosity index that confirm the applicability of induction method. Analogically were made experiments with parts after sintering and infiltration, which confirm the applicability of this method too.

Fig. 1: Measurement scheme using induction method: 1 – indicator; 2 – transducer; 3 – part

42

a)

b)

Fig. 2: Lines of fields H0, HB and density of whirling currents δ applying overlay transducer (a) and in-line transducer (b). Group of samples

Porosity, %

Group of samples

Porosity, %

1

13.2

4

21.7

2

13.8

5

24.1

3

16.0

6

28.0

Tab. 1: Groups of samples (Fe-C powder before sintering) with different porosity

The main advantages of induction method are: 1. 2. 3. 4. 5. 6.

usability; it is possible to control the motive parts; inappreciable labor input; quick-response comparison tests; easily automated method; the mechanical or electrical contact of transducer and part is not necessary.

SCLEROMETRIC METHOD In manufacturing of details from powders the infiltration method is widely used [2]. The infiltration method of the iron-copper powder details by the metallic melts on the base of iron-copper solders provides the details of high corrosion resistance, density and strength. However the investigation of infiltration process is revealed that the details refuse appear on the different stages of technological process: at pressing (no uniform density), at sintering (atmosphere influence) and during infiltration (insufficient or no uniform density). We suppose that the sclerometric method [4] is especially effective for adjasment of the technological process (Fig. 3).

43

Applying of this method and received information during investigation can help to avoid any refuse. Scratch-hardness test was made on different surfaces of the Fe-C-Cu details after sintering and infiltration. Sclerometric (scratch) hardness was evaluated by springing of the ball when ball is throwed by contracted spring. Areas of sclerometric hardness evaluation are shown in the Fig. 4. Results of the measurement are revealed in the Tab. 2. As you can see the maximal hardness in this case is in the inner face of the body (C area), but in comparison with bush hardness – the hardness of end face of the bush (A area) is greater than the hardness on the outside surface of the body (D area). We can assume, that the details from Fe-CCu powder (SC100.26+4%Cu+0.5%C) have following overall hardness: JJ JJ

JJ

after pressing – HV45…50; after sintering without infiltration – HV 100…110; after sintering with infiltration by copper – HV 160…170.

Fig. 3: Scratch-hardness testing

It could be explained by the fact that after pressing the part have high residual porosity and small strength, after sintering – strength and hardness significantly increases, but residual porosity still negatively influence. After sintering with infiltration part have zero porosity and highest hardness. The main advantages of sclerometric method are inappreciable labor input, quick performing of test, possibility to give measured values in standard hardness units HV. As disadvantages can be mentioned the mass sensitivity, method is sensitive to the workholding method of detail, residual small impression. Nr.

Fig. 4: Areas of sclerometric hardness K evaluation (Shore hardness): A – end face of the bush; B – end face of the wheel; C – inner face of the body; D – cylindrical outside surface of the body

CONCLUSION It was revealed, that for the quality control of the small details the induction method (especially for series manufacture) is one of the most effective and simple method. For the control of the details of complicated shape – for example, impeller of radial flow pump – the sclerometric method is recommended to use. This method allows to uncover the inequality of infiltration and to evaluate the reliability of detail parts joining.

A area

C area

D area

K

HV

K

HV

K

HV

1

423

196

474

209

404

154

2

425

170

475

210

359

106

3

414

160

476

210

304

85

4

421

162

475

210

304

85

5

431

185

474

209

374

124

6

433

187

473

208

401

151

7

408

157

472

201

420

167

8

413

159

475

210

439

183

9

433

187

474

209

483

217

10

424

166

470

205

399

150

11

417

160

473

208

375

126

Arithm. mean

422

168

474

209

387

139

Tab. 2: Sclerometric hardness (Shore hardness) values in the different areas and correlation with the Vickers hardness HV20 (fragment)

44

Literature 1. MIRONOV, V.: In: Proceedings of the International Conference on Powder Metallurgy. 1994, Paris, France, 2157-2160. 2. MIRONOV, V.: Materials Science, 12/2, 2006, 106-109. 3. MIRONOV, V. et al.: In.: Proceedings of the International Conference on EuroPM-2007. 2007, Toulouse, France, 439-444. 4. RUNKIEWICZ, L.: Effect of Factors on Results of Sclerometric Tests of Concrete, Building Research Institute, Warsaw 1991. 5. SAMOYLOVICH, G.S.: NDT Testing of Details, Mashinostroenie, Moscow 1976. (in Russian)

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF POLY(VINYL ALCOHOL)-PLASTER COMPOSITES

H.F. El-Maghraby, O. Gedeon, A.A. Khalil

Abstract Various additives have been attempted to improve the mechanical properties of gypsum plaster. Composite formation with polymers is one of the new routes in this regard. The current study shows some of the results of poly(vinyl alcohol) (PVA) - plaster composites. Different concentrations of PVA (0.25-4.0 wt. %) were added to the β-hemihydrate plaster. Mechanical properties including compressive and bending strengths of the neat plaster and composite samples were performed and correlated with their microstructure. Results revealed that the composite with 1.0 wt. % of PVA exhibited improved compressive and bending strengths compared to those of neat plaster and composites containing other proportions of PVA. After one week of aging, compressive strength increased from 18.2 MPa for neat plaster to 28.5 MPa for 1.0 wt. % PVA composite. Whereas, bending strength increased from 8.7 to 14.5 MPa for the same compositions and aging time. The improvement of the mechanical properties was attributed to the formation of thin layers of the polymer around the set plaster grains, adhering and binding them, and consequently improving the mechanical properties of the composites. These properties were further correlated with microstructure as clarified by scanning electron microscopy (SEM) of the set composites fractured surfaces.

45

Key words gypsum plaster composites, poly(vinyl alcohol), mechanical properties, microstructure

G

ypsum plaster is one of the eldest constructing materials manufactured all over the world. In the past few decades, gypsumbased materials have become one of the most convenient materials of choice for indoor finishing in many countries. Over 80% of all interior surfaces in European housing are either made from or lined with gypsum-based products [10]. Suitable workability and volume stability in addition to the wide abundance of its un-expensive raw materials in different parts of the world have made gypsum plaster a most widely used finishing material in construction for centuries [2]. Nevertheless, new plaster composites with different kinds of reinforcements are still being developed to improve their mechanical properties via the plaster composites formation. Combining plaster with synthetic fibers (glass, polyamide) [1, 7, 14] or natural fibers (sisal, waste paper) [5, 9] resulted in appreciable toughness values. Eve [5], for example, studied the availability of polyamide fibers as reinforcement of a commercial plaster. The presence of these water-absorbent fibers precluded the hydration of the gypsum grains located to the fibers, perturbed the arrangement of the dihydrates and resulted in a weak fiber/matrix interface. Therefore, a decrease in the mechanical properties accompanied the increase of the fiber concentration.

the flexural strength of the latex modified plaster as compared with unmodified composition was observed by Çolak [3]. This was interpreted as due to the reduction in water of workability. In contrary, Çolak [4] found in another study that the introduction of latexes such as polyvinyl acetate, styrene-butadiene rubber and polymethylmethacrylate onto plaster increases the setting time and decreases the flexural and compressive strength. Therefore, the role of latex addition to enhance the mechanical strength of the plaster would be expected to depend on a number of factors, such as the magnitude and physical nature of the interactions between the components. The chemical nature of the latex may also play an important role to affect many of the plaster properties, especially at high latex content. For example, the addition of latex containing a water-repellent component to the plaster usually increases the setting time [8]. The present study aims to characterize the poly(vinyl alcohol)/β-hemihydrate plaster composites with different weight percents of the added polymer. The impact of the poly(vinyl alcohol) addition on the mechanical properties of the set hardened plaster composites was investigated and correlated with their microstructures.

Moreover, a number of trials has been attempted to form plaster composites with latexes. It was reported that the effect of latex on the properties of plaster depends primarily on the latex / hemihydrate ratio. The magnitude of the observed effects generally increases proportionally with the increase of the amount added into pure plaster [3, 8, 13]. An increase in

46

EXPERIMENTAL A commercial-grade gypsum A commercial grade β-hemihydrate plaster (purity 96 % that previously determined [12]) (BPB Formula Gmbh, Germany) and poly(vinyl alcohol) (Aldrich-product P8136, average mol. wt. 30,000-70,000) were used. The proportion of the polymer varied between 0.25 and 4.0 % by wt. of the solid plaster powder. The percent of distilled water used was previously determined as a normal consistency of neat plaster (46 %) [6]. To measure compressive strength, 2.5 cm x 2.5 cm x 2.5 cm cubes were tested using a universal testing machine (FPZ100/1, HECKERT/ THURINGER INDÜSTRIEWERKE, Germany) at a crosshead speed of 0.56 x 10 -4 m.s-1. Bending strength was measured using 17.2 cm x 2.3 cm x 2.3 cm bars tested under three-point bending strength universal testing machine (FM250, HECKERT/THURINGER INDÜSTRIEWERKE, Germany) at a crosshead speed of 0.45 x 10 -4 m.s-1 and span of 10 cm. Both compressive and bending strengths were measured after one, three, and seven days of aging. The presented mean values in tables and figures were calculated from five specimens of the same composition.

sive strength of the tested composites increased with the increase of the polymer concentration up to 1.0 wt. % (Fig. 2). At this concentration, the strength magnitude reached to the maximum value, and then started to decrease with further addition of polymer. This ascending-descending curve was found to be similar for all the different aging times. Nevertheless, the compressive strengths of the composite samples tested after 3 and 7 days are almost twice the values of the corresponding samples tested after one day (Fig. 1&2). Comparing the compressive strength values of the samples tested after 3 and 7 days indicates an extra moderate increase in the strength of the composites tested after 7 days in comparison with those samples tested after 3 days, as shown in Figure (1).

RESULTS AND DISCUSSION

Two significant hydration effects on the compressive strength of both the unmodified and modified plaster samples with aging up to 7 days could be noticed. One of them is the enhancement in the strength with aging for 1 up to 3 days; which is attributed to the increase in the extent of hydration of plaster in the polymerfree as well as plaster polymer samples with time; reaching its highest value after 7 days [11]. On the other hand, the second one is the existence of extra amount of water used for workability, which decreases the strength by aging to 3 and 7 days due to its normal evaporation leaving behind open pores. The net result of these two opposite effects is the observed increase of the compressive strength with aging time.

Tab. (1) shows the results of both compressive and bending strengths of composite samples containing different poly(vinyl alcohol) / plaster concentrations after aging for 1, 3, and 7 days at 20±2oC and about 70% relative humidity. The compressive strength results at different aging times for the entire polymer concentrations used are graphically presented in Figure (1). It is clear from Figure (1) that the strength of both unmodified and modified plaster samples increased sharply with aging from 1 to 3 and 7 days; which is a normal behavior met with all binding and cementing materials [13]. Compres-

It is suggested that the added poly(vinyl alcohol) is forming a thin film coating the set plaster grains, increasing the interlocking among them, and consequently enhancing the strength of the composite. The extent of a thin polymer film on the surface boundaries of the set plaster is linearly increasing with the increase of the polymer concentration until the grains are fully covered. Further addition of the polymer starts to form polymer accumulates which start to be coalesced in the pores that appears due to the withdrawal of water of workability and therefore, results in a drop in the compressive

Microstructure features of Au-Pd alloycoated samples were investigated by scanning electron microscopy (SEM) (Hitachi, S-4700) equipped with an energy-dispersive X-ray (EDAX) unit.

