experimental test of composite material for sandwich

A Dissertation Report on

EXPERIMENTAL TEST OF COMPOSITE MATERIAL FOR SANDWICH PANEL Submitted by DIPAKKUMAR G. VAMJA In partial fulfillment for the award of the Degree of MASTER OF TECHNOLOGY IN MECHANICAL ENGINEERING (MACHINE DESIGN)

Under the guidance of PROF. GHANSHYAM G. TEJANI (Assistant Professor)

DEPARTMENT OF MECHANICAL ENGINEERING SCHOOL OF ENGINEERING, RK UNIVERSITY, RAJKOT, GUJARAT-360020

JUNE 2013

DECLARATION OF ORIGINALITY

I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which has been accepted for the award of any other degree or diploma of the university or other institute of higher learning, except where due acknowledgment has been made in the text. Furthermore, to the extent that I have included copyrighted material that surpasses the bounds of fair dealing within the meaning of the Indian Copyright Act, I certify that I have obtained a written permission from the copyright owner(s) to include such material(s) in my dissertation report and have included copies of such copyright clearances to my appendix. I declare that this is a true copy of my dissertation report, including any final revisions, as approved by my dissertation report review committee.

Place: RAJKOT

Signature:

Date: Name: DIPAKKUMAR G. VAMJA Enrollment No.: 11SOEMD21013

DEPARTMENT OF MECHANICAL ENGINEERING

ii

CERTIFICATE

This

is

to

certify

that

the

dissertation

report

entitled

“EXPERIMENTAL TEST OF COMPOSITE MATERIAL FOR SANDWICH PANEL” submitted by MR. DIPAKKUMAR G. VAMJA to the School of Engineering, R K University, Rajkot towards partial fulfillment of the requirements for the award of the Degree of Master

of

Technology

in

MECHANICAL

ENGINEERING

(MACHINE DESIGN) is a bonafide record of the work carried out by him under my supervision and guidance and is to the satisfaction of department. Date: Place: RAJKOT ____________________________ PROF. GHANSHYAM G. TEJANI (Supervisor) ___________________ PROF. K. D. KOTHARI (Head of Department)

_____________________ DR. C. D. SANKHAVARA (Director)


iii

THESIS APPROVAL This is to certify that research work embodied in this entitled: “EXPERIMENTAL TEST OF COMPOSITE MATERIAL FOR SANDWICH PANEL” was carried out by MR. DIPAKKUMAR G. VAMJA;

11SOEMD21013

at

Department

of

Mechanical

Engineering, School of Engineering, R K University is approved for the partial fulfillment of the degree of Master of Technology in MECHANICAL ENGINEERING (MACHINE DESIGN) by R K University.

Date: Place: RAJKOT

Examiner(s) Name and Signature:

1)

2)

3)


iv

ACKNOWLEDGEMENT

It is indeed a pleasure for me to express my sincere gratitude to those who have always helped me throughout my work. I heartily thank my Guide, Prof. Ghanshyam G. Tejani who greatly helped me in my dissertation work without whose help the work would not have been in the shape what it is. He is a constant source of guidance and inspiration to me. He has been very patient and extended excellent support, never accepting less than my best efforts. I also thank our Head of Department Prof, Kartik D. Kothari, for motivation and valuable guidance. Without whose guideline and motivation I would have not completed my dissertation work. I also thank Director of R K University and Principal Dr. C. D. Sankhavara without whose guideline and motivation I would have not completed my dissertation work. I heartily thank our trustees and dignitaries without whose motivation my dissertation work would not have been in the shape what it is. I am also thankful to all the other staffs of workshop, library and department for their cooperation, help and guidance provides to me for my research work. I am also thankful to my all colleagues for building good team work to make the success of my dissertation work. Last but not the least; I would like to thank God Almighty, My parents, My family members and friends for their love, support and excellent co-operation to build my moral during the work.

Place: RAJKOT

Signature:

Date: Name: DIPAKKUMAR G. VAMJA Enrollment No.: 11SOEMD21013


v

TABLE OF CONTENT Title Page

i

Declaration of Originality

ii

Certificate

iii

Thesis Approval

iv

Acknowledgement

v

Table of Content

vi

List of Tables

viii

List of Figures

ix

Nomenclature

xi

Abstract

xii

Chapter No. 1

Page

Chapter Title

No.

Introduction

1

1.1

Introduction of composite material

1

1.2

Classification of composite materials

4

Summary of differences between steel and composites

1.3

6

construction

1.4

Use of composites in automobiles per year

7

1.5

Introduction of sandwich panel

8

1.6

Structure of a sandwich panel

9

Definition of sandwich composite

9

1.7

Why sandwich panel used?

11

1.8

Components in Sandwich Composites

12

1.8.1

Core

12

1.8.2

Skins

13

1.8.3

Properties of Sandwich Composites

14

1.8.4

Advantages of sandwich panel

15

1.6.1


vi

1.8.5

Limitations of Sandwich Composites

15

1.8.6

Applications of Sandwich Composites

16

1.9

Work Objective

16

1.10

Outline of the Dissertation work

17

Literature review

18

2.1

Introduction

18

2.2

Work done

18

Honeycomb core sandwich panels

26

3.1

Introduction of honeycomb core

26

3.2

Honeycomb structure

27

Definition of the unit cell

28

Material selection for sandwich panel

31

Characteristics of materials for sandwich panel

31

4.1.1

Face materials and its property

31

4.1.2

Core materials and its property

34

4.1.3

Binder materials and its property

38

Experimental set-up and test model of composite material

40

5.1

Experimental set-up

40

5.2

Tensile test of composite material

43

5.3

Bending test of composite material

46

Results and discussion

50

6.1

Tensile test of composite material

50

6.2

Bending test of composite material

55

6.3

Flexural test of composite material

61

7

Conclusion

63

8

Future recommendation

64

Reference

65

Appendix

67

2

3

3.2.1 4 4.1

5

6


vii

LIST OF TABLE

Table No.

Description

Page No.

1.1

Differences between steel and composites construction

06

1.2

Use of Composites in Automobiles per Year

07

4.1

Materials property of aluminium and steel

32

4.2

Materials property of polyethylene core

35

5.1

Sample size and mass for tensile test

43

5.2

Sample size and mass for bending test

46


viii

LIST OF FIGURE

Figure No.

Name of the figure

Page No.

