Selected Mechanical Properties of PETG 3-D Prints - Science Direct

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ScienceDirect Procedia Engineering 177 (2017) 455 – 461

XXI International Polish-Slovak Conference “Machine Modeling and Simulations 2016”

Selected mechanical properties of PETG 3-D prints Ksawery Szykiedans*, Wojciech Credo, Dymitr Osiński Faculty Of Mechatronics, Warsaw University of Technology, ul. Boboli 8, 02-525 Warszawa, Poland

Abstract The 3D printing is a way of additive manufacturing that allows the creation of sophisticatedly shaped bodies at relatively low cost and in short time span. It is especially useful for rapid manufacturing, including engineering applications such as rapid prototyping. The commonly used fused deposition modelling (FDM) method dispenses filament from heated nozzle positioned in three axes that hardens after exiting the nozzle. This article presents the research focused on the mechanical properties (mainly the basic tensile strength and elastic modulus) of elements printed using the FDM method, made of two distinctive materials: polyethylene terephthalate glycol (PETG) without additions and glass-fiber reinforced PETG. The paper outlines strengths and weaknesses of the materials described and compares the properties of PETG with and without the addition of glass fiber. The gathered data helps to quantify the mechanical properties of parts made of PETG and may also be used for modelling the properties of 3D printed elements. © 2017 2017The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license © Published by Elsevier Ltd. This Peer-review under responsibility of the organizing committee of MMS 2016. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MMS 2016 Keywords: 3-D prints; tensile modulus; Zortrax filaments; FDM mechanical properties;

1. Introduction The following paper continues the research started in 2015 [1], focusing on the mechanical properties of elements/parts printed using the FDM method. As it was stated before producers are publishing data about the materials they use in their printers, but in most cases the data-sheets are incomplete or sometimes they are not available. That fact and strong anisotropy of 3D prints causes a need of experimental verification of mechanical properties of the prints especially when new material is introduced in market. It is very important for the authors because of the fact of supervising 3D printing laboratory used by students. Presented paper consist a first try-out of authors to measure mechanical properties of polyethylene terephthalate glycol used as FDM filament (Z-PETG

* Corresponding author. Tel.:+48 22 234 8333; fax: +48 22 234 8602. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MMS 2016

doi:10.1016/j.proeng.2017.02.245

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Ksawery Szykiedans et al. / Procedia Engineering 177 (2017) 455 – 461

produced by Zortrax company). Previously this kind of material was used only with addition of glass fiber and being used as filament named Z-GLASS due to its translucence. 2. Specimens Test procedure described in ISO 527 standard was selected for preparation of specimens used in testing of mechanical properties of 3D prints and test procedure itself. ISO 527-2 defines specimen types to be used for tensile tests. They are; types 1A (A1) and 1B (A2) are standard specimen for comparable data, types 1BA (A22) and 1BB (A25) for reduced-scale specimen, types 5A and 5B which are proportional to ISO 37, types 2 and 3 (only informative annex), types CW and CP as small tensile specimen for heat ageing tests. Type 1A was used as main specimen type and prints of different thickness (1 and 5 mm) made of Z-PETG were made. Due to limited ability of Zortrax M200 to print very high and slender specimens type 5A was chosen to prepare flat and upright printed specimens. S.-H. Ahn at al. [2] as well as C.Wendt at al. [3] have pointed that dumbbell specimen designs are unsuitable for mechanical testing, as the nonparallel fused beads may cause stress concentrations away from the specimens’ gauge area. That statement is true in a case when printing head track is a spiral-like or labyrinth-like line or any other contour style tool-path [4]. Zortrax postprocessor used by authors generates raster type print infill in a form of crossed lines (Fig. 1). Due to this feature, it is plausible that breaking lines will cover filament beads and an air gaps between filament beads will cause stress concentration.

Fig. 1. 3D models of 1A and 5A type specimens post-processed in Zortrax printer software.

Six series of specimens were prepared (Table 1), they were printed with use of Z-PETG filament – the new material and as reference with use of Z-GLASS filament. Prints were prepared in 1A and 5A type having thickness of 5 millimetres. One series (P3) was prepared as 1 millimetre thick and series P4 was printed in upright direction.