47

Polymer/plaster wt. %

Compressive Strength (MPa) One Day

3 Days

Bending Strength (MPa)

7 Days

One Day

3 Days

7 Days

0.00

8.5±0.2

17.7±0.2

18.2±0.2

2.3±0.2

6.7±0.2

8.7±0.2

0.25

10.8±0.6

18.7±0.8

22.2±0.7

---

---

---

0.5

10.9±0.5

23.2±1.0

25.0±0.3

4.5±0.1

10.8±0.2

11.3±0.2

1.0

12.9±0.4

28.4±0.4

28.5±0.1

4.9±0.1

13.1±0.2

14.5±0.2

2.0

9.2±0.6

19.6±1.2

22.8±0.7

4.1±0.1

10.4±0.2

11.9±0.4

3.0

8.6±0.6

17.5±0.4

22.0±0.6

---

---

---

4.0

7.6±0.3

16.1±0.3

19.5±0.7

---

---

---

Tab. 1: Mechanical properties of different wt. % polymer/plaster composites tested after different hydration periods

strength [12]. This deterioration effect of the polymer on the strength is increasing with the polymer addition from 1 to 4.0 wt. %, the upper limit of the observed concentration range.

and for the entire aging times. The behavior of bending strength increase in all composites with time is also evident and could be attributed to the reasons discussed above.

This behavior shows that there was an adverse effect that took place in the poly(vinyl alcohol)/β-hemihydrate plaster composites when the percent of polymer was increased over the critical percentage of 1.0 wt. %. The percent of 1.0 wt % of the polymer, was a sufficient concentration to cover and bind all plaster grains causing the formation of glued block of a composite, explaining its highest compressive strength. Increasing the polymer concentration over this critical value, it appeared that the extra polymer concentration remained at the interfaces between these previously formed glued grains, hence weakening their interfaces and consequently causing them to fail at lower loads. On the other hand, the evaporation of the free water of workability on aging up to 7 days, helped in the progressive improvement of the strength of these composites as mentioned before.

It could be concluded from Tab. 1 that 1.0 wt. % was the optimum percent of PVA that successfully reinforced the plaster. Compressive strength value of unmodified plaster (18.2 MPa) was remarkably improved after the addition of 1.0 wt. % of PVA achieving (28.5 MPa) after 7 days aging time. Additionally, bending strength was increased from 8.7 MPa to 14.5 MPa, for the same composition and aging time. Regarding the very small amount of the polymer percent added (1.0 wt. %) to plaster that verifying these results of plaster enhancement, we can see that the obtained results are promising and beneficial for construction materials and plasterboard product.

In the light of the above discussed results of compressive strength of poly(vinyl alcohol)/ β-hemihydrate plaster composites, bending strength of the unmodified and some selected modified samples was measured. Bending strength results are given in Tab. (1). It is evidently clear from Figures (3&4) that the addition of 1.0 wt. % of PVA gave the highest values of bending strengths among all compositions

Hydration of plaster gives a crystalline porous product consisting of interlocked needlelike crystallites [7]. The relative growth velocities of different faces of the set plaster crystals determine their shape. The habit of the crystals and their intergrowth texture are important factors influencing the mechanical behavior of the set plaster [15]. Figure (5) shows SEM micrograph of unmodified set plaster aged for 7 days. Figure (6) shows SEM micrographs of some selected modified set plaster samples aged for the same time. All SEM micrographs indicate the formation of well developed set plaster interlocked crystals, leaving behind a high porosity resulted from the evaporation of the excess

48

clearly in Figures (6b&c). The coalescence of these accumulates that helped in collecting a huge number of plaster needle-like crystals (Fig. 6b&c) is suggested to be the reason of trapping of extra pores and consequently decreasing the mechanical properties. Figure (6d) shows in a high magnification, the thin film formation and the starting of the polymer coalescence with the addition of 1.0 wt. % PVA. These SEM micrographs therefore, confirm both the mechanical strength data and the suggested model, regarding the coating of the set plaster grains by the polymer thin film.

Compressive strength (MPa)

water used for workability, which amounted to about 28 %. These pores are clearly appearing with the un-modified sample as shown in Figure (5). The amount of these pores decreased with the increase of the PVA content, accompanying the formation of a polymer thin film that coats the set plaster needle-like grains. As a result, it gives a structure with a lower porosity for the 1.0 wt. % composite (Fig. 6a). The further increase of the polymer content more than 1.0 wt. % resulted in a gradual formation of a small amounts of polymer accumulates, which is appearing slightly in Figure (6a) and

Aging time (day)

Fig. 2: Compressive strength of different PVA-plaster composite with polymer concentration wt. %. Each presented point is the mean value of 5 experimental values with standard deviation not more than 1.2 MPa.

Bending strength (MPa)

Fig. 1: Compressive strength of different PVA-plaster composites with aging time. Each presented point is the mean value of 5 experimental values with standard deviation not more than 1.2 MPa. The lines are guides for an eye.

Polymer concentration (Wt. %)

Aging time (day) Fig. 3: Bending strength of different PVA-plaster composites with aging time. Each presented point is the mean value of 5 experimental values with standard deviation not more than 0.4 MPa. The lines are guides for an eye.

49

Polymer concentration (Wt. %) Fig. 4: Bending strength of different PVA-plaster composites with polymer concentration wt. %. Each presented point is the mean value of 5 experimental values with standard deviation not more than 0.4 MPa.

Fig. 5: SEM micrograph of needle-like structure of unmodified plaster

CONCLUSION The addition of poly(vinyl alcohol), PVA to a commercial β-hemihydrate plaster (Purity 96 %) has been investigated. Different concentrations of PVA ranging from 0.25 to 4.0 wt. % were used to form the composites. Mechanical properties measurements of the formed composites after aging for 1, 3, and 7 days revealed an increase in both compressive and bending strengths of the formed composites with the increase of the

polymer concentration up to 1.0 wt. %, then a decrease was observed with further higher polymer concentrations. A compressive strength result of neat plaster (18.2 MPa) was remarkably improved after the addition of 1.0 wt. % PVA achieving 28.5 MPa after one week of aging. Moreover, bending strength increased from 8.7 to 14.5 MPa for the same composition and aging time. This promising increase in both compressive strength (56 %) and bending strength (40 %) was attributed to the excellent interlocking among the needle-like set plaster crystals.

ACKNOWLEDGEMENT This work was a part of the project No 2A1TP1/063, “New glass and ceramic materials and advanced concepts of their preparation and manufacturing”, realized under financial support of the Ministry of industry and trade. It was also a part of the research programme MSM 6046137302 Preparation and research of functional materials and material technologies using micro- and nanoscopic methods.

(a)

(b)

(d)

(d)

Fig. 6: SEM micrographs of PVA-modified plasters with different concentrations (a) 1 wt. %, (b) 3 wt. %, (c) 4 wt. % of PVA, and (d) the same as in (a) with higher magnification.

50

Literature 1. ALI, M.A., GRIMER, F.J.: J. Mater. Sci. 4, 1969, 389. 2. ARPE, H.J.: Ullmann’s Encyclopedia of Industrial Chemistry, Calcium Sulfate, Wiley-VCH, Verlag, Germany, vol. A4, 1984, 555. 3. ÇOLAK, A.: Cem. & Concr. Res. 31, 2001, 1539. 4. ÇOLAK, A.: Mater. Lett., 60, 2006, 1977. 5. COUTTS, R.S.P.: J. Mater. Sci. Lett, 10, 1990, 77. 6. EL-MAGHRABY, H.F., GEDEON, O. and KHALIL, A.A.: Review of Alexander Dubček University of Trenčin, Slovakia, ISSN 1337-6047, 1(3), 2007, 39. 7. EVE, S., GOMINA, M., GMOUH, A., SAMDI, A., MOUSSA, R., ORANGE, G.: J. Eur. Ceram. Soc. 22, 2002, 2269. 8. EVE, S., GOMINA, M., HAMEL, J. ORANGE, G.: J. Eur. Ceram. Soc., 26, 2006, 2541. 9. HERNANDEZ-OLIVARES, F., OTEIZA, I., DE VILLANUEVA, L.: Composite Structures, 22, 1992, 123. 10. http://www.eurogypsum.org/pages/living2.html. 11. KHALIL, A.A.: J. Appl. Chem. Biotechnol., 22, 1972, 703. 12. OHAMA, Y. Handbook of Polymer-Modified Concrete and Mortars, Properties and Process Technology, Noyes Publications, 1995, 236. 13. RUBIO-AVALOS, J.C., MANZANO-RAMRIEZ, A., LUNA-BARCENAS, J.G., PEREZ-ROBLES, J.F., ALONSO-GUZMAN, E.M., CONTRERAS-GARCIA, M.E., GONZALES-HERNANDEZ, J.: Mater. Lett., 59 (23), 2005, 230. 14. SINGH, M., GARG, M.: Cem. & Concr. Res., 23, 1993, 213. 15. SINGH, M., GARG, M.: Cem. & Concr. Res., 27, 1997, 947.

INVESTIGATIONS OF MICROSTRUCTURE OF THE FORGING DIE AFTER USING – A CASE STUDY

J. Jasiński, G. Walczak, K. Kaczmarek, J. P. Jasiński

Abstract The paper presents the results of investigations of surface layer microstructure after using. The work conditions, wear and failure mechanisms analyze has been presented. The article presents analyze of possible phase change during exploitation processes and they exert influence to material properties. There are also shown directions of the change of tool material microstructure to improvement service life of the tool.

51

Key words tool, tool steel, surface layer, wear

T

he die forging is a widely practical in steel hoot-working technology. Lots and lots elements for the motor-car industry is performed by this method. She permits to make of various elements, not seldom being characterized with the complicated shape. Working conditions of forging dies are very difficult. They are subject on the high and cyclical changing temperature, high, cyclical changing mechanical stresses, intensive friction, and corrosive influences of processed materials and atmospheres of airs. Because of described working conditions these tools are subject on many, very complex wear mechanisms. Usually appear concurrently many phenomena having the immediate influence on the destruction of the tool [1-6]. Analyzed die was used to forge of valvular steel. Valvular steel is material with difficulty deformable. From this reason working conditions are worse in comparison to working conditions of matrices to the forging of typical structural steels [5,6].

REASONS OF THE DETERIORATIONS OF TOOLS TO THE FORGING DIE As one of major factors stimulating the deterioration of forging die one should to exchange the degradation of the structure of material in the top-layer of the tool and consequential from this fact decrease of mechanical properties. A basic reason decrease near by the work surface of the tool are tempering processes occurring in material of the tool under the influence of high temperatures during an exploitation. Causes this strong decrease of mechanical properties. In the effect increases the speed of the abrasion and comes down the resistance on mechanical deformations. In certain conditions can follow

the plastic deformation of material of the tool. In result follow further changes of mechanical properties and the degradation of the structure of material [1-6]. The plastic deformation of material of the tool can be visible in most strongly mechanically and terminally laden fragments of the die. High temperatures of the work call out tempering phenomenon and the diminution of the hardness of the alloy. One ought simultaneously to remember the strong influence of the hardness with temperature of material. The yield strength of steel in the surface operating temperature can be several times lower than at room temperature. Causes this strong growth of the risk to plastic deform of a tool material [5]. A very fundamental problem causing the deterioration of tools is wear as result of the friction. One rates that a reason back away from the exploitation of 70 % tools to the plastic reshaping is the excessive wear as result of the friction. The abrasion results the very intensive friction of material between worked material and the surface of the tool. Firsthand reasons of the high, individual force of friction are major press force and the high coefficient of friction. With the additional problem which enlarges the force of friction is crumbling up itself small parts of oxides or other hard coats to cover the work surface of the tool. The occurrence of hard small parts quickens wears [1,4]. Following, very typical for the forging technology is the deterioration of tools as the result of the thermal-mechanical fatigue. The thermalmechanical fatigue is due in cycles variable heat and mechanical stresses. Heat stresses are due changes of the temperature of the surface and thermal expansion of material die. Mechanical stresses are instead result the pressure of the stamp [3, 5, 6].

52

In high temperatures in progress of the exploitation on the surface of the tool and inside cracks can form oxides. The influence of the layer of oxides on the exploitive durability of the die can be different. If the layer of oxides creates the coat on the surface of the tool and does not crumble away, then this layer can protect die before the immediate contact of the surface die with worked material. In the effect diminishes the speed wear die. If instead this layer easily crumbles away, then among surfaces rubbing are introduced hard small parts [6].