1.1

Light weight composite military helmet

02

1.2

Interior part of the Mercedes A-200 (Generation of A classes)

03

1.3

Classification of composite materials

04

1.4

Geometry of sandwich plate

09

1.5

Structure of a sandwich composite

10

1.6

Honey comb sandwich panel

11

1.7

Illustration of sandwich composite

15

3.1

Honeycomb core

27

3.2

Unit cell for honeycomb core

27

3.3

Reduced unit cell and its parameters

28

3.4

Geometrical parameters for honeycomb core

28

3.5

Unit cell of polyethylene sheet

29

4.1

Aluminium plate

33

4.2

Polyethylene sheet without hexagon

36

4.3

Polyethylene sheet with hexagonal structure

37

5.1

Experimental set-up of Flexural test

40

5.2

Experimental set-ups for tensile and bending test

41

5.3

Universal testing machine

42

5.4

Composite material without hexagon

44

5.5

Composite material with hexagon

44

5.6

Experimental set-up of Tensile test

45

5.7

Preparation of experimental set-up of bending test

47

5.8

Experimental set-up of Bending test

48

5.9

Test piece after bending test

49

6.1

Tensile result generated by UTM (composite material without hexagon)


50

ix

6.2 6.3 6.4

6.5

Tensile result generated by UTM (composite material with hexagon) Comparison of tensile test result Bending result generated by UTM (composite material without hexagon) Bending result generated by UTM (composite material with hexagon)

52 54 55

57

6.6

Comparison of bending test result

60

6.7

Flexural test of composite material

61


x

NOMENCLATURE

a

Cell’s parameter

h

Thickness of the core material

e

Wall’s thickness of tubes or honeycombs

θ

Cell angle

k

Stiffness (N/mm)

E

Young’s modulus of elasticity (N/mm2)

t

Thickness

µ

Poisson’s ratio

L

Length

6u

Ultimate tensile strength (N/mm2)

6y

Yield strength (N/mm2)

ρ

Density of material

F

Load

A

Area


xi

ABSTRACT Automotive industry is on the verge of development. More and more comforts are being incorporated in a vehicle. On other hand customers have stringent demand of fuel economy, high performance at low cost. In order to have high fuel economy the auto-motive manufacturers are induced to reduce weight. In this research work flat plate is selected as a target weight reduction composite material. This can be achieved either using high strength low weight material or by using low weight composite sandwich panel. Aluminium composite (Aluminium skin, polyethylene core, resin binder material) material being light and strong, it is selected as an alternative material by considering peer reviewed papers and industrial guidance. By using this flat plate sandwich panel, tensile strength, bending strength, flexural limit have been carried out for optimization of composite material for sandwich panel construction. Tensile test, bending test is tested on Universal Testing Machine (UTM), at R.K.UNIVERSITY-RAJKOT. One can use sandwich panel composite material to optimize mass and cost of various automobile, marine, aerospace and various structures. Key words: Aluminium and polyethylene plate, binder material, Hexagon structure, sandwich panel composite, Universal Testing Machine (UTM).


xii

CHAPTER-1 INTRODUCTION

1.1 Introduction of composite material The word composite in the term composite material signifies that two or more materials are combined on a macroscopic scale to form a useful third material. The key is the macroscopic examination of a material wherein the components can be identified by the naked eye. Different materials can be combined on a microscopic scale, such as in alloying of metals, but the resulting material is, for all practical purposes, macroscopically homogeneous, i.e., the components cannot be distinguished by the naked eye and essentially act together. The advantage of composite materials is that, if well designed, they usually exhibit the best qualities of their components or constituents and often some qualities that neither constituent possesses [9]. Composite materials have a long history of usage. Their precise beginnings are unknown, but all recorded history contains references to some form of composite material. For example, straw was used by the Israelites to strengthen mud bricks. Plywood was used by the ancient Egyptians when they realized that wood could be rearranged to achieve superior strength and resistance to thermal expansion as well as to swelling caused by the absorption of moisture. Medieval swords and arm or were constructed with layers of different metals. More recently, fibrereinforced, resin matrix composite materials that have high strength-to-weight and Stiffness-to-weight ratios have become important in weight sensitive applications such as aircraft and space vehicles.


Page 1

Composite materials have significantly different physical properties, and thus the composite properties are noticeably different from constituent properties. For example, common metals almost always contain unwanted impurities or alloy elements, plastic generally contain small quantities of fillers, lubricants, ultraviolet absorbers and other materials for commercial reasons such as economy and ease of processing, yet these generally are not classified as composites. Two phase metal alloys are good example of particulate composite in terms of structure.

Figure 1.1 Light weight composite military helmet [6]

Composites offer good impact properties, of aluminium, steel, glass/epoxy, Kevlar/epoxy, and carbon/epoxy continuous fiber composites. Glass and Kevlar composites provide higher impact strength than steel and aluminium. Complex parts, appearance, and special contours, which are sometimes not possible with metals, can be fabricated using composite materials without welding


PAGE 2

or riveting the separate pieces. This increases reliability and reduces production times. It offers greater manufacturing feasibility.

Figure 1.2 Interior part of the Mercedes A-200 (generation of a class) [6]

Composite materials offer greater feasibility for employing design for manufacturing (DFM) and design for assembly (DFA) techniques. These techniques help minimize the number of parts in a product and thus reduce assembly and joining time. By eliminating joints, high-strength structural parts can be manufactured at lower cost. Cost benefit comes by reducing the assembly time and cost.


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1.2 Classification of composite materials

Engineered composites

Particulate

Fibrous

Preffered orientation

Random orientation

Multi layer

Single layer

Hybride laminate

Laminate

Discontinuous & short fibers

Continuous &long fibers Random orientation

Unidirectional

Preffered orientation

Bidirectional

Figure 1.3 Classification of composite materials [13]


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Particulate composites A composite whose reinforcement may be classified as particles is called a particulate composite. A particle, by definition, is non-fibrous and generally has no long dimension. Random orientation Random orientation: Orientation of particle is randomly distributed in all directions (ex: concrete). Preferred orientation Preferred orientation: Particle orientation is aligned to specific directions (ex: extruded plastics with reinforcement particles). Fiber reinforced composites Fibrous composites have fibers of reinforcing material(s) suspended in binding matrix. Unlike particles, a fiber has high length‐to diameter ratio, and further its diameter may be close to its crystal size. In general, materials tend to have much better thermo mechanical properties at small scale than at macro‐scale. Single layer These are actually made of several layers of fibers, all oriented in the same direction. Hence they are considered as “single‐layer” composites. These can be further categorized as: Continuous and long fibers: Examples include filament wound shells. Discontinuous and short‐fibers: Examples include fiber glass bodies of cars. Multi‐layer Here, reinforcement is provided, layer by layer in different directions. Laminate: Here, the constituent material in all layers is the same. Hybrid laminates: These have more than one constituent material in the composite structure.


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1.3 Summary of differences between steel and composites construction

Table 1.1 Differences between steel and composites construction [6] Property

Steel construction

Weight

High

Corrosion

conductivity

in structural weight Very durable in marine

resulting in high maintenance

environment, little

cost

maintenance

contribute to fire or generate toxic fumes

Thermal

Allows significant reduction

Rusts in marine environment

Non-combustible, will not Combustibility

Composite construction

High, must be insulated to prevent fire propagation and to control infrared signature

Electrical

High, inherently provides

conductivity

electromagnetic shielding

Combustible, surface must be protected in fire hazard areas

Low, inherent insulation more than sufficient

Low, must embed conductive layer if electromagnetic shielding is needed

As the reference of above table we can conclude that the various property like tensile strength, bending strength, stiffness strength, flexural test, corrosion resistance capacity, thermal conductivity, and electrical conductivity of composite material is better than the steel material. So from the reference of the above table we conclude that the composite material is most applicable and economic in Automobile, Aerospace and Marine engineering because of their good properties compare to steel. Now a day the use of composite material is more compare to steel or any other type of material.