Ksawery Szykiedans et al. / Procedia Engineering 177 (2017) 455 – 461 Table. 1. Specimens series descripcions and specifications Series code

Specimen type

Specimen material

Print direction

G1

5A 5 mm thick

Z-GLASS

flat

G2

1A 5 mm thick

Z-GLASS

flat

P1

5A 5 mm thick

Z-PETG

flat

P2

1A 5 mm thick

Z-PETG

flat

P3

1A 1 mm thick

Z-PETG

flat

P4

5A 5 mm thick

Z-PETG

upright

3. Test procedure As well as in specimen design there is no standardized test procedure intended to be used with Additive Manufacturing parts yet. Specific standards are being prepared by both ISO and ASTM [5]. Author decided to follow well known procedure so test procedure was also adopted from ISO527-2 standard. For the measurement of value of modulus of elasticity, the speed of testing was set as 1 mm/min ad it was held until relative extension reached 0,25%. Then speed was increased to 50 mm/min to get a specimen break (Fig. 2.).

Fig. 2. Change of elongation speed during testing.

4. Test results Experimental data have been obtained from MTS Bionix 270 test rig. The tensile modulus was calculated between 0.05% and 0.25% strain. It was calculated by a linear regression calculation. Then mean value and median was calculated for every of specimen series.

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Fig. 3. Z-Glass specimens series G1 test results.

Fig. 4. Z-Glass specimens series G2 test results.

Fig. 5. Z-PETG specimens series P1 test results.





Specimens behavior in general was similar to known in literature [6] but there are some aberrations. Specimens P1-5 and P1-7 had lowest values of Young’s modulus but they load capability was larger. Series P3 was printed 1 mm thick. This series shows widest range of results. This is typical or low thickness prints were even single disturbance in structure can cause heavy concertation of stress. Last series P4 was printed upright and it was very

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vulnerable especially for normal and bending forces. Only 3 of 10 specimens were tested properly, other broke during printing or when were clamped in testing rig. 4. Summary Conducted test have showed that 3D prints are anisotropic and all series have different values of tensile modulus (Table 2). Values are even different between specimens made of the same material G1,G2 and P1, P2, P3,P4. Table. 2. Tensile modulus of a tested 3-D printers materials Z-GLASS and Z-PETG. Material Specimen

Mean value of tensile modulus (MPa)

Experimental values of tensile modulus

minimum (MPa)

maximum (MPa)

Z-GLASS, Flat printed [1]

734

721

764

Z-GLASS, Upright printed [1]

1436

1378

1477

G1 series Z-GLASS, Flat printed

665

619

682

G2 series Z-GLASS, Flat printed

368

358

389

P1 series Z-PETG, Flat printed

594

392

688


458

434

468


650

539

728

P4 series Z-PETG, Upright printed

910

862

942

Received differences between Young’s modulus value are effect of presence of air gaps in print structure and stress concentration along filaments beads. These two phenomena cause crack surface area being different than calculated as area of gauge cross-section (Fig. 9).

Fig. 9. Z-PETG specimens crack area – series P1 left, P2 right.

The only specimens that cracked perpendicularly to its four walls was series P4. In that case cracking, can be analyzed as delamination of two fused layers (Fig.10)


Fig.10. Z-PETG specimens crack areas – Series P4 printed upright – clear flush crack.

Conducted works and tests proved specimen break area location is hard to be precisely pointed before a test. On the other hand, FDM printed specimens are more product samples than material specimens in the meaning of i.e. ISO 527 standard. That fact and presented difficulties of upright prints testing forced author to start development of new kind of specimen intended to test upright prints – mainly to determine delamination force and Young’s modulus in direction perpendicular to printing base in FDM printers. References [1] K.Szykiedans, W. Credo, Mechanical properties of FDM and SLA low-cost 3-D prints, Procedia Engineering, 136 (2016) 257-262. [2] S. H. Ahn, M. Montero, D. Odell, S. Roundy, P. K. Wright, Anisotropic material properties of fused deposition modeling ABS, Rapid Prototyping Journal, 8(4), 2 (2002) 48-257. [3] C. Wendt, M. Batista, E. Moreno, A. P. Valerga Fernández-Vidal, S. R., O. Droste, M. Marcos, Preliminary design and analysis of tensile test samples developed by Additive Manufacturing. Procedia Engineering, 132 (2015) 132-139. [4] A. Bellini, S. Güçeri, Mechanical characterization of parts fabricated using fused deposition modeling. Rapid Prototyping Journal, 9(4) (2003) 252-264. [5] M. D. Monzón, Z. Ortega, A. Martínez, F. Ortega, Standardization in additive manufacturing: activities carried out by international organizations and projects. The international journal of advanced manufacturing technology, 76(5-8) (2015) 1111-1121. [6] J. Martinez, J. L. Dieguez, J. E. Ares, A. Pereira, J. A. Perez, M. Marcos, J. Salguero,. Modelization and structural analysis of FDM parts. In AIP Conference Proceedings-American Institute of Physics, 1431, 1, 2012, pp. 842.

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