RESULTS OF RESEARCH AND DISCUSSION

MATERIAL AND THE METHODIC OF RESEARCH

In material of the top-layer of the tool one can observe three zones about the different microstructure (Fig. 1a). From the page of the core we can notice the typical microstructure of the chisel steel after the full heat-treatment (Fig. 1b). Nearer the surface one can notice the zone more strongly tempered (Fig. 1c). Directly under the surface is visible the third zone, about greatly broken microstructure (Fig. 1d).

In the article was shown findings of forging die after the exploitation. The die made with use a PN-EN: X40CrMoV5-1 hot work tool steel. In progress of the exploitation by means of die one performed elements valvular steel. These research permitted to describe changes in material of the die intercurrent as the result of the exploitation.

In the die followed the considerable degradation of the structure of material. A principal cause of changes in the structure materials was the influence of heat on the top-layer of material. In the effect of these changes strongly came down the hardness of material of the top-layer of the tool. In fig. 1 was shown changes of the structures of material called out with the thermal influence of forged material.

Fig. 1: Structural changes in the top-layer of die material

53

With findings research of the microstructure well correlate distribution of the microhardness of the top-layer of material. At the surface of material the hardness is high, what is due with the occurrence of the layer of oxides, then comes down, and slowly grows toward the core. In material of the layer of the top-die are visible also plastic deformation of the matrix material. Fig. 2a introduces the deformed plastically zone. The thickness of the zone deformed plastically reaches in most thicker places approx. 1 mm. On Fig. 2b one introduced the area about the distinct bend of slats of the martensite. Besides the plastic deformation the subject matrix is on the strong abrasion called out a friction of forged material. In the layer of the top-die appeared also the fatigue thermal-of fatigue (Fig. 3). In the effect of processes of fatigue were developed cracks with the considerable depth. Intercurrent cracks were concentrate in the material with distinct structural changes, do not remount material of the core.

In the microstructure of material are visible also continuous layers of oxides about the considerable thickness. Because of the considerable hardness and the abrasion resistance and the small coefficient the heat conductivity they determine the protection of material of the die before the immediate tribological and thermal influence of forged material.

CONCLUSIONS JJ

JJ

JJ

Appeared strong structural changes in the top-layer of the die, local where it had an immediate contact with worked material. Lowered properties of material and influence of temperature called out the plastic deformation of material of the die about 1 mm. In the die became also noticed results of the thermo-mechanical fatigue and the oxide layers.

Fig. 2: The plastic deformation of material of the layer of the top-die

Fig. 3: Cracks of fatigue

54

Fig. 4: The oxides layer

Literature 1. BEHRENS, B., SCHAEFER, F.: Prediction of wear in hot forging tools by means of finite-elementanalysis, Journal of Material Processing Technology 167, Germany 2005. 2. JASIŃSKI, J., JEZIORSKI, L., TORBUS, R., SZOTA, M., WALCZAK, G., KACZMAREK, K.: Fluidalna obróbka cieplna stali narzędziowej, Inżynieria Powierzchni, Poznań, 2007. 3. JASIŃSKI, J.: Oddziaływanie Złoża Fluidalnego Na Procesy Nasycania Dyfuzyjnego Warstwy Wierzchniej Stali. Wydawnictwo Politechniki Częstochowskiej, Częstochowa, 2003. 4. KIM, D.H., LEE, H.C., KIM, B.M., KIM, K.H.: Estimation of die service life against plastic deformation and wear during hot forging processes, Journal of Materials Processing Technology, 2004. 5. SMOLIK, J.: Rola warstw hybrydowych typu warstwa azotowana powłoka PVD w procesie zwiększania trwałości matryc kuzniczych, Wydawnistwo Instytutu Technologii Eksploatacji, 2007. 6. ŻMICHORSKI, E.: Stale narzędziowe i obróbka cieplna narzędzi, WNT. Warszawa, 1976.

55

MECHANICAL LOAD AND MICROSTRUCTURE OF DISCHARGE JET FOR COMPRESION IGNITION ENGINE

J. Jasiński, G. Walczak, K. Kaczmarek, J. P. Jasiński

Abstract The article presents deliberations about mechanical load and microstructure of a nozzle which is an element of injection system in compression-ignition engine. In the aspect of exploitation durability and reliability improvement, numerical analysis results of state of stress and deformation are presented and also metallographic research results of unexploited nozzle. Moreover, possibilities to improve steel microstructure properties by heat treatment in fluidized bed are presented as well.

Key words nozzle, FEM, state of stress, F-A/O-D

I

n compression-ignition engine, fuel injection is made directly to combustion chamber. Because of high compression ratio, compression pressure value equals approximately 2-5 MPa. To provide high quality fuel injection which allows proper fuel atomizing in combustion chamber and fuel-air mixture forming, fuel is injected using high pressure of approximately ~200 MPa. The accountable element is the nozzle tip – the injector placed in combustion chamber of diesel engine. Work conditions analysis of compression-ignition engine shows that the nozzle is periodically influenced by variable forces coming from high pressure fuel injection, compression and combustion of air and fuel-air mixture. High combustion temperature influence and high temperature corrosion in the presence of chemically negative atmosphere contribute to significant wear of this element.

The article presents numerical analysis results of state of stress and deformation estimated by FEM method. Results evaluation was performed in the aspect of surface layer and core microstructure improvement. Metallographic investigation results of new, unexploited nozzle is shown. Microstructure pictures and microhardness distribution are presented. On the basic of the performed analysis structural effects are underlined, such as: JJ JJ JJ

dispersion of carbides precipitation, shape of carbides precipitation, quality of internal and external surface of the nozzle.

The possibility of material structure modification using F-A/O-D (atmospheric diffusional treatment technology) is analyzed.

56

NUMERICAL ANALYSIS The view of a real nozzle along with cooperating needle is shown in the Fig. 1. For numerical analysis a nozzle model was made (Fig. 1c). State of stress modelling was performed in two ways: 1. assumed injection pressure for internal surfaces was 220MPa. Nozzle was fixed in its upper part, respectively to actual injector. It corresponds to the situation when fuel is injected into the engine and compression pressure is slight. 2. injector fixed support did not change, however in this case on external surface of the injector, boundary condition of pressure value 20 MPa was put. It is related to the moment when fuel-air mixture gets combusted and pressure on nozzle walls increases.

a)

Analysis of the picture shows that the greatest stresses and deformations appear in the area of injection nozzle hole and differ considerably from the rest. Lesser wall thickness compared to the rest of the element makes higher values of stresses which results in heat and thermochemical fatigue of the material. The nozzle works in higher temperature, so excessive wall thickness would deteriorate heat abstraction, while its reducing would lead to decreasing the condition of nozzle end. Analyzing differences between the two modelling options, we can conclude that in the second case, state of deformation is lesser. It is caused by the influence of high value pressure of fuel injection, much higher than combustion pressure.

c)

b)

0

10

Fig. 1: Injector components – complementary pair: a) needle; b) nozzle; c) 3D view, longitudinal section and dimension of model for numerical analysis

The differences between the state of deformations inform us that the nozzle works in changeable conditions. Those stresses may cause complex states of material fatigue. Influence of changing temperature gradient was not considered. Still we can assume that the gradient makes work conditions of the nozzle worse, increasing state of stresses in the material in the surface layer of the nozzle.

57

METALLOGRAPHIC INVESTIGATION For the research, a new unexploited nozzle was used. The surface layer microstructure of area 2 (Fig. 1c) is shown in Fig. 3a. Two types of carbides are seen. Carbides of less dispersion are probably the result of spheroidize annealing whereas carbides of more dispersion and specific shape probably come from carburize process. Presented microhardness distribution (Fig. 3b) is typical for carburizing.

Microstructure of nozzle tip hole is shown in Fig. 4. Hole surface is non-homogenous and rough. That shape of nozzle tip hole may derive from accelerated wear, however forming such a small hole of required quality is very difficult.

SUMMARY Using steel for carburising is justified because of stresses coming from high pressure fuel injection. Construction elements which were carburised are of higher surface layer hardness, endurance and properly ductile core enables to carry periodically variable mechanical loads. Periodic fuel injection of high pressure injection value causes stresses shown in Fig. 2.

nozzle hole may result in exploitation durability increase. We can take into consideration making the hole with the use of laser heat source. From picture analysis of surface layer microstructure we can suggest the change of carburising parameters leading to carbides precipitation dispersion increase. Use of more chemically active carburising atmospheres and heating environments may increase volume fraction of the carbides along with increase of their dispersion. One of the methods to improve surface layer and nozzle core structure quality is the use of F-A/O-D technology which enables heat treatment time shortening and negative grain increase restriction, keeping the same carburised layer thickness.

Analysing Fig. 4 and hole surface shape we can assume that the hole was made with the use of electro-erosion machine. Precisely formed

Fig. 2: Stress and deformation distribution: a), b) – first case; c), d) second case

58

a)

b)

Fig. 3: Results of metallographic investigation for selected area 2 (Fig. 1c): a) surface layer microstructure in area 2 (Fig. 1); magn. 500x; b) hardness distribution

a)

b)

Fig. 4: Surface layer microstructure of the nozzle hole: a) magnification 100x; b) magnification 200x; Nital etching

Literature 1. BURAKOWSKI, T.: Inżynieria Powierzchni; WNT, Warszawa 1995. 2. DOBRZAŃSKI, L. A.: Materiały Inżynierskie i Projektowanie Materiałowe; WNT, Warszawa 2006. 3. INFORMATOR TECHNICZNY BOSCH.: Układy Wtryskowe Unit Injector System/Unit Pump System 4. JASIŃSKI, J.: Oddziaływanie Złoża Fluidalnego Na Procesy Nasycania Dyfuzyjnego Stali: WIPMiFS PCz, Częstochowa 2003. 5. OSIPIUK, W.: Deformacja Niesprężysta I Pękanie Materiałów – PB, Białystok 1999. 6. RAKOWSKI, G., KACPRZYK, Z.: MES - Metoda Elementów Skończonych W Mechanice Konstrukcji - WPW, Warszawa 2005. 7. ZAGRAJEK, T., KRZESIŃSKI, G., MAREK, P.: Metoda Elementów Skończonych W Mechanice Konstrukcji – ANSYS – WPW, Warszawa 2005. 8. ŻMICHORSKI, E.: Stale Narzędziowe i Obróbka Cieplna Stali Narzędzi; WNT, Warszawa, 1976.

59

NEURAL NETWORKS MODELING CARBONIZING PROCES IN FLUIDIZED BED

M. Szota, J. Jasinski

Abstract This paper presents neural network model used for designing the assumed curve of hardness after carbonizing car drive cross in fluidized bed. This process is very complicated and difficult as multiparameters changes are non linear and car drive cross structure is non homogeneous [1÷2]. This fact and lack of mathematical algorithms describing this process makes modeling required curve of hardness by traditional numerical methods difficult or even impossible. In this case it is possible try using artificial neural network [3÷7]. Special prepared neural network model, after putting expected values of assumed hardness curve in output layer, can give answers to a lot of questions about running carbonizing process in fluidized bed. The neural network model can be used to build control system capable of on-line controlling running process and supporting engineering decision in real time. Neural networks model could be a help for engineering decisions and may be used in designing carbonizing process in fluidized bed as well as in controlling changes of this process.

Key words surface layer engineering, neuron networks, process modeling, artificial intelligent

T

he carbonizing process in fluidized bed is multi-parameters and complicated [1], because changes of parameters during this process have non linear characteristic. The next problem is the lack of mathematical algorithms that could describe it. Using neural networks for modeling carbonizing in fluidized bed is caused by several nets’ features: non linear character, ability to generalize the results of calculations for data out of training set and no need for mathematical algorithms describing influence changes input parameters on hardness [1,2].

The research is divided into three stages: JJ

JJ

JJ

using special computer system to obtain training data set, designing and building neural network structure, minimizing model structure, training and testing error.

At present different carbonizing techniques are used in the thermo chemical treatment. One of this is carbonizing in fluidized bed. This is characterized by high coefficient heat and mass transfer. These techniques are very often used in researching institutes and small industrial plant [8÷11].