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1.4 Use of Composites in Automobiles per Year

Table 1.2: Average Use of Composites in Automobiles per Year, 1988-1993 [15] Usage Applications

(kg x 106)

Bumper beam

42

Seat

14

Hood

13

Radiator

Matrix Material

Polyester (TS)

Polypropylene

Polycarbonate / PBT

Usage (kg x 106)

42

22

10

Manufacturing Process

SMC (comp. mould) GMT (comp. mould) Injection moulding Ext. blow

Usage (kg x 106)

40

20

13

4

Polyethylene

4

Roof panel

4

Epoxy

4

Other

11

Other

7

Other

8

Total

89

Total

89

Total

89

support

mould Filament wound

5

3

Above table give the value of composite material used in automobile application per year. As shown in above table the use of composite material is increase per year, because of their good mechanical property and weight saving capacity of material which is directly increase the load carrying capacity and fuel economy in Automobile, Aerospace and Marine engineering.


PAGE 7

1.5 Introduction of sandwich panel Sandwich structures (beams, panels etc.) consist of a combination of different materials that are placed together so that the material properties of each one can be utilized for the structural advantage of the whole assembly. Sandwich panels generally consist of three significant components, two thin, stiff face sheets and a thick, light and weaker core. The variety of types of sandwich constructions basically depends upon the configuration of the core, not to mention the material constituents. The most common types of core are: foam, honeycomb and web core truss. The faces that must be stiff, strong and thin; are separated and bonded to a light, weaker and thick core [9]. The adhesion of both materials is very important for the load transferring and therefore the functioning of the sandwich as a whole. Structural sandwich panels with cellular core are used in aircraft and automotive construction, in load bearing structures and in sports equipment, wherever weight-saving is required. The principal advantage of sandwich panels is that the rigidities can take any values in function of geometrical parameters. Thus, the designer has the choice for optimizing the material solution. Structural sandwich panel is a structure, which is realised by two skins separated by a lightweight core. Structural sandwich represents a good compromise between stiffness and lightness. Aluminium sandwich construction has been recognized as a promising concept for structural design of light weight systems such as wings of aircraft. A sandwich construction, which consists of two thin facing layers separated by a thick core, offers various advantages for design of weight critical structure. Depending on the specific mission requirements of the structures, aluminium alloys, high tensile steels, titanium or composites are used as the material of facings skins. Several core shapes and material may be utilized in the construction of sandwich among them; it has been known that the aluminium honeycomb core has excellent properties with regard to weight savings and fabrication costs.


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1.6 Structure of a sandwich panel Sandwich structured composites are a special class of composite materials which have become very popular due to high specific strength and bending stiffness. Low density of these materials makes them especially suitable for use in aeronautical, space and marine applications. Geometry of sandwich plate shown in figure 1.4.

Figure 1.4 Geometry of sandwich plate [4]

1.6.1 Definition sandwich composite Sandwich composites comprise of two thin but stiff face sheets attached on either side of a lightweight, thick slab known as core. Many variations of this definition are available but the key factor in making this type of materials remains the


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lightweight core, which reduces the overall density of the material and stiff skins providing strength. The structure of sandwich composites is shown in Figure 1.5. Concept of sandwich structured composite materials can be traced back to as early as the year 1849 AD but potential of this construction could be realized only during Second World War. Developments in aviation posed requirement of lightweight, high strength and highly damage tolerant materials. Sandwich structured composites, fulfilling these requirements became the first choice for many applications including structural components. Now their structural applications spread even to the ground transport and marine vessels. Integral bonding between skins and core prevents the interfacial failure under the applied load enhancing the flexural properties of sandwich composites. There is no general rule about the relationship between the thickness of skin and core. It depends on the application and required properties. Major advantage of sandwich structured composites is the possibility of tailoring properties by choosing appropriate constituting materials and their volume fractions.

Figure 1.5 Structure of a sandwich composite [14]


PAGE 10

1.7 Why sandwich panel used? Sandwich panels are used for design and construction of lightweight transportation systems such as satellites, aircraft, missiles, high speed trains. Structural weight saving is the major consideration and the sandwich construction is frequently used instead of increasing material thickness. The conventional single skin structure, which is of single plates reinforced with main frames and stiffeners normally necessitates a fair amount of welding, and has a considerable length of weld seams. Further, the lighter but thinner plates employed tend to increase weld distortions that may in some cases require more fabrication work to rectify. More weld seams also mean a greater number of fatigue initiation locations as well. Honeycomb sandwich construction, with a honeycomb core is sandwiched by two outer facing skins is better able to cope with such difficulties.

Face sheet

Honey comb Adhesive

Face sheet

Fabricated sandwich panel

Figure 1.6 Honeycomb sandwich panel [1]


PAGE 11

Sandwich panels also provide added structural weight savings in the structure. It is for these reasons that the sandwich construction has been widely adopted for large weight critical structures. Honeycomb-cored sandwich panels have been used as strength members of satellites or aircraft, thus efficiently reducing their structural weight.

1.8 Components in Sandwich Composites Sandwich composites primarily have two components namely, skin and core as shown in Figure 1.5. If an adhesive is used to bind skins with the core, the adhesive layer can also be considered as an additional component in the structure. The thickness of the adhesive layer is generally neglected because it is much smaller than the thickness of skins or the core. The properties of sandwich composites depend upon properties of the core and skins, their relative thickness and the bonding characteristics between them [5].

1.8.1 Core Based on the performance requirements, large numbers of materials are used as core. Popular core materials can be divided into three classes as described below: 1. Low density solid materials: open and closed cell structured foams, balsa and other types of wood. 2. Expanded high-density materials in cellular form: honeycomb, web core. 3. Expanded high-density materials in corrugated form: truss, corrugated sheets. High-density materials used for the purpose of making expanded core include aluminium, titanium and various polymers. The structure of the core material affects the interfacial contact area between skins and the core. Expanded high density materials normally provide much smaller contact area compared to the solid low density materials. The choice of appropriate structure for core provides


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additional parameter to design a sandwich composite as per given specifications or service conditions. The use of cores like closed cell structured foam gives some distinct advantages over open cell structured foams and cores. The specific compressive strength of close cell structured foams is much higher. They also absorb less moisture than open cell structured foam.

1.8.2 Skins A wide variety of materials are available for use as skins. Sheets of metals like aluminium, titanium and steel and fiber reinforced plastics are some of the common examples of skin materials. In case of fiber reinforced skins, the material properties can be controlled directionally in order to tailor the properties of the sandwich composite. Fiber reinforced polymers are used widely as skins due to their low density and high specific strength. Another advantage offered by the use of polymer composites in skins is that the same polymer can be used to make the skin and the core. Cross-linking of polymer between core and skin would provide adhesion strength level equal to the strength of the polymer. This provides possibility of making the skin an integral part of the structure eliminating the requirement of the adhesive. When an adhesive is used to bond the skin and the core together, selection of adhesives becomes very important, as they should be compatible with both the skin and the core materials. The adhesion must have desired strength level and should remain unaffected by the working environment[5]. In case of metallic components, welding or brazing is used as a means of binding the core and skins together. Use of adhesives is also possible but is limited to such cases where one or more of the components cannot withstand heat. Choice of skins is important from the point of view of the work environment as this part of the structure comes in direct contact with the environment. Corrosion, heat transfer characteristics, thermal expansion characteristics, moisture absorption and other properties of the whole sandwich composite can be


PAGE 13

controlled by proper choice of skin material. In most cases both skins of the sandwich are of the same type, but could be of different type depending upon specific requirements. Difference may be in terms of materials, thickness, fiber orientation, fiber volume fraction or in any other possible form.

1.8.3 Properties of Sandwich Composites Main advantage of any type of composite material is the possibility of tailoring their properties according to the application. The same advantage also applies to sandwich composites. Proper choice of core and skins makes sandwich composites adaptive to a large number of applications and environmental conditions. Some general characteristics of sandwich composites are described below [7] 1. Low density: choice of lightweight core or expanded structures of high-density materials decrease the overall density of the sandwich composite. Volume of core is considerably higher in the sandwich composite compared to the volume of skins so any decrease in the density of the core material has significant effect on the overall sandwich density. 2. Bending stiffness: this property comes from the skin part of the sandwich. Due to a higher specific stiffness sandwich composites result in lower lateral deformation, higher buckling resistance and higher natural frequencies compared to other structures. 3. Tensile and compressive strength: the z-direction properties are controlled by the properties of core and x and y directions properties are controlled by properties of skins. 4. Damage tolerance: use of flexible foam or crushable material as core makes sandwich material highly damage tolerant structure. For this reason foam core or corrugated core sandwich structured materials are popular materials in packaging applications.


PAGE 14

1.8.4 Advantages of sandwich panel  Large available choice of constituents for core and skins,  Low density leading to saving of weight,  High bending stiffness,  Higher damage tolerance,  Good vibration damping capacity.

Figure 1.7 Illustration of sandwich composite [16]

1.8.5 Limitations of Sandwich Composites There are current limitations that can be overcome through the development of new materials and manufacturing methods. Some of these are:  Higher thickness of the sandwich composites,  Higher cost of sandwich composites compared to conventional materials,  Processing is expensive,  Difficult to join,  Difficult to repair, if damaged.


PAGE 15

1.8.6 Applications of Sandwich Composites There are several applications that require materials of low density, high strength and high damage tolerance. Due to their lightweight, sandwich composites are widely used in various kinds of vehicles used for air, ground or sea transportation. Some of the main areas of applications of sandwich composites are listed below [6] 1. Structural applications: aircraft, spacecraft, submarine, ships and boats, surface transport vehicles, building materials etc, 2. Packaging materials, 3. Thermal and electrical insulation, 4. Storage tanks. Innovativeness is essential in finding new combinations of core and skin materials and new ways to use them in various applications where conventional materials have already reached their performance limits [9].

1.9 Work Objective In Automobile engineering, Aerospace, and Marine engineering load carrying capacity and fuel economy is necessary, this goal is achieve by using composite material and select the proper structure of composite material which decrease the weight of composite material without major change in material mechanical property like tensile strength, bending strength, flexural strength, and stiffness of the composite material. Now a day the use of composite material is increase at automobile side so it is very important to select the suitable structure of composite material which helps optimization of composite material.


PAGE 16

1.10 Outline of the Dissertation work Chapter-1: Introduction and information of composite material and sandwich panel composite material. Chapter-2: Study of standard review paper related to composite research work. Chapter-3: Introduction of honeycomb core and geometric parameter of unit cell of composite material. Chapter-4: Material selection for sandwich panel composite material which reduce weight without major change in mechanical property of composite material. Chapter-5: Perform experimental test like tensile test, bending test, and flexural test on sandwich panel composite material. Chapter-6: Compare result of test which performed on sandwich panel composite material. Chapter-7: Conclusion of the dissertation work. Chapter-8: Future scope of the dissertation work.


PAGE 17

CHAPTER-2 LITERATURE REVIEW

2.1 Introduction Automotive industry is on the verge of development. More and more comforts and safety are being incorporated in a vehicle. On other hand customers have stringent demand of fuel economy, high performance at low cost. In order to have high fuel economy the automotive manufacturers are induced to reduce weight. Several research papers have been studied. The weight reduction techniques so far in use are discussed in following section. With the recent emphasis on automobile weight reduction, all vehicle components are possible weight reduction targets. One group of components is exterior body panels. Significant weight reduction can be obtained through exterior body panels. There are several methods employed in automobile industry to reduce weight of a car body.

2.2 Work done G.A.O. Davies et al., “Compression after impact strength of composite sandwich panels.”

[1]

This paper deal with the two types of sandwich panels with carbon

epoxy skins and aluminium honeycomb core were subjected to low velocity impacts and then the damaged panels tested for their compression-after-impact (CAI) strength. One type of panel was found to be a very robust energy absorber, i.e. a thick-skin thin-core option. The other panels with their thin skins and thick core were found to penetrate easily whereupon the impact or forced the back-face to de-bond massively. These panels then had the worst CAI strength.


PAGE 18

Both the impact damage and the CAI behaviour to failure were simulated using a finite element model of skins and core. The model gave very respectable agreements with the impact tests even though the damage in skin and core were extremely complex mechanisms, involving progressive fibre fracture in the skin and elasto-plastic deformation in compression and shear in the honeycomb core. The model for CAI strength predicted well the failure load and the mode of propagation from the damaged zone. Vitaly Koissin, et al. “Compression strength of sandwich panels with sub-interface damage in the foam core” [2] This paper addresses the effect of a local quasi-static indentation or a low-velocity impact on the residual strength of foam core sandwich panels subjected to edgewise compression. The damage is characterized by a local zone of crushed core accompanied by a residual dent in the face sheet. Experimental studies show that such damage can significantly alter the compressive strength. Theoretical analysis of the face sheet local bending is performed for two typical damage modes (with or without a face–core debonding). The solutions allow estimation of the onset of (a) an unstable dent growth (local buckling) or (b) a compressive failure in the face sheet. The theoretical results are in agreement with the test data for two considered sandwich configurations. With the appearance of sandwich structures, the problem of their local bucking become entrenched in the design processes, due to a limited support provided by the core layer for the in-plane compressed face sheets. The local buckling (wrinkling) of intact sandwiches has been investigated in many studies, and a number of solutions were proposed. An experimental study is initially conducted to characterize the local damage and failure features and thus to provide an essential input for the theoretical modelling. Salih N. et al. “Effect of Core Material Stiffness on Sandwich Panel Behaviour. Beyond the Yield Limit”

[3]

Research efforts are continuously looking for new,

better and efficient construction materials. The main goal of these researches is to improve the structural efficiency, performance and durability. New materials