60

WORK METHODOLOGY During the first stage of research data are obtained and formatted for training and testing. This research is moved in Biomaterials and Surface Layer Research Institute. This institute administers special computer system, which is using for visualization and control thermo and thermo chemical treatment in fluidized bed [10÷11]. This system enables high precision in dosage gas medium. Gas distribution station is used for controlling flows fife different gases. This station is controlled by special computer system. This system is built of one PC computer using Windows NT operation system and InTouch 7.1 software, which main interfaces are shown in figures 1 and 2. It is connected with GE Fanuc drivers system, which are connected with gas distribution station and used for gas dosage.

problem during car drive cross structure designed is non homogenous metallographic structure in car drive cross provide to Visteon, what is presented in Fig. 3÷5. Non homogenous metallographic structure in car drive cross causes difficulty designed carbonizing process, because is very hart obtain the same assumed hardness and thickness carbonizing layer in all material’s parts. The comparison of materials properties in one place of car cross drive (Fig. 4) to another places from Fig. 4 is presented in pictures 6 and 7.

Material for this research is provided by Visteon Industrial plant, witch produced car drive cross used in a lot car models.The main

Modeling the process using neural networks can be started from designing the structure of the network. The characteristic features of neural nets are: the number of layers, the number of neurons in each layer and kinds of neural connections. The number of neurons in input layer and the number of input parameters are usually equal. For carbonizing steel process in fluidized bed n = 13. Particular neural networks inputs are ascribed particular variables data input.

Fig. 1: Main interface of gases distribution [11]

Fig. 2: Parameters of one with fluidized beds [11]

Fig. 3: 3.1-3.4 micro-structure cross-section of car drive cross etched Nital in scale 1:50 in places shown in Fig. 6

61

The size of output layer is equal with number of searched parameters. In this case number of neurons in output layer equals eight. After fixing the input and the output layer structure the next step is designing the inside layers of the model. As mathematic algorithms describing correlations between vectors xn and yk are not known it is necessary to use an unconventional way of building the neural nets.

It is based on information about output and input. Neural connections are determined on the grounds of the identification of process rules and weights. Theoretically the problem of choosing neural structure is restricted to approximation of multivariable function for given vector xn [3]. The case discussed in this paper concerns multi-dimensional input vector and continuous activation

Fig. 4: Cross-section of car drive in which are shown characteristic places, scale 1:2

Fig. 5: 5.1-5.4 micro-structure cross-section of car drive cross etched Nital in scale 1:500 in places shown in Fig. 4

function. Building that kind of neural network model is defined by Kołmogorow statement [12]. He proved that in order to obtain k-dimensional output vector yk for n-dimensional input vector xn and continuous activation function, using one hidden layer neural network built of 2n+1 neurons is sufficient. Kołmogorow didn’t define activation function algorithm, because it is chosen for a particular process likewise the number of neurons in hidden layers which changes in range from n to 3n. In order to use the designed neural network in practice it should be taught by learning data set. The size of learning data set depends on the expected generalization degree, which is the

correct answer of model for the input data different from the data of learning set. Neural networks taught by learning set one far bigger than the number of adapted parameters of network (the quantity of synaptic weights connecting artificial neurons) would have better generalized qualities. If those proportions are disturbed, the network will have only reproduction abilities. In order to obtain the best approximation qualities for a designed model it is necessary to minimize the number of adapted parameters of network and, in consequence, minimize EG(w) - generalization error. When the generalization error increases, the model becomes interpolator for which all input signals, different from those of the training set are rejected as a measure background. In or-

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HV0,05

Plastic forming hardening zone

Distance from surface, μm Fig. 6: Distribution of microhardness in paces shown in fig. 4, before carbonizing in fluidized bed

HV10 and HV30

Material in deliver state a) HV10 b) HV30

Places (Fig. 4)

Fig. 7: Comparison of surface hardness HV30 in one paces shown in Fig. 6, to another before carbonizing in fluidized bed

der to avoid that it is necessary to minimize the generalization error by means of either building bigger training set or limiting the network structure. However limiting the network structure excessive will cause the increase of learning error EL(w), whose range from maximum EG(w) to minimum EG(w) behaves similarly to EG(w). Before it reaches minimum EG(w) starts behaving in the other way (it increases in contrast to decreasing EL(w)). This quality can be used in searching minimum EG(w), because it could in able faster selection of network structure. Direct observation of EG(w) is very time-consuming, because searching its minimum needs checking error EG(w) for fully learned network each time. A better solution is observing error EL(w), whose changes can be observed continuously during

63

teaching the network; in this case the structure of networks could be corrected each time after stopping teaching process with the constant control value of learning set, because too big a learning set causes the re-increase the generalization error.

CONCLUSION Such prepared neural network model, after putting expected values of assumed hardness curve in output layer, can provide give answers to a lot of questions about running carbonizing process in fluidized bed. The information obtained in this way can be used in practice by engineering designed running carbonizing process and property of final products. This research

will be continued to complex solve this subject and applied it in Industrial plant. The final solve this problem will be special computer system, which will be connected in real time with heat medium and gas distribution station [13]. This connect and special work application to make

possible adding new date in training and testing data. Connect this system whit heat treatment control system makes to possible on-line control running process and support engineering decision in real time [14÷15].

Literature 1. JASINSKI, J., The influence fluidized bed for diffusion saturation of surface layer of steel, Wydawnictwo WIPMiFS, Czestochowa 2003. 2. JASINSKI, J., JEZIORSKI, L., KUBARA, M., Carbonitriding of steel In fluidized beds, Heat Traetment of Metals, Vol. 12, nr 2, 1988. 3. OSOWSKI, S., Neural Network for transformation informations, Oficyna Wydaw. Politechniki Warszawskiej, Warszawa 2003. 4. RUTKOWSKI, L., Sieci neuronowe i neurokomputery, Wyda-wnictwo Politechniki Czestochowskiej, Czestochowa, 1996. 5. TRZASKA, J., DOBRZANSKI, L.A., Application of neural networks for designing the chemical composition of steel with the assumed hardness after cooling from the austenitising temperature, Journal of Materials Processing Technology 164-165, 2005. 6. SITEK, W., DOBRZANSKI, L.A., Application of genetic method in materials’ design, Journal of Materials Processing Technology 164-165, 2005. 7. DOBRZANSKI, L.A., KOWALSKI, M., J. Madejski, Methodology of the mechanical properties prediction for the metallurgical products from the engineering steels Rusing the Artificial Intelliegence methods, Journal of Materials Processing Technology 164-165, 2005. 8. Z. Rogalski, Fluidize heat treatmen, part 1, Surface Engineering no 2, Warszawa 2000. 9. BABUL, T., NAKONIECZNY, A., OBUCHOWICZ, Z., ORZECHOWSKI, D., JASINSKI, J., JEZIORSKI, L., FRACZEK, T., TORBUS, R., Industrial application visualization and computer control system of chamber for thermo and thermo-chemical treatment, Materials Engineering, no 5, 2002. 10. JASINSKI, J., JEZIORSKI, L., FRACZEK, T., TORBUS, R., CHRZĄSTEK, P., BABUL, T., NAKONIECZNY, A., OBUCHOWICZ, Z., Laboratory version of computer system for control and visualization F-A/O-D processes, Materials Engineering, no 5, 2002. 11. JASINSKI, J., Laboratory version of system for visualization and control of thermo-chemical processes, Biuletyn Automatyki ASTOR, Automatyka, Sterowanie i Organizacja Produkcji, Krakow 2004. 12. HAYKIN, S., Neural networks, a comprehensive foundation, Macmillan College Publishing Company, New York, 1994. 13. JOON-SIK SON, DUK-MAN LEE, ILL-SOO KIM, SEUNG-GAP CHOI, A study on on-line learning neural networks for prediction for rolling force in hot-rolling mill, Journal of Materials Processing Technology 164-165, 2005. 14. SVIETLICZNYJ, D., PIETZRYK, M., On-line Model of Thermal Roll Profile during Hot Rolling, Metall. Foundry Eng., 1, 27 2001. 15. KUSIAK, J., PIETRZYK, M., SVIETLICZNYJ, D., Application of artificial neural network in on-line control pf hot flat folling processes, Int. Journal Engineering Simulation, 1, 3 , 2000.

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THE STUDY OF MICROSTRUCTURE OF PRECIPITATIONSTRENGTHENING HSLA STEEL WITH COPPER ADDITION

P. Wieczorek, J. Lis, A. K. Lis

Abstract Effect of ageing parameters on the microstructure evolution and the precipitation-strengthening yield strength increase of 3NiCuCrMo10-10-2-4 steel with 1.4% Cu addition was investigated. The microstructure of the steel after water quenching and ageing at temperature 913K during 0.6 to 100 hours was observed with optical, transmission and scanning electron microscopy. EDS combined with STEM and SEM technique was used to analyze chemical composition of the precipitates. The aim of the study was to describe the role of copper in precipitation process, and to make use of copper to precipitation hardening. The quantitative determination of the average diameter of precipitates and interparticle spacing was studied to calculate the precipitation effect on yield strength according to modified equation of Orowan- Ashby’s type. Time - temperature parameters for the optimum mechanical properties of the investigated ultra low carbon bainitic steel were established. That steel belongs to a group of advanced structural steels, which are going to be applied for constructions working at low temperatures. That grade of steel is used for special applications in U. S. Navy.

Key words precipitation hardening, HSLA steel, epsilon_cu

I

n recent years, an importance of recycling steel scrap becomes higher and higher in terms of an environmental problem [1]. In particular, copper which comes from electric parts is one of harmful elements, because it is hard to be eliminated from steels and causes the hot-shortness during production of steel slabs. On the other hand, Cu addition to steels has some advantages: an improvement of oxidation resistance and large strengthening of steels. From a viewpoint of engineering applications of Cu bearing steels, it is important to understand a relationship be-

65

tween the precipitation behaviour of Cu and phase transformations in Cu bearing steels. The HSLA steel containing various alloying additions such as Cr, Mn, Mo, V, Cu and Ni apart from niobium and carbon [2]. Precipitation of carbides and epsilon_Cu phase in these steel is complex in nature due to several elements with affinity for carbon. This phenomenon plays a significant role in the microstructure evolution of this steel during thermomechanical processing [3]. Ultra low carbon bainitic steels recently have been used for pressure vessels and heavy plate hull

C

Mn

Si

Ni

Cr

Mo

Cu

Nb

Al

N

P

S

0.03

1.0

0.23

3.56

0.61

0.59

1.41

0.034

0.024

0.010

0.010

0.005

Tab. 1: Chemical compositions in weight % of the investigated steel

section of ships and for structures working at low temperature severe applications. HSLA 100 steel is a typical example of the ULCB steel family with YS=690 MPa and guaranteed Charpy V notch impact transmission temperature ITT = 189 K at the minimum impact energy of 80 Joules after quenching and tempering.

MATERIAL AND EXPERIMENTS The chemical composition of the investigated 3NiCuCrMo10-10-2-4 steel is given in Tab. 1. The 16mm plates were water quenched from temperature 1173 K. The ageing process of plates at temperature 913 K during 0.6 to 100 hours have been performed.

RESULTS The general aspects of the microstructure morphology were studied with SEM and the fine details with TEM. The SEM investigations for the quenched steel revealed that steel has a bainite-martensite structure (Fig. 1). Special coloured eatching showed that martensite fraction volume was about 55% and bainite 41%. Precipitates were not detected in microstructure after quenching. Two prevailing types of precipitates M2C carbides and ε_Cu (copper rich) precipitates were observed after ageing process. The small areas of the former austenite and new martensite islands (M-A) and tempered bainite-martensite islands (B-M) as well as carbides and ε_Cu particles redistributed uniformly within annealed ferrite matrix were observed. After ageing occurrence of recrystallization and precipitation processes was confirmed. After WQ and ageing the characteristic precipitates are shown in Fig. 2 together with corresponding mapping of some elements investigated by means of STEM-EDS spectrometer.