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typically bring new challenges to designer who utilizes these new materials. In the past decades various sandwich panels have been implemented in aerospace, marine, architectural and transportation industry. Light-weight, excellent corrosion characteristics and rapid installation capabilities has created tremendous opportunities for these sandwich panels in industry. Sandwich panel normally consists of a low-density core material sandwiched between two high modulus face skins to produce a lightweight panel with exceptional stiffness. The face skins act like the flanges of an I-beam to provide resistance to the separating face skins and carrying the shear forces. The faces are typically bonded to the core to achieve the composite action and to transfer the forces between the components. The model has been validated against numerical and experimental cases that are available in the literature. In addition, experimental investigation has been carried out to validate the finite element model and to verify some selected cases. The finite element model shows very good agreement with the previous work and the experimental investigation. It is proved in this study that the load carrying capacity of the panel increases as the core material goes beyond the yield point. Load transmitted to the face sheets gets higher as the core stiffness gets softer. The stiffer the core material is, the closer the sandwich panel behaviour gets to isotopic plate, i.e., face sheets are going to yield before core material. P. Noury, et al, “Lightweight construction for advanced shipbuilding – recent development”

[4]

. In this paper some recent advances in lightweight construction

for modern shipbuilding are presented. The paper first introduces conventional and more advanced types of lightweight structures used in the ship building industry. Following a description of lightweight structures and their current use in shipbuilding, emphasis is put on naval applications of composites, and in particular on aspects related to cost benefit assessment and survivability. The following part reports on the use of adhesive bonding for superstructures of highspeed craft and passenger ships. It focuses on material selection, design and analysis, manufacture and application. In this paper a review of some of the recent progress in lightweight construction for advanced shipbuilding has been presented. The motivations for using


Page 20

conventional and more advanced types of lightweight materials and structures have been reviewed; commonly lightweight structures are used to increase payload, to reach higher speeds and to lower fuel consumption. In naval applications composite materials have been chosen because of the added benefit offered by attractive properties for specific applications. However, the wise use of composites requires an understanding of the differences between steel and composites structures. The specific detailed design requirements of a composite structure differ from those of a corresponding steel structure. Based on this principle, a cost benefit assessment method has been developed to compare steel and composite designs in order to make a rational selection and establish a balanced composite design. In addition a review of survivability of naval composites structures together with focus on design improvements, with particular reference to novel joint designs, also been presented. Ji-Hyun Lim, “Ki-Ju Kang, Mechanical behavior of sandwich panels with tetrahedral and Kagome truss cores fabricated from wires”

[5]

Wires are great

candidates as the raw material for truss periodic cellular metals because they can display high strength as in piano wires, are easy to fabricate, and can be controlled to be defect free. New approaches based on tri-axial weaving of wires to create ideal trusses, i.e., tetrahedral and Kagome truss have been presented. The mechanical properties of the sandwich panels with the truss cores fabricated by using the new approaches under compression and bending loadings are analyzed by elementary beam theory and experiments. The relative density, stiffness, and strength of the sandwich panels are estimated by the derived equations and compared with the measured results. The failure mechanisms of the sandwich panels are analyzed, and also benefits and shortcomings of each approach with respect to mechanical performance and production are discussed. F. Meraghni, F. Desrumaux, M.L. Benzeggagh, “Mechanical behaviour of cellular core for structural sandwich panels”

[6]

. This paper deals with the analysis of the

mechanical properties of the core materials for sandwich panels. In this work, the core is firstly a honeycomb and secondly tubular structure. These kind of core


Page 21

materials are extensively used, notably in automotive construction (structural components, load floors...). For this study, three approaches are developed: a finite element analysis, an analytical study and experimental tests. Structural members made up of two stiffs, strong skins separated by a lightweight core (foam, honeycomb, tube...) are known as sandwich panels. The separation of the skins by the core increases the inertia of the sandwich panel, the flexure and shear stiffness. This increase is obtained with a little increase in weight, producing an efficient structure to resist bending and buckling loads. A new analytical method to analyse sandwich panels core will be presented. These approaches (theoretical and experimental) are used to determine elastic properties and ultimate stress. A parameter study is carried out to determine elastic properties as a function of geometrical and mechanical characteristics of basic material. Both theoretical and experimental results are discussed and a good correlation between them is obtained. B. Castanie, C. Bouvet, et al. “Modelling of low-energy/low-velocity impact on Nomex honeycomb sandwich structures with metallic skins”

[7]

. In the aircraft

industry, manufacturers have to decide quickly whether an impacted sandwich needs repairing or not. Certain computation tools exist at present but they are very time-consuming and they also fail to perfectly model the physical phenomena involved in an impact. In a previous publication, the authors demonstrated the possibility of representing the Nomex honeycomb core by a grid of nonlinear springs and have pointed out both the structural behaviour of the honeycomb and the influence of core-skin boundary conditions. This discrete approach accurately predicts the static indentation on honeycomb core alone and the indentation on sandwich structure with metal skins supported on rigid flat support. In this study, the domain of validity of this approach is investigated. It is found that the approach is not valid for sharp projectiles on thin skins. In any case, the spring elements used to model the honeycomb cannot take into account the transverse shear that occurs in the core during the bending of a sandwich. To overcome this strong limitation, a multi-level approach is proposed in the present article. In this approach, the sandwich structure is modelled by Midline plate elements and the


Page 22

computed static contact law is implemented in a nonlinear spring located between the impact or and the structure. Thus, it is possible to predict the dynamic structural response in the case of low-velocity/low-energy impact on metalskinned sandwich structures. A good correlation with dynamic experimental tests is achieved. M. Meo, A.J. Morris.” Numerical simulations of low velocity impact on an aircraft sandwich panel” [8].This paper describes the results from experimental and numerical simulation studies on the impact and penetration damage of a sandwich panel by a solid, round-shaped impact. The main aim was to prove that a correct mathematical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design an impact-resistant aircraft structure. Part of this work presented is focused on the recent progress on the materials modelling and numerical simulation of low-velocity impact response onto a composite aircraft sandwich panel. It is based on the application of explicit finite element (FE) analysis codes to study aircraft sandwich structures behaviour under low-velocity impact conditions. Good agreement was obtained between numerical and experimental result, in particular, the numerical simulation was able to predict impact damage and impact energy absorbed by the structure. B. Lascoup, et al. “On the mechanical effect of stitch addition in sandwich panel” [9]

. Monolithic stitched composite materials successfully inspired the addition of

transverse reinforcements in the case of sandwich structures. Indeed, the gains are undeniable in term of ultimate stress and of modulus regarding the principal mechanical tests practiced on sandwich (bending, shearing and compression). These bonds reduce the impact of the inter-laminar shearing which tends to break the connection between the core and the skins. Moreover, such reinforcements finally increase mechanical properties in the thickness direction, thus solving the principal disadvantage of these sandwich structures. Although the mass of such stitched panels is higher than that of the unstitched ones, the specific performances remain considerable. The direct influence of the macro-structural


Page 23

parameters of the stitches (step and angle) on the mechanical behavior of the structure is presented. It was also clearly highlighted that it is necessary to find a compromise between the structural parameters and the mass in order to obtain the expected mechanical performances. M. Meo, “The response of honeycomb sandwich panels under low-velocity impact loading” [10]. This paper describes the results of an experimental investigation and a numerical simulation on the impact damage on a range of sandwich panels. The test panels are representative of the composite sandwich structure of the engine nacelle Fan Cowl Doors of a large commercial aircraft. The low-velocity impact response of the composites sandwich panels is studied at five energy levels, ranging from 5 to 20 J, with the intention of investigating damage initiation, damage propagation, and failure mechanisms. These impact energy levels are typically causing barely visible impact damage (BVID) in the impacted composite face sheet. A numerical simulation was performed using LS-DYNA3D transient dynamic finite element analysis code for calculating contact forces during impact along with a failure analysis for predicting the threshold of impact damage and initiation of de-laminations. Good agreement was obtained between numerical and experimental results. In particular, the numerical simulation was able to predict the extent of impact damage and impact energy absorbed by the structure. The results of this study is proving that a correct numerical model can yield significant information for the designer to understand the mechanism involved in the lowvelocity impact event, prior to conducting tests, and therefore to design a more efficient impact resistant aircraft structure. Jeom Kee Paik, “The strength characteristics of aluminium honeycomb sandwich panels”

[11]

. Aluminium sandwich construction has been recognized as a

promising concept for structural design of lightweight transportation systems such as aircraft, high-speed trains and fast ships. The aim of the present study is to investigate the strength characteristics of aluminium sandwich panels with aluminium honeycomb core theoretically and experimentally. A series of strength


Page 24

tests are carried out on aluminium honeycomb-cored sandwich panel specimen in three point bending, axial compression and lateral crushing loads. Simplified theories are applied to analyze bending deformation, buckling/ultimate strength and crushing strength of honeycomb sandwich panels subject to the corresponding load component. The structural failure characteristics of aluminium sandwich panels are discussed.


Page 25

CHAPTER-3 HONEYCOMB CORE SANDWICH PANEL

3.1 Introduction of honeycomb core For design and construction of lightweight transportation systems such as satellites, aircraft, high-speed trains and fast ferries, structural weight saving is one of the major considerations. To meet this requirement, sandwich construction is frequently used instead of increasing material thickness. This type of construction consists of thin two facing layers separated by a core material. Potential materials for sandwich facings are aluminium alloys, high tensile steels, titanium and composites depending on the specific mission requirement. Several types of core shapes and core material have been applied to the construction of sandwich structures. Among them, the honeycomb core that consists of very thin foils in the form of hexagonal cells perpendicular to the facings is the most popular [1]. A sandwich construction provides excellent structural efficiency, i.e., with high ratio of strength to weight. Other advantages offered by sandwich construction are elimination of welding, superior insulating qualities and design versatility. Even if the concept of sandwich construction is not very new, it has primarily been adopted for non-strength part of structures in the last decade. This is because there are a variety of problem areas to be overcome when the sandwich construction is applied to design of dynamically loaded structures. To enhance the attractiveness of sandwich construction, it is thus essential to better understand the local strength characteristics of individual sandwich panel/beam members.


Page 26

3.2 Honeycomb structure

Figure 3.1 Honeycomb core [16]

Figure 3.2 Unit cell for honeycomb core [8]


Page 27

3.2.1 Definition of the unit cell This unit cell is a hexagonal cell. In fact, with a hexagonal cell, it’s possible to describe the entire honeycomb core. The periodicity of the structure is used here. In the second time, the unit cell is built up with one quarter of one central wall and one quarter of one inclined wall. This reduction in the size of the cell to be studied is because of the different symmetries [8]. The area shown in Fig. 3.3, describes the unit cell and its parameters.

Figure 3.3 Reduced unit cell and its parameters [8]

Figure 3.4 Geometrical parameters for honeycomb core [8]


Page 28

Figure 3.5 Unit cell of polyethylene sheet

Figure 3.5 show the construction of unit cell of polyethylene sheet. As shown in figure the vertical wall thickness of hexagon is 10mm, and thickness of inclined face is 5mm, angle between two walls is 60о, length of inclined wall and vertical is 20mm, and total height of the hexagon cell is 40mm,and thickness of the polyethylene sheet is 4mm. Above geometric dimension of unit cell of polyethylene sheet is fix from standard reference paper and consider maximum weight reduction of material without major change in material mechanical property. Hexagon structure of the core material is select instead of triangle and square shape because in hexagon shape we get higher weight reduction, and load distribution is higher compare to triangle and square shape of inner core material. Dimension of geometry parameter a = 20 mm, e = 10 mm,


Page 29

θ = 30о, H = 40 mm, = 5 mm As per previous research work hexagonal structure of inner core material for sandwich panel composite selected. Geometric parameter of hexagonal structure is fixed discussed as above.


Page 30

CHAPTER-4 MATERIAL SELECTION FOR SANDWICH PANEL

4.1 Characteristics of materials for sandwich panel Various characteristics of sandwich panel are discussed below, in sandwich panel face material and core material is used its characteristics are discussed below [12].

4.1.1 Face materials and its property If the sandwich is supported on both sides, and then stressed by means of a force in the middle of the beam, then the bending moment will introduce shear forces in the material. The shear forces results in the bottom skin being in tension and the top skin being in compression. The core material spaces these two skins apart. The thicker the core material, the stronger the composite. This principle works in much the same way as an I-beam does. A. Metal (1) Aluminium (2) Steel (3) Stainless Steel B. Composites (1) Fiberglass (2) High Pressure Laminates Plastic Sheet (ABS, Polypropylene, etc.) C. Wood (1) Plywood (2) Hardboard (3) Prefinished Veneer


Page 31

Aluminium composite Panel Aluminium is a very versatile metal, touches every aspect of our lives, from aircrafts to Automobiles, from power cables to foils, aluminium can be fashioned into myriad shapes in a variety of applications and lately the building industry has caught the fancy of the versatility and Performance of the material.

Table 4.1: Materials property of aluminium and steel [15] Properties/materials

Aluminium

Steel

Stiffness N/m

22.9 x 103

22.65 x 103

Density kg/m3

2700

7800

Weight

Low

high

70000 x 106

210000 x 106

Shear modulus N/m2

27000 x 106

81000 x 106

Poisson ratio

0.33

0.3

23 x 10-3

12 x 10-3

Corrosion resistance

High

Low

Ductility

High

Low

Recyclability

Very good

Good

Cost

High

Low

Young modulus of elasticity 2

N/m

Co-efficient of thermal expansion 1/K

Aluminium products are more commonly used in the construction of Buildings as composite panels in wall claddings, curtain walling, and roofing. Aluminium is an energy intensive material.


Page 32

Figure 4.1 Aluminium plate

Figure 4.1 shows aluminium plates is considered for face sheet material. Size of face sheet is length is 84mm, width is 1mm, and height is 133.5mm for tensile test and for bending test the size of aluminium sheet is length is 225mm, width is 105mm and height is 1mm, and for flexural test size of aluminium sheet is length is 225mm, height is 105mm, and width is 1mm. Table 4.1 shows the material property of aluminium is very high compare to steel and also weight is less compare to steel, so aluminium material is most suitable for sheet metal. So in my test model aluminium is considered for sheet metal.