It was found with the help of chemical compositions investigation of precipitates, that for short ageing time first of all especially molybdenum carbides and nitrocarbides, with hexagonal structure (P 6/m mm) were nucleated in the matrix. Their influence on hardening process decreases with an increase of ageing time. Starting from 3 hours ageing influence of epsilon_Cu on the yield strength was dominated. These precipitates have cFm3m structure. It was determined by diffraction pattern in TEM. The stereological parameters like diameter, mean free path between precipitates were measured. There were used to calculate the precipitate strengthening effect on yield strength according to modified equation (1) of Orowan- Ashby’s type [4]. Results are presented in Tab. 2 [5,6]. (1) where: M is the Taylor factor, G is the shear modulus of matrix, b is the Burger vector, r is the particle radius, ν- Poisson’s ratio, λ - mean free path between particles.

Fig. 1: Bainitic-martensitic structure of the investigated steel after quenching

66

CONCLUSIONS 1. Mainly two types of precipitates were identified in the steel which were containing Mo and Cu identified as M2C and ε_Cu phase apart of niobium carbides not shown in the paper.

2. The M2C carbides were identified as Morich carbides, which were formed mainly at grain boundaries phase particles was randomly distributed in the matrix.

TEM

FE

Cu

Mo

Ni

Nb

Fig. 2: STEM-EDS elements maps of steel 3NiCuCrMo10-10-2-4 after WQ + ageing 913K/100hrs

Ageing time [h]

Radius r [nm]

Mean free path λ [nm]

Δσp [MPa]

1

7.06

314.27

71.32

3

13.11

250.16

113.116

6

15.17

260.87

113.89

10

28.56

360.42

99.79

100

62.25

492.94

95.55

Tab. 2: Influence of radius and free path between precipitates on increase in yield strength [5,6]

Literature 1. KIMURA, Y., TAKAKI, S.: Phase transformation mechanism of Fe-Cu Alloys, ISIJ Int., Vol. 37, 1997 nr 3, p. 290-295. 2. GLADMAN, T.: The physical metallurgy of microalloyed steels. London: Institute of Materials; 1997. 3. LE MAY, I., MC DONALD SCHETKY, L.: Copper in iron and steel, John Willey & Sons, New York, USA, 1982K. 4. ANDERSON, J.R., GROZA.: Microstructural size effects in high-strength high-conductivity Cu-CrNb alloys, Metallurgical and Mat. Trans. A, vol. 32A, 2001, p. 1211-1224. 5. WIECZOREK, P.: Ph. D. Thesis, Technical University of Czestochowa. 6. LIS, J., WIECZOREK, P., LIS, A.K.: Aged Bainitic structural steels with high tensile and toughness properties, Inz. Mater. R 22, No 4, 2001, p. 551-553.

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HOT DUCTILITY OF LOW CARBON STEEL (S235JR)

A. K. Lis, N. Wolańska, C. Kolan

Abstract The hot ductility investigations under strain rate 0.01/s were shown in this work. The investigations were carried out on the low carbon steel S235JR. The ductility of the steel was measured by reduction of area of fraction and elongation after the extension test in the temperature range from 700oC to 1000oC. The test was carried out with strain rates 0.01/s, which is characteristic for the continuous casting process. The microstructures analysis were carried out on samples sectioned with tensile direction at fracture. The received 25% ductility minimum of investigated steel for columnar grains were found in the temperature range 800-900oC. These temperatures are connected with band straightening in the continues casting process. The minimum in the %RA-T curves can be used to characterize the ductility trough, what gives the possibility to compare the hot ductility of different continuously cast slabs, and may be used to predict the steel susceptibility to transverse cracking during continuous casting in practice. The investigations of hot ductility are strongly connected with the technology of the hot working process and chemical composition [1-3]. The ferritebainite and ferrite-pearlite microstructures after air cooling were observed.

Key words ductility, reduction of area, elongation, hot ductility curves

T

he investigations which described the steel characteristic are strongly connected with the technology of the hot working process. The fundamental researches of material with determined chemical composition and structure are carried out to assure the appropriate conditions of later technological processes. The yield point, the tensile strength, the elongation and the reduction of area values belong to the most important properties for the plastic working. The properties of the final product strongly de-

pend on the structural changes during the thermo-mechanical treatment [1]. In the industry the conventional continuous casting operation a specially the straighten the strand is always carried out at the high temperature. That temperature in many cases corresponds with the hot ductility minimum of casting steel. All precautions are taken to edge cracking occurrence. Dynamic recrystalization cannot occur during straightening process because of not enough strain value [2-8].

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The minimum in the %RA-T curves can be used to characterize the ductility trough, what gives the possibility to compare the hot ductility of different continuous cast steels slabs, and may be used to predict the steel susceptibility to transverse cracking during continuous casting in practice [7-11].

EXPERIMENTAL The tensile tests of the S235JR steel were performed using a Gleeble 3500 machine. The system of Gleeble is suitable to carry out high temperature tests. The cylindrical tensile sam-

ples of 10 mm in diameter and 120 mm length were heated to 1300oC with 20oC/s heating rate than they were soaked in this temperature for 60 seconds. Cooling to the test temperature in the range 700-1200oC was performed at a cooling rate of 10oC/s. The test was carried out with strain rates 0.01/s, which is characteristic for the continuous casting process. Finally, the test specimens were cooled in air. The microstructures analysis were carried out on samples sectioned with tensile direction at fracture. The chemical composition of S235JR steel is given in Tab. 1.

C

Mn

Si

P

S

Al

N2

0.07

0.48

0.1

0.014

0.013

0.003

0.01

Tab.1: The chemical composition of investigation steel [%]

HOT DUCTILITY CURVE The effect of deformation was investigated at strain rates 0.01/s. Samples of examined steel come from the surface of continuously cast slab (columnar grains). The experimental data were plotted as the reduction of area at fracture in function of the temperature (Fig. 1). The %RA for the investigated steel tested at temperature 700oC is about 75%. As the temperature increases there is a rapid decrease in ductility to %RA values as low as 25% for samples tested in temperature range 800-900oC. Tensile testing at temperature greater than about 950oC for samples deformed with 0.01/s strain rate caused recovery of the ductility back to the high value about 90% at 1200oC. The loss of ductility at temperatures between 800 and 900oC causes the % RA-T plots to exhibit a ductility trough.

TRUE FLOW CURVES On the base of the test described in experimental part, the true flow curves for each of samples of investigated steel were plotted as the stress in function of the strain (Fig. 2). As can be seen the value of the maximum stress is decreasing with rising temperature of experiment. From the shape of true flow curves the kind of resto-

69

ration process can be deduced. And for sample deformed at 700oC the recovery process can be seen. For samples deformed at 1000-1200oC the recrystalization process can be observed but in the 1000oC case the recrystalization process is not complete.

MICROSTRUCTURE The deformation microstructures were characterized by optical microscopy and were taken from the neck of the sample close to the failure. Structures after deformation at temperature 900oC are shown in Fig. 3. The structure in the Fig. 3 consist of pearlite - ferrite grains mainly on the deformed prior austenite grains boundaries. In the space between the ferrite-pearlite structure the bainite grains can be seen as well as the Widmanstätten ferrite. At the sample deformed at 1200oC the structure consists of Widmanstätten ferrite and acicular ferrite. The needles of ferrite are much longer and slimmer because they were formed inside austenite grains which have grown after dynamic recrystallization. High hot ductility at temperature above 1000oC is due to dynamic recrystallization process and grain growth after deformation.

100

80

REDUCTION OF AREA, %

60

40

20

0 600

700

800

900

1000

1100

1200

1300

TEMPERATURE, 0C

STRESS [MPa]

Fig. 1: The hot ductility curve

STRAIN Fig. 2: True flow curves for columnar grained samples deformed with 0.01/s strain rate

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Fig. 3: Microstructure of S235JR steel after deformation at temperature 900 oC

DISCUSSION The microstructure in the sample neck depends on the test temperature and the strain rate of deformation. During deformation at temperatures >1000oC the ductility is very high, in accordance with the observation that dynamic recrystalization of the austenite has occurred. Dynamic recrystalization can be deduced from the flow curves (Fig. 2), in which the onset of dynamic recrystallization can be detected at the peak in stress. The ductility grows with temperature in this range and the microstructure after cooling is made of very long needle-shaped ferrite grains. That is because of austenite grain growth after dynamic recrystallization of austenite. When the dynamic recrystallization appears, the ductility of steel rises up, because each time the critical strain is reached, the grain boundaries on which cracking is taking place, are eliminated and new boundaries of different orientations are formed, so the stress concentration at the crack tip is eliminated. In the minimum the ductility is poor. The fracture mode is intergranular, with the cracks propagating along the austenite grain boundaries. In the hot ductility minimum the microstructure is changed to the Widmanstätten ferrite on the prior austenite grain boundaries and bainite with acicular ferrite inside (Fig. 3). At lower temperature only dynamic recovery is taking place (700oC and 800oC) and there is ferrite phase present in the structure during deformation at 700oC. The ductility rises up with volume fraction of ferrite.

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From all flow curves it could be concluded that the strain and stress decreased as the temperature is raised and properties like ultimate tensile strength and yield strength decreased with temperature. Fracture in hot working steels, as a result of the tensile stress, are caused by the nucleation of intergranular cracks by grain boundaries sliding and their coalescence. At low stresses cracks initiate at grain boundary ledges but at high stresses or strain rates they occur at triple junction. For ferrite the ductility increases with the temperature because of the dependence of recovery what interfered with the crack nucleation process [2-6].

CONCLUSIONS It was found that the hot ductility minimum of low carbon steel for strain rates 0.01/s is dependent on primary austenite morphology. It was established that hot ductility through is in the temperature range 800-900oC for samples from the surface. At temperature range of coexistence of two phases ferrite and austenite hot ductility is improved. The carried out investigations can be used to proper designing of plastic working processes in the range of deformation temperature selection.

Literature 1. DOBRZAŃSKI, L.A.: The engineering materials and materials design, WNT, Warszawa, 2006. 2. COWLEY, A., ABUSHOSHA, R., MINTZ, B.: Influence of Ar3 and Ae3 temperatures on hot ductility of steel, Materials Science and Technology, 14 November (1998) 1145-1153. 3. MINTZ, B.: Importance of Ar3 temperature in cintroling ductility and width of hot ductility trough in steels and its relationship to transverse cracking, Materials Science and Technology 12 February (1996) 132-138. 4. MINTZ, B., COWLEY, A., ABUSHOSHA, R.: Importance of columnar grains in dictating hot ductility of steels, materials Science and Technology, 16 (2000) 1-5. 5. MINTZ, B.: The influence of composition on the hot ductility of steels and to the problem of transverse cracking, ISIJ International, 39 (1999) 833-855. 6. CHIMANI, C.M., MORWALD, K.: Micromechanical investigation of the hot ductility behavior of steel, ISIJ International, 39 (1999) 1194-1197. 7. NOWOSIELSKI, R., SAKIEWICZ, P., GRAMATYKA, P.: The effect of ductility minimum temperature in CuNi25 alloy, AMME 2005, Gliwice-Wisła, Poland, 487-492. 8. NOWOSIELSKI, R., SAKIEWICZ, P., MAZURKIEWICZ, J.: Ductility Minimum Temperature phenomenon in as cast CuNi25 alloy, Journal of Achievements in Materials and Manufacturing Engineering 17 (2006) 193-196. 9. OZGOWICZ, W.: The relationship between hot ductility and intergranular fracture in an cusn6p alloy at elevated temperatures, AMME 2005, Gliwice-Wisła, Poland, 503-508. 10. PYTEL, S.M.: Hot ductility of continuous cast structural steels, AMTT, Zakopane, 1995, 403-411. 11. CARSI, M., LARREA, M.T., PANALBA, F.: Characterization of medium carbon microalloyed steels with boron, AMTT, Zakopane, 1995, 95-100.