Page 33

Corrosion resistance property is very high of aluminium material which is most important for automobile and aerospace application.

4.1.2 Core materials and its property Core materials form the basis for sandwich composite structures, which clearly have advantages in marine construction. A core is any material that can physically separate strong, laminated skins and transmit shearing forces across the sandwich. Core materials range from natural species, such as balsa and plywood, to highly engineered honeycomb or foam structures. The dynamic behaviour of a composite structure is integrally related to the characteristics of the core material used [16]. A. Honeycomb Materials (1) Kraft Honeycomb (2) Aluminium Honeycomb (3) Fluted Polypropylene Aramid Paper Honeycomb

B. Foam (1) Polystyrene Foam (2) PVC Foam (3) High Density Urethane Foam (4) Polyethylene (5) Polyurethane

C. Wood and Other Material (1) Plywood (2) End Grain Balsa (3) Fluted Polypropylene

In my dissertation work aluminium honey comb material is used for face sheet and polyethylene material is used for core material, because of their good mechanical and weight saving property of material.


Page 34

Table 4.2: Materials property of polyethylene core [15] Mechanical Property

General Units

purpose polystyrene

MN/m2

34.5-48.3

%

20-30

Modulus in tension

MN/m2

2000-3000

Impact strength

J/m

37-59

MN/m2

48.3-75.8

in

0.15-0.35

Tensile strength Elongation at Break

Flexural Strength Deflection Hardness

Rockwell scale

M45-M60

Polyethylene Sheet CD case made from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) Disposable polystyrene razor. Polystyrene (PS) is economical, and is used for producing plastic model assembly kits, CD, "jewel" cases, license plate frames, and many other objects where a fairly rigid, economical plastic is desired. Production methods include thermoforming and injection moulding. Polyethylene sheets are good thermal insulators and are therefore often used as building insulation materials, such as in structural insulated panel building systems. They are also used for non-weight-bearing architectural structures (such as ornamental pillars). PS foams exhibit also good damping properties, therefore it is used widely in packaging.


Page 35

Figure 4.2 Polyethylene sheet without hexagon

Two type of polyethylene shape is considered without hexagonal structure shown in figure 4.2. Polyethylene material is considered for core material or inner material. Size of polyethylene sheet is length is 84mm, width is 4mm, and height is 133.5 mm for tensile test and for bending test the size of material: length is 225mm, width is 105mm and height is 4m, and for flexural test the size of material is length is 225mm, width is 4mm and height is 105mm.


Page 36

Figure 4.3 Polyethylene sheet with hexagonal structure

With hexagonal structure shown in figure 4.3. Size of polyethylene sheet is length is 84mm, width is 4mm, and height is 133.5 mm for tensile test and for bending test the size of material: length is 225mm, width is 105mm and height is 4mm, and for flexural test the size of material is length is 225mm, width is 4mm and height is 105mm.


Page 37

4.1.3 Binder materials and its property The choice of a resin system for use in any component depends on a number of its characteristics, with the following probably being the most important for most com- posited structures [9]. Types of resin use in sandwich panel A. Thermoplastic B. Thermoset (1) Epoxy resins (2) Vinyl ester resins (3) PE (Polyester) (4) PVDF (poly vinyl die florid) (5) NANO PVDF Properties of resin It must be understood that the adhesive properties of a resin system is important in achieving the full mechanical properties of a composite. The adhesion of the resin matrix to the fiber reinforcement or to a core material in a sandwich construction is important. Mechanical properties Two important mechanical properties of any resin system are its tensile strength and stiffness. After a cure period of seven days at room temperature it can be seen that a typical epoxy will have higher properties than a typical polyester and vinyl ester for both strength and stiffness. The beneficial effect of a post cure at 80C for five hours can also be seen. Micro-Cracking The strength of a laminate is usually thought of in terms of how much load it can withstand before it suffers complete failure. This ultimate or breaking strength is the point at which the resin exhibits catastrophic breakdown and the fiber-


Page 38

reinforcements break. Here the well-known adhesive properties of epoxy help laminates achieve higher micro cracking strains. Resin toughness can be hard to measure, but is broadly indicated by its ultimate strain to failure. Generally composites show excellent fatigue resistance when compared with most metals. Epoxy based laminates tend to show very good fatigue resistance when compared with both polyester and vinyl ester, this being one of the main reasons for their use in aircraft structures. Degradation from water ingress An important property of any resin, particularly in a marine environment, is its ability to withstand degradation from water ingress. All resins will absorb some moisture, adding to a laminate's weight, but what is more significant is how the absorbed water affects the resin and resin/fiber bond in a laminate, leading to a gradual and long term loss in mechanical properties. A thin polyester laminate can be expected to retain only 65% of its inter-laminar shear strength after immersion in water for a period of one year, whereas an epoxy laminate immersed for the same period will retain around 90%.


Page 39

CHAPTER-5 EXPERIMENTAL SET-UP AND TEST MODEL OF COMPOSITE MATERIAL

5.1 Experimental set-up In test model of composite material aluminium and polyethylene material is used. Sandwich panel structure is used for composite material. Aluminium plate is used as cover plate or skin plate and polyethylene plate is used as an inner material or core material.

Test piece

Figure 5.1 Experimental set-up of Flexural test


Page 40

Tensile test set-up

Bending test set-up

Figure 5.2 Experimental set-ups for tensile and bending test


Page 41

As shown in figure 5.1 flexural limits is check on compression testing machine, and tensile limit of composite material and bending limit of composite material is checked and measured on universal testing machine (UTM) shown in figure 5.2.

Figure 5.3 Universal testing machine

Figure 5.3 shows set–up of universal testing machine at R.K.UNIVERSITYRAJKOT. Control of UTM machine is computerised and on UTM tensile test and bending test both test perform. Shape and size of material is entering by using computer, and then test is performed.


Page 42

HL-590 model series except for the automatic pace setting arrangement. In these series of machines the pace setting is achieved through a combination of advanced electronic and hydraulic system. Pacing speed is programmed through the key board which is directly displayed in engineering units on the digital indicator. When the machine is given the command to start it immediately controls the signal passed on to the proportional valve. Maximum capacity of UTM is 400 KN.

5.2 Tensile test of composite material Tensile test of composite material was performed on universal testing machine (UTM) at R.K.UNIVERSITY-RAJKOT. For tensile test upper jaw and lower jaw have rectangle shape and inner side of jaws grip is provided for holding test piece. Two type of shape consider for tensile test, without hexagonal construction of inner core material simple or solid polyethylene sheet or plate is used, and with hexagonal construction hexagonal shape of polyethylene composite plate were used. Table 5.1 Sample size and mass for tensile test Material

Structure

Size

Weight

Polyethylene

Simple

Length=84mm

135.6gm

Height=133.5mm Width=6mm Polyethylene

Hexagon

Length=84mm

82.4gm

Height=133.5mm Width=6mm

Size of composite material is same for both without hexagonal composite material and with hexagonal composite material shown in table 5.1, and the structure of inner core material is different like without hexagon shape. In hexagonal composite material we get 39.23% reduction of weight due to this reduction of


Page 43

weight the load carrying capacity can be increased in automobile, aerospace and marine engineering, with negligible reduction in tensile stress subjected material.