EVALUATION OF MICROSTRUCTURE OF NICKEL SUPERALLOY INCONEL 792-5A AFTER LONG TERM EXPLOITATION

Z. Jonšta, P. Jonšta, V. Vodárek, K. Mazanec

Abstract Nickel superalloys are often uses for parts of turbines, which must work at high temperatures. It is so because this material must satisfy numerous extreme requirements. The most importants are heat resistance at high temperatures, resistance to fatigue damage and resistance to aggresive effect of combustion products. Long term service life and reliability of superalloys must be also satisfied. All

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of these factors are pertinent to stability of microstructure at long term exploitation. The submitted paper is focused on structural analysis of cast superalloy INCONEL 792-5A after long time annealing at high temperatures. Several strengthening mechanisms take effect in this alloy, the main mechanism is precipitation strengthening by coherent precipitates of intermetallic phase Ni3Al or Ni3(Al, Ti). Superalloy was commercialy produced (1120°C/2h/air + 845°C/24h/air) and long time annealing was carried out by regimes 900°C/1000h or 2000h, 5000h, 10 000 h. The analysis of microstructure was investigated by using the electron microanalyser JCXA 733 with energy dispersive analyser EDAX.

Key words nickel superalloy, microstructure, long term exploitation, γ’ phase

T

he paper deals with structural-material analysis of cast nickel super-alloy of the type INCONEL 792-5A after long-term annealing at the temperature of 900°C. This represents from the viewpoint of exploitation of this super-alloy the top level of its efficient use. Importance of the solution consists in the fact that higher level of alloying of investigated type of the cast Ni-superalloy shows higher level of segregation activity. This can lead at exploitation to development of specific micro-segregation processes connected with possible precipitation process, and with of either carbide or some variant of inter-metallic phases, e.g. of the type γ’ - (Ni3Ti,Al). Our paper concerns long-term exposition time comprising annealing at the above mentioned temperature

during 103 and 2.103 hours. This represents from a practical viewpoint the conditions, which from the viewpoint of technological practice can contribute to more objective assessment of service life, as well as to overall evaluation of micro-structural stability [1, 4].

EXPERIMENTAL ORIENTATION The testing material was – after conventional heat treatment to the desired quality: 1120°C/2h/air + 845°C/24h/air – annealed at the temperature of 900°C for 1000 hours and 2000 hours. Chemical composition of the superalloy is specified in the Tab. 1.

C

Mn(max)

Si(max)

Cr

Ti

Al

Fe(max)

B

0.06-0.10

0.15

0.20

12.0-16.0

3.75-4.20

3.15-3.60

0.50

0.010-0.020

Nb

Ta

Mo

W

Cu(max)

Co(max)

P(max)

S(max)

Zr

0.50

3.85-4.50

1.65-2.15

3.85-4.50

0.50

8.50-9.50

0.015

0.015

0.01-0.05

Rest of the chemical composition is Ni. Tab. 1: Chemical composition of the nickel super-alloy IN 792-5A (weight %)

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Investigation of properties of evaluated samples was made with use of the micro- analyser JCXA 733, which is equipped with energy dispersive analyser EDAX. Evaluation of micro-structural characteristics was realised in the mode of secondary electrons and knocked-on electrons (COMPO contrast). Individual co-existing phases were identified with use of quantitative EDX analysis. In this connection it must be, however, mentioned that semi-quantitative X-ray microanalysis was realised only in case of particles greater than 1μm, when the results are not significantly distorted by the X-ray signal from surrounding matrix. Micro-structure of investigated samples was formed by γ matrix, in which particles of intermedial phase γ’ were segregated. It is known from the results of existing analysis of investigated variants of heat treatment of high-alloyed Ni-super-alloys, that at usually applied twostage heat treatment an occurrence of bi-modal size distribution of particles γ’ is detected. It was observed during subsequent long-term exposition at the temperature of 900°C, that this type of distribution of particles of the γ’ phase is gradually eliminated. Chemical composition of the γ’ phase with its certain variability corresponds to inter-metallic Ni3(Ti,Al). In this respect it is also necessary to take into account the fact that this phase dissolves certain volumetric part of Ta. In connection to this well known fact, as well as to higher segregation activity of Ni-super-alloys it is necessary to take into account the fact, that there is certain difference in chemical composition of matrix in the area of dendrites and in intra-dendritic space. This fact obviously results also in change of basic range of chemical constitution of inter-metallic phase γ’.

BASIC MICRO-STRUCTURAL ANALYSIS Development of segregation processes during solidification of the given Ni-super-alloy is accompanied by formation of areas of matrix with distinctly different chemical composition, which leads logically to certain scatter in finally formed micro-structure. In the given case in

intra-dendritic areas different variant of eutectics is being formed, consisting of mixture of γ + γ’. In the areas of eutectics, which solidified as the latest, coarse particles γ’ were formed. In some cases in the neighbourhood of eutectics formations fine shrinkage porosities occurred. In intra-dendritic areas numerous carbides of the type MX precipitated, which were rich in Ta and Ti. These particles often decorated the boundaries of γ grains. It is known that carbides of the MX type are in nickel alloys unstable and that at higher temperatures they gradually disintegrate, which is accompanied by formation of particles M23C6 and phase γ’ [1]. In investigated samples the particles MX were „wrapped“ by a film of the phase γ’, the thickness of which increased with increasing duration of annealing. In proximity of some eutectic formations particles of Cr – Mo – W phase were present, or formations of the phase η, which is hexagonal phase of the type Ni3X containing mainly Ti, Ta and Al. Combination of elements in the phase Cr – Mo - W is typical for the phase M6C, however, in the work [2] the particles of similar composition were identified by electron diffraction as borides of the type M3B2, or M5B3. At the boundaries of γ - grains an occurrence of incoherent network of particles of the carbide MX and M23C6 was detected, and it was lined by a film consisting of the γ’ phase. Particles with phases rich in chromium or η - phases were observed at the grain boundaries only in very small quantity. Very positive is the fact that occurrence of such phases as η - phases, η phases, R – phases was not detected in any variants of heat treatment. Another important finding is the fact that at superimposed annealing at the temperature of 900°C no re-precipitation occurred, during which old phases are dissolved and new phases are created, and also some minority phases were not dissolved. Only the processes of growth and coarsening of particles of the phases present in the structure already after annealing time 103 hours were running. In most cases the precipitation is inter-granular, or there occurs precipitation at the phase boundary γ+γ’, which represents a certain risk of degradation process [3].

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MICRO-STRUCTURAL CHARACTERISTICS BY SELECTED VARIANTS OF ANNEALING On the basis of results of micro-structural analysis of investigated nickel super-alloy after two exposition times of isothermal annealing, namely 900°C/1000 hours and 900°C/2000 hours, it can be stated that micro-structure shows in numer-

Fig. 1: SEI; magn. 1500x



Precipitated phases were evaluated also by application of the EDX analysis, namely for the MX phase, phase rich in chromium, γ’(Ni3Ti, Al) and chemical composition of matrix. Two sets of measurements of the evaluated phase were performed. In case of observation of chemical constitution of the phase MX a big difference in data concerning Ti and Ta was found. In one case an average contents of Ta was around 75%, while in the second case it was around 48%, which represents approx. 60% of the contents established in the first case. Similar ratio was observed also in the case of Ti, which usually occurs in co-existence with Ta. In the first set of measurements the content of Ti was around 20%, while in the second set it was around 45%. It means that at higher content Ta the established content of Ti was lower. In the second set of measurements the ratio of representation of these elements in the phase MX was reverse. In case of the phase rich in chromium in the first set of measurements the content of Cr, Mo and W was found to be at the similar level, around 30%. In the second set of measurements

75

ous cases specific behaviour. This is manifested by occurrence of various morphologically different variants of minority phases. In case of the first variant of heat treatment, i.e. after 1000 hours of exposition the precipitation of γ’ - phase was detected predominantly at the boundaries of γ - grains or at the phase boundary (see Figures 1, 2).

Fig. 2: BEI; magn. 1500x

the detected content of W was lower, namely around 12 – 14%, and contrariwise the content of Cr increased to approx. 50%. What concerns chemical composition of inter-metallic phase Ni3(Ti, Al), it can be stated that there is only minimum difference in content of individual elements, although in case of Ta certain difference was found – approx. 10 %, vs. 3.5 %. On the basis of comparison of the mentioned data about chemical composition of inter-metallic phase is it possible to accept in the first approximation mutual substitutions of Al and Ta. At lower content of Al the content of Ta was higher, in the second case the mutual substitutions changed their place. Similar approach of evaluation was chosen in case of the second variant of heat treatment, i.e. 900°C/2000 hours. Here, too, two sets of measurements were made for each heat. The photos shown in the Figures 3 and 4 document the cases of precipitation of minority phases at the phase boundary, formed in most cases by the phase γ + γ’. Identical conclusion was drawn from the EDX analysis about chemical compo-

Fig. 3: SEI; magn. 1600x



sition of the MX phase with precedent variant of annealing in case of mutual substitution of Ta and Ti. In case of the phase rich in chromium the substitution is also similar to the first variant. If the ratio between W and Cr is in the first case approx. 20% vers. 42%, then in the second case this ratio was slightly modified to 9% vers. 60%. In this case, too, it is possible to accept for guidance the possibility of mutual substitution between W and Cr, when Mo content, which is around 25% was not fundamentally changed. In case of inter-metallic phase Ni3(Ti, Al) it is possible to accept certain possibility of mutual substitution for Ta and Al, similarly as in the case of the first variant of heat treatment.

CONCLUSION The presented paper summarises the basic data about structural-phase characteristics of the Ni-super-alloy INCONEL 792-5A alloyed in a complex manner after high-tem exposition at the temperature of 900°C during 103 and 2.103 hours. Apart from basic micro-structural char-

Fig. 4: BEI; magn. 1800x

acteristics and observation of potential places for formation of minority phases a detailed EDX analysis of possible chemistry of the segregated minority phases was made. We performed also an analysis of re-distribution of atoms of alloying elements in formed co-existing phases. In many cases certain mutual substitution of alloying elements was observed, which represents important technical parameter and physical engineering background for estimation of the type of precipitating phases, as well as for estimation of possible stability of the given Ni-super-alloy. The obtained findings represent undoubtedly useful data from the viewpoint of technical application of the superalloy INCONEL 792-5A.

ACKNOWLEDGEMENTS This work was realized under the support of the research project No. MSM 619890013 (Ministry of Education of Czech Republic) and projects No. SI - IM5/001 and No. FT-TA3/072 (Ministry of Industry and Trade).

Literature 1. W.ROSS, E., SIMS, C.T.: Superalloy II, Jon Wiley and Sons, 1987, 97. 2. SEO, S.M., et.al.: Met.and Mat.Transactions, 38A, 2007, 883. 3. SAUNDERS, N., et.al.: Modeling the Material Properties and Behaviour of Ni-based Superalloys. In:Superalloys 2004. Ed.Green, A., K. et. al., TMS, Warendale, 2004, p. 849. 4. PODRÁBSKÝ, T., PETRENEC, M., HRBÁČEK, K., MUSIL, V., JONŠTA, Z.: The Structure Changes of Cast Nickel Super Alloy at the Loading Process. Inter. Conf. “Trends in the Development of Machinery and Associated Technology“, TMT 2003, p.253, Lloret de Mar.

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RIM STRESS DISTRIBUTION OF THIN-RIMMED GEAR

G. Marunić

Abstract The paper deals with the effects of rim and web thickness on the rim stress of external spur thinrimmed gear with middle web arrangement. Based on the FEM calculations, the area of maximum rim stress detected in axial direction i.e. at the joint of rim and web, is established in radial direction. The obtained insight into variation of location and magnitude of maximum rim stress in relation to a gear geometrical parameters that contribute to possible gear weight reduction, can be the basis for some additional design directions of gears with complex body.

Key words spur thin-rimmed gear, FEM, rim stress, web thickness

T

he thin-rimmed gears have become more attractive and widely used, and therefore they have been the subject of numerous investigations related to the state of stress in a toothroot area and its reliable determination [1, 2, 3]. Thin rim deformation causes considerable increment of compressive stress while tensile stress increases too, but not so severe. Consequently, fatigue condition of thin-rimmed gear differs from a solid one and critical tooth section may not be at maximum tensile stress position assumed for a solid gear. The evaluation of the load-carrying capacity of tooth-root was improved in analytical procedures proposed by the standards, by including a stress modifying factor that takes into account the contribution of thin rim to a tooth-root bending stress.