Aluminium Polyethylene

Figure 5.4 Composite material without hexagon

Aluminium

Polyethylene

Figure 5.5 Composite material with hexagon


Page 44

Figure 5.4 shows composite material used for tensile test is without hexagonal structure and figure 5.5 shows composite materials used for tensile test is with hexagonal structure. The size of both test samples is same but in hexagon structure we get more weight reduction which is very help-full in auto-mobile and aero-space application. And stress and load distribution is better in hexagonal type shape and also weight reduction is higher compare to square and triangle type structure of core material.

Upper jaw Test piece Bottom jaw

Figure 5.6 Experimental set-up of tensile test


Page 45

Test procedure Figure 5.6 shows tensile set-up fix the test piece of composite in between jaws of the universal testing machine and then tight both upper jaw and bottom jaw. Then after set the shape of the test piece in universal testing machine software by use of computer and then input the dimension of rectangle shape of composite test piece, after input the dimension start applying load at both end at opposite direction as shown in figure 5.6. Tensile stress capacity, all results and graph is generated in UTM.

5.3 Bending test of composite material Bending test of composite material was performed on universal testing machine (UTM) at R.K.UNIVERSITY-RAJKOT. For bending test upper jaw have rectangle shape and test piece is arranged on lower jaw as shown in figure. Two type of shape consider for bending test, without hexagonal construction of inner core material simple or solid polyethylene sheet or plate is used, and with hexagonal construction hexagonal shape of polyethylene composite plate were used.

Table 5.2 Sample size and mass for bending test Material

Structure

Size

Weight

Polyethylene

Simple

Length=225mm

133.6gm

Height=6mm Width=105mm Polyethylene

Hexagon

Length=225mm

81.4gm

Height=6mm Width=105mm


Page 46

Figure 5.7 Preparation of experimental set-up of bending test

Size of composite material is same shown in table 5.2, and the structure of inner core material is different like without hexagon shape. In hexagonal composite material we get 39.08% reduction of weight due to this reduction of weight the load carrying capacity can be increased in automobile, aerospace and marine engineering, with negligible reduction in bending stress subjected material. Preparation of experimental set-up of bending test is shown figure 5.7.


Page 47

Movable jaw

Test piece

Fix jaw

Figure 5.8 Experimental set-up of bending test

Test procedure Figure 5.8 shows bending test of composite material, composite test piece is resting on fix jaw, the distance between two jaw is fix it is kept 120mm, upper jaw is movable and its setup is prepared as shown in figure5.8, load is applied by upper jaw, and bending stress capacity and all result and graph is generated in universal testing machine. Shape and size of test piece is manually enter in universal testing machine software and then after bending test is performed.


Page 48

Figure 5.9 Test piece after bending test

After perform bending test on sandwich panel composite material, material try to come its original position without break, so composite material elastic property is also improve, figure 5.9 show the composite material after bending test.


Page 49

CHAPTER-6 RESULTS AND DISCUSSION

6.1 Tensile test of composite material Tensile test of composite material is performed on universal testing machine at R.K. UNIVERSITY-RAJKOT. There are two types of sandwich panel composite material is consider for tensile test sandwich panel composite material without hexagonal structure sandwich panel composite material with hexagonal structure of core material. Tensile test of composite material without hexagon structure

Figure 6.1 Tensile result generated by UTM (composite material without hexagon)


Page 50

As shown in figure 6.1 the maximum loads apply on composite material is 13.54 KN, without hexagon structure. And at peak load the displacement is 6.19 mm. Peak load and displacement is highlight in result table of tensile of composite material without hexagon. Shape Unit

:

[1 mm sq.mm ]

Sample Length: [84 mm

]

Sample Breadth: [06 mm

]

Sample Height: [133.5 mm

]

No of Readings: [95

]

SR NO.

LOAD (KN)

DISPLACEMENT (mm)

0000000

00008.06

00000.81

0000001

00009.32

00001.10

0000002

00010.00

00001.37

0000003

00010.69

00001.67

0000004

00011.20

00001.94

0000005

00011.44

00002.23

0000006

00011.75

00002.55

0000007

00011.78

00003.11

0000008

00011.93

00003.43

0000009

00012.11

00003.75

0000010

00012.32

00004.04

0000011

00012.64

00004.36


Page 51

0000012

00012.98

00004.65

0000013

00013.20

00004.97

0000014

00013.35

00005.55

0000015

00013.46

00005.87

0000016

00013.54

00006.19

Tensile test of composite material with hexagonal structure

Figure 6.2 Tensile result generated by UTM (composite material with hexagon)


Page 52

Result of tensile test with hexagon structure is shown on figure 6.2. Figure shows composite material with hexagon structure is break at 12.21 KN, and displacement at maximum load is 4.54 mm. Peak load and displacement is highlight in result table of tensile of composite material with hexagon. Shape Unit

:

[1 mm sq.mm ]


]


]

Sample Height: [133.5 mm

]

No of Readings: [83

]

SR NO.

LOAD (KN) DISPLACEMENT (mm)

0000389

00007.39

00000.54

0000390

00008.37

00000.81

0000391

00009.07

00001.10

0000392

00009.65

00001.37

0000393

00010.49

00001.94

0000394

00010.82

00002.23

0000395

00011.06

00002.50

0000396

00011.43

00002.80

0000397

00011.67

00003.09

0000398

00011.85

00003.39

0000399

00011.98

00003.68

0000400

00012.05

00004.24


Page 53

0000401

00012.21

00004.54

Comparison of tensile test with hexagon and without hexagon structure 7

6

Displacement (mm)

5

4

WITH HEXAGON

3

WITHOUT HEXAGON

2

1

13.54

13.46

13.35

13.2

12.98

12.64

12.21

12.11

11.93

11.78

11.75

11.2

11.44

10.69

0

Load (KN)

Figure 6.3 Comparison of tensile test result

Figure 6.3 shows displacement verses load graph is shown for both without hexagonal type sandwich composite material and with hexagon type sandwich composite material, as shown in figure peak load 13.54 KN indicate the tensile test result of sandwich panel composite material without hexagonal structure, and 12.21 KN indicate the tensile result of sandwich panel composite material with hexagonal.


Page 54

6.2 Bending test of composite material Bending test of composite material is performed on universal testing machine at R.K. UNIVERSITY-RAJKOT. There are two types of sandwich panel composite material is consider for bending test sandwich panel composite material without hexagonal structure and sandwich panel composite material with hexagonal structure of core material. Bending test of composite material without hexagon structure

Figure 6.4 Bending result generated by UTM (composite material without hexagon)


Page 55

Figure 6.4 shows without hexagonal structure composite material maximum load sustain 14.47 KN. And at peak load displacement is 60.45 mm. Peak load and displacement is