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The application of gears with such geometry have to be well founded considering that when the rims are too thin a reduction of fatigue life due to the increased tooth-root stresses can occur and also, fatigue cracks that begin in the root fillet may propagate across a tooth or which is more undesirable, into the rim. The research into the stresses of other parts of thin-rimmed gear structure i.e. a rim, web and hub, has been not so intensive but has led to some useful results that can be utilised for gear dimensioning [4, 5, 6]. The research results in [7] pointed out that for thin-rimmed gear with offset web structure, the stresses existing in the joint of thin rim and web become much greater than the tooth-root stresses. Therefore, the joint stress is proposed to be critical stress point additional to the tooth-root stress when gear strength is evaluated.

In this paper the effects of rim and web thickness on the rim stress of spur thin-rimmed gear with middle web arrangement, are investigated. Additionally, the obtained maximum equivalent stress at the tooth-root and rim are compared. The variation of maximum rim stress area that appears at the joint of rim and web is established in radial direction for different rim and web thicknesses.

3D FEM CALCULATIONS The stresses of thin-rimmed spur gears are calculated by use of 3D FEM and software package I-DEAS. The geometry and the adopted bound-

ary conditions of the applied numerical model are described in [8]. This pinion-wheel model assures the simulation of load distribution along the tooth face width resulting from actual gear geometry and takes into account the deformations at every part of gear structure. A solid pinion and thin – rimmed wheel with middle web arrangement that are utilised for calculations, are standard involute ones with the same tooth geometrical parameters (Tab. 1). The wheel stresses are determined for the engagement position at the outer point of single pair tooth contact.

Number of teeth

z1=z2

20

Rim thickness

sR

30; 20; 15; 10 [mm]

Module

m

10 [mm]

Web thickness

bs

40, 30, 20, 10 [mm]

Pressure angle

α

20 [°]

Material

Module of elasticity E

2.1·105 [N/mm2]

Profile shift coefficient

x1= x2

0

properties

Poisson`s ratio ν

0.3

Face width

b

100 [mm]

Load per unit face width

Fbn/b

100 [N/mm]

Tab. 1: Spur gear pairs data

The values of rim thickness sR expressed by the backup ratio sR/ht (ht – tooth height) are adopted that slightly overcome upper and lower limit proposed by the standard ISO [9]: sR/ht= 0.44; 0.67; 0.89 and 1.33. The web thickness bs expressed by a tooth face width b, covers the range of interest: bs/b = 0.1; 0.2; 0.3 and 0.4. Based on the FEM calculations, equivalent von Mises stress at the inner rim surface is separated.

MAXIMUM TOOTH-ROOT AND RIM STRESS The comparison of maximum equivalent toothroot stress regardless of its location along the tooth face width and along the fillet, and maximum rim stress in relation to axial and radial direction, is performed in order to examine the possibility that maximum rim stress overcomes maximum tooth-root stress.

sR/ht Fig. 1: The comparison of maximum equivalent tooth-root and rim stress

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In Fig. 1 maximum equivalent tooth-root stress σ teqmax on tensile side of the loaded tooth and maximum equivalent rim stress σReqmax are related to the rim and web thickness. It is obvious that the rim stress of the considered gear structure doesn’t overcome the corresponding tooth-root stress. Maximum rim stress approaches mostly to maximum tooth-root stress in the case of the thinnest rim and web, when the deviation of rim stress from the tooth-root stress is about 38%. Maximum equivalent toothroot stress is less influenced by the rim and web thickness, especially by the web thickness.

AREA OF MAXIMUM RIM STRESS IN RADIAL DIRECTION Equivalent rim stress at the inner rim surface has its maximum value at the joint of rim and web. Therefore, maximum rim stress area is established in radial direction considering this location. The rim stress σreq location is expressed by the angle φ measured from the centre line of the loaded tooth towards its compressive side. Maximum rim stress area is developed by use of ten values of angle φ that cover the location where rim stress (at the joint of rim and web) reaches its maximum value. Fig. 2 a, b, c, d shows in detail the distribution of maximum rim stress obtained in axial direction in the range of angle φ within maximum stress value occurs. These

Fig. 2: The distribution of equivalent rim stress at the joint of rim and web in radial direction related to web thickness and for different rim thickness (a) – (d)

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stress distributions are presented in relation to the web thickness bs/b, and separately for certain rim thickness i.e. Backup ratio sr/ht. The rim stress distribution is related to the rim and web thickness in Fig. 3, in the form of contour plot. For the greatest angle φ i.e. For the mostly shifted stress location from compressive side of the loaded tooth towards the adjacent one, the location of maximum stress area is clearly shaped near the thickest rim and thicker web. The web thickness influences the rim stress magnitude mostly for the thickest rim: maximum rim stress increases with the decrement of web thickness for about 97% for the thickest rim, and for about 28% for the thinnest one. The variation of maximum rim stress for certain web thickness is mostly expressed for the thickest web, when the stress for the thinnest rim is more than two times greater than the stress for the thickest rim. It can be noticed that maximum rim stress σReqmax location is shifted mostly from the centre line of the loaded tooth towards compressive side for the thickest rim and thicker web, and maximum rim stress appears under the adjacent tooth. Considering the stress magnitude, the mentioned stress locations characterise the lowest stress values in relation to thinner rims. As the rim thickness decreases the peak of rim stress is more obvious with its area closer to the loaded tooth.

CONCLUSIONS Maximum equivalent rim stress at the joint of rim and web for thin-rimmed gear with middle web arrangement approaches but doesn’t overcome the corresponding maximum tooth-

Fig. 3: The contour plot of maximum rim stress area in radial direction expressed by the angle φ, related to the rim and web thickness

root stress on tensile side of the loaded tooth. In comparison with maximum tooth-root stress, maximum rim stress is much more influenced by both, the rim and web thickness. By the decreasing rim rigidity, the area of rim stress at the joint of rim and web occurs closer to the loaded tooth with more obvious peak value. The contribution of web thickness increment to the gear body rigidity always results with the decreasing rim stress and this intensifies as the rim thickness increases. The research results pointed to the need of careful approach that considers actual gear structure when the strength of gear with complex body is evaluated.

Literature 1. EIFF, H., HIRSHMAN, K. & LECHNER, G.: Trans. ASME: J. Mech., Transmiss. And Autom. Des., 112, 1990, 575. 2. BARET, C. et al.: In: Proceedings of International PowerTransmissions and Gearing Conference. 1989, Chicago, USA: ASME, 173.

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3. BIBEL, G. D., Reddy, S. K. & Savage, M.: Technical Report 91-C-015. 1991, NASA. 4. KIM, H.C. et al.: In: Proceedings of International Congress -Gear Transmissions ´95, 1995, Sofia, Bulgaria: TUME-Bulgaria, 164. 5. SAYAMA, T., ODA, S. & UMEZAWA, K.: Bulletin of JSME, 246, 1985, 3025. 6. LINKE, H., MITSCHKE, W. & SENF. M.: Machinenbautechnik, 32, 1983, 450. 7. LI, S.: Journal of Mechanical Design, 124, 2002, 511. 8. MARUNIĆ, G., In: Proceedings of 5th International Scientific Conference RIM 2005, 2005, Bihać, Bosnia and Herzegovina, University of Bihać. 9. ISO 6336 - 3, Calculation of load capacity of spur and helical gears - Part 3: Calculation of tooth bending strength, 2006.

MECHANICAL DESIGN OF THERMOPLASTIC SHELLS OF SMALL WASTEWATER TREATMENT SYSTEMS

O. Šuba, J. Jurčiová

Abstract Some aspects of structural design of small wastewater treatment plastic containers are considered in the paper. Implementations of welded thermoplastic shell vessels are connected by certain problems caused by generally insufficient flexural stiffness of thermoplastics walls of thin-walled structures in cases of external backfill loads. As it is shown, low wall stiffness causes not only high values of displacements, but predispositions to loss of stability of a construction at first. Influences of geometrical parameters and reinforcements of the shell on the level of buckling safety factor are studied with support of FEM analyses.

Key words thermoplastic shell, stability, buckling, FEM

T

hermoplastics sink into many industrial segments and pace of their applications is increasing. It is because, that classic materials are

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not fulfilling increasing technical needs. Without modern materials series of innovating processes would not be performed. Specific properties

of thermoplastics together with new processing and software technologies opens wide possibilities of applications in variety of regions. Every successful application of thermoplastics is conditioned beyond consistently construction and technological preparation also with qualified determination of dimensions and shapes of projected construction. Thermoplastics are in general less stiff and tough, have significant inclination to flow, high coefficient of thermal expansion and significant dependence of mechanical properties on temperature. These properties are in general disadvantageous. On the other side are unquestionable positives – easy processing, low energetical demandingness and high productivity of manufacture or wide possibilities of new technologies. In at least order important is also resistance against aggressive stuff and environments, which thermoplastics specialize for building of devices, working in hard conditions of operations, with example in chemical and food industry.

STABILITY OF CYLINDRICAL SHELLS OF WTS Cylindrical shells of small WTS vessels are maked of thin walled cylindrical shells with inner structure, divide volume of cleaner on single sections. Outer reinforcement is then maked of set-up of perpendicular and circumferential reinforcement sheets. Working load is given by superposition of inner hydrostatic pressure with certain height of water level and outer pressure of external backfill loads. In Fig. 1 is shown typical construction of small WTS. Water level achieves some height, practically to height level of inner structure. Height of of external backfill loads achieves mostly the height of top part of vessel. Norm EN 12 566 define backfill loads pressure curve in direction of height as linear. In basic operating state of load, inner hydrostatic water pressure and outer pack pressure is compensating.

FEM MODELING OF COV SHELL STABILITY Analytical solutions of inner pressure determination in stability loss are known of plain cylindrical homogenous and isotropic or orthotropic shells, loaded with radial outer pressure. These solutions allow determination of critical loading by stability loss of unreinforced sectors between solid reinforced ribcage [1]. They also allow verifications of FEM results. Fig. 1: An example of construction of small WTS

Specification of thermoplastics mechanical behaviour includes specialities and problems in process of propose beside classical constructions. Technology character and effort of mass decreasing, price leads to that construction of thermoplastics are mostly proposed as thin walled. Despite it, ratio of stiffness to strength, is in thermoplastics greatly low, so in series of examples is for product propose definitive state of deformation, not only carrying capacity. Often can be for propose definitive marginal states, having cause of construction stability loss.

In cases, when on cylindrical shell the elements of inner structure are welded, or the series of reinforced inner circumferential and axial reinforcements is used, FEM modeling is needed to use. Result of computation of linear stability of shell construction is theoretical value of so called critical load, which correspond to transition between stabile and labile steady-state of construction (indifferent steady-state at critical load). Critical load is in general upper estimation of construction stabile capacity. From final values of critical loads results relative small, practically negligible influence of vertical bar of outer

82

structure on stability of outer shell. Similar also vertical inner reinforcements don’t markedly contribute to increase of stabile capacity. From this look, are most efficiency outer welded circumferential cart-ladder. This are in many applications declined because of their consumption, thus their easy vulnerability in process of drycleaner installation. Used are they then mostly reinforced with circumferential straps, with thickness corresponding to that of bowls coating.

Fig. 2: Stability of a cylindrical shell reinforced by circumferential strap of thickness 8 mm, width 100 mm, placed in optimal height. Safety in critical load is 1.94

On Fig. 2 is shown result of stability analysis of a shell, especially with circumferential strap reinforcement in height of maximal reinforcement effect. Reinforcement increase value of safety to critical load from 1.56 to 1.94. Dependence of obtained safety on height is shown on Fig. 3. As one can see, optimal height is 60 % of bowl height.

Fig. 3: Dependence of safety on stability limit on position of strap reinforcement of thickness 8 mm and width 100 mm

Fig. 4: Thickness and width of strap reinforcement influence on stability of cylindrical shell: a - 100 x 8 mm, b - 150 x 8 mm, c - 150 x 10 mm. Safety a/b/c : 1.9 / 2.21 / 2.35

83

On Fig. 4 is shown influence of dimensions of strap reinforcement on coefficient of safety and corresponding own shape of shell aberration, at identical height of reinforcement placement.

CONCLUSIONS According to small values of bending stiffness of walls welded shell constructions from thermoplastic and their dependence on load period and temperature at their practical applications real danger of marginal state of stability loss of thinwalled shell is possible, resulting in abrasion and

total destruction. As it results from this article, it is necessary to give problematic of thermoplastic shells stability in their construction propose enhanced attention. With that we can prevent of their possible luck success in practical applications of this types of construction.

ACKNOWLEDGEMENT Article was prepared thanks to project MSM 708 352 102.

Literature 1. PADOVEC, J.: In Proceedings of the 24th International Scientific Conference Reinforced plastics 2007, Karlovy Vary, Czech Republic, Dům techniky Plzeň, 22.-24. 5, 2007. p. 37-42. ISBN 97880-239-8857-4.

PLASTIC FORMING OF ECAP PROCESSED EN AW 6082 ALUMINUM ALLOY

M. Greger, L. Kander, B. Kuřetová

Abstract Microstructural development of aluminium alloy 6082 during equal-channel angular pressing was investigated to understand the mechanisms of grain refinement and strain accommodation. The samples were extruded at room temperature. Cross-section of original samples was 8 x 8 mm and their length was 32 mm. Deformation forces were measured during extrusion, resistance to deformation was calculated and deformation speed was determined approximately. Analysis of structure was made with use of light microscopy and SEM. Mechanical properties of samples after extrusion were determined by tensile test and by so called penetration test.

84

Key words ECAP, aluminum alloy 6082, microstructure

E

xtrusion by ECAP method enables obtaining of a fine-grain structure in larger volumes. Products made by this technique are characterised by high strength properties (Fig. 1), and they can be potentially used at subsequent super-plastic forming. Magnitude of deformation, development of structure and resulting mechanical properties achieved by this technique depend notably on: homologous temperature Th, size of grain dz, deformation speed ε·, homologous tension in die (σ/E), density of structural failures, on purity, etc. Obtaining of the required final structure depends primarily on geometry of tool, number of passes through die, obtained magnitude and speed of deformation, temperature, etc. 4

the internal energy gain differs at different places of formed alloy [2]. For example the value of internal energy is different in slip planes, at boundaries and inside cells. It is possible to observe higher internal energy also in proximity of precipitates, segregates and solid structural phases. For usual techniques, pure metals, medium magnitude of deformation and temperatures the value of stored energy is said to be approx. around 10 J.mol-1 [3]. At cold extrusion density of dislocations increases with magnitude of plastic deformation. Density of dislocations depends linearly on magnitude of plastic deformation in accordance with the well-known equation [4]: ρ = ρ 0 + K · ε

(1)

where ρ0 is initial dislocation density, K is a constant, ε is magnitude of deformation.

Hardness

Flow stress necessary for continuation of deformation is function of number of lattice defects [5]: 1



(Grain Size).%

τ = τ0 + k · G · b · ρ 2

(2)

where τ0 is initial flow stress, k is a constant, G, b is modulus of elasticity in shear and Burgers’ vector.

Fig. 1: Predicted dependence of strength on grain size [1]

DEVELOPMENT OF STRUCTURE Influence of magnitude of plastic deformation on properties of metallic materials is connected with increase of internal energy. Internal energy increases right to the limit value, which depends on manner of deformation, purity, grain size, temperature, etc. As a result of nonhomogeneity of deformation at ECAP technique

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eXPERIMENTAL PROCEDURE The objective of experiments consisted in verification of deformation behaviour of the given alloy, determination of resistance to deformation, formability and change of structure at extrusion of alloys. Experiments were made with use of an apparatus, the diagram of which is shown in Fig. 2. Contents of individual elements in the alloy are given in the Tab. 1.

Fig. 2: Diagram of extrusion ECAP



Fig. 3: Structure of initial sample

Contents of elements

Mg

Si

Mn

Fe

Ti

Cu

Zn

Ni

Sn

Cr

[%]

1.106

0.88

0.9

0.21

0.003

0.029

0.026

0.003

0.003

0.002

Tab. 1: Chemical composition of the aluminium alloy 6082

Microstructure Structure of initial original samples is shown in Fig. 3 and structure of samples after individual passes is shown in Fig. 4. The structure contains ordinary inter-metallic phases corresponding to the given composition of the alloy. Average grain size in transverse direction was determined by quantitative metallography methods and it varied around 150 μm. Change of shape of the front and rear end of the sample and maintenance of integrity at individual stages of extrusion depends on level of lubrication and on radii of rounding of edges (Rv, Rvn) of extruding channel [6]. After individual passes there occurred accumulation of deformation strengthening, the basis of which was in the formed sub-structure, which can be seen in the Fig. 5 taken by an electron microscope. Deformation forces were measured during extrusion and pressures in the die were calculated. At extrusion with the radius of rounding of edges (Rv = 2 mm; Rvn = 5 mm) the pressure in the die varied at the 1st pass around τmax = 620 MPa, and it gradually increased in such a manner that at the fourth pass its magnitude was approximately τmax = 810 MPa. At extrusion

through a die with smaller radii of rounding (Rv = 0.5 mm; Rvn = 2 mm) the pressure at the first pass was approx. τmax = 780 MPa, and at the third pass it was approx. τmax = 1560 MPa [7] Significantly higher values of resistance to deformation and strengthening at extrusion are related to high absolute value of octahedral stress, which either contributes to more difficult formation of dislocations or decelerates their movement. Strengthening can be described in several manners. Grain boundaries have very distinct impact. Influence of the grain radius dz on yield strength is usually described by Hall-Petch relation:



(3)

For the aluminium alloy of the type similar to the alloy 6082 the constants in the equation (3) vary around these values: σ0 = 15,2 MPa; Ky = 2,35 N.mm-3/2. Another factor, which influences significantly flow stress and development of microstructure is the angle φ, which is formed by axis of vertical and horizontal channel. This angle determines magnitude of shearing strain in individual passes and it can be expressed by the relation:

86



γ = 2 cotg(φ/2)



(4)

Shearing strain at the angle φ = 90 achieves the value 2 and normal deformation the value 2.3. Smaller angle φ leads to higher shearing stress at each pass. We have checked the size of the angle φ in the range from 90o to 125o with use of technological route BC, Fig. 6. We have ascertained, that refining of grains is the most efficient (under the same magnitude of deformation), at the angle of 90o. This is given by the fact that two slip planes in the sample

make in this case the angle of 60o. For materials, forming of which is more difficult, it is more advantageous to apply the angle φ= 120o together with higher extrusion temperature. It is possible to calculate the magnitude of accumulated deformation from the relation:

ε = 2N/√3.cotg(φ/2)



(5)

where N is number of passes through a die. After passes we achieve in the sample magnitude of total accumulated deformation, Tab. 2.

Number of passes

Total Strain Intensity [ε]

Equivalent Area Reduction [%]

1

1.15

69

2

2.31

90

3

3.46

97

4

4.62

99

Tab. 2: Effective strain intensity and equivalent reduction [6]

a) b) c) Fig. 4: Structure of samples after extrusion in longitudinal direction: a) after the 1st pass, b) after the 2nd pass, c) after the 3rd pass

Mechanical properties determined by tensile test We have verified influence of rectangular extrusion on mechanical properties with use of classical mechanical tensile test and so called penetration test. We made from samples after application of the ECAP technique miniature test specimens for tensile test (Fig. 7), which were tested at the laboratory temperature and speed of movement of process speed 10 mm/ min.

87

Obtained values of strength properties varied for the alloy 6082 within the range Rm = 220 to 230 MPa. Obtained strength values correspond very well with the values obtained by simulation and the values calculated on the basis of the hardness tests. In the frame of evaluation of influence of the ECAP technique of mechanical properties we have made also tensile tests of investigated materials, but without application of the ECAP technique. We have tested altogether 4 test specimens with cross-section 2.5 x 5 mm. On the basis of realised experiments

we have determined ultimate strengths, which for the alloy 6082 were Rm = 175 MPa. As it follows from comparison of strength properties as a result of rectangular extrusion the strength of the alloy 6082 was increased approximately by 25 %. We have performed a fracture analyses on broken halves of test specimens. Results of these fracture analyses, including their graphical presentations are given below.

Mechanical properties determined by penetration test Taking of material samples for experiment was made by the apparatus SSamTM- made by RollsRoyce [8]. We made from the samples after application of the ECAP technique three test speci-

mens in the form of disc with diameter of 8 mm and thickness of 0.5 mm, which were subjected to the penetration test at laboratory temperature. Basic mechanical properties were determined on the basis of penetration test, the principle of which consists in penetration of special punch with spherical surface through the flat disc-shaped sample, which is fixed between the upper holder and the lower die. On the basis of realised experiments it is possible to state that strength properties of the alloy 6082 obtained by penetration test vary in the range from Rm = 250 to 260 MPa, which demonstrates very good conformity with values of strength properties obtained by classical tensile test (Rm = 220 to 230 MPa).

Fig. 5: Substructure aluminium alloy 6082 after extrusion: a) after the 1st pass, b) after the 2nd pass, c) after the 3rd pass, d) after the 4th pass

Fracture analysis of fracture areas in the alloy 6082 Analysis of fracture areas was made with use of scanning electron microscope JEOL – JSM 5510. From visual viewpoint the fracture area looked as planar and fine-grain with indistinctive shear fractures. It was determined by detail microfractographical observation that fracture area

Fig. 6: The technological route

88

was formed exclusively by mechanism of transcrystalline ductile failure with morphology of various pits, Fig. 8a. These cavities contained big number of minuscule particles, Fig. 8b, 8c (→).

CONCLUSIONS We have verified experimentally behaviour of the alloy 6082 after extrusion. Method ECAP is a potential tool for refining of grain in polycrystalline metals. This procedure makes it possible to obtain after 4 passes the grain size of approx. 1 μm. In order to obtain an optimum micro-structure it is necessary to apply more passes with turning of the sample between individual passes by 90° about the longitudinal axis. After 4 passes there occurs development of sub-structure. At use of the die with the angle of 90° there is achieved more intensive deformation and resistance to deformation is higher than at extrusion with higher angles.

a)

Fig. 7: Miniature test specimens for tensile test

Radii of rounding of working edges of extruding channel must correspond to conditions for laminar flow of metal.

ACKNOWLEDGEMENT The works were realised under support of the Czech Ministry of Education project VS MSM 619 891 0013.

b)

c)

Fig. 8: Fracture areas

Literature 1. SEGAL, V. M.: Mat. Sci. and Eng., A197 (1995), 157. 2. LUKÁČ, P., TROJANOVÁ, Z. The influence of grain size on the deformation behaviour of selected Al alloys. NANO ´06. VUT Brno, 2006, 57. 3. Comaneci, R. Processing of aluminum and Al-Mg alloys by severe plastic deformation. Metal 2008. Tanger. Ostrava 2008, 37.

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4. FUJDA,M., KVAČKAJ,T. Effect of severe plastic deformation on the structure and mechanical properties of EN AW 6082. Proceedings of 5th International conference Aluminium 2007. Alcan Děčín Extrusions 2007,274. 5. ZRNÍK, J. CGP forming method to produce ultrafine grained structure in aluminium. Metal 2008. Tanger. Ostrava 2008, 48. 6. GREGER, M., KOCICH, R. In 6th Scientific-technical conference Material in engineering practice´05. TU Žilina, Herľany 2005, 85. 7. GREGER M. et al. Possibilities of aluminum extrusion with use of a the ECAP method. Proceedings of 9th International conference Aluminium in Transport 2003. Institut of Non-Ferrous Metals. Cracow-Tomaszowice 2003, 165. 8. GREGER, M., KOCICH, R., ČÍŽEK, L., MUSKALSKI, Z. Mechanical properties and microstructure of Al alloy produced by SPD process. Proceedings of 10 th International research/expert conference TMT 2006.Universitat politecnica de Catalunya. Barcelona 2006, 253.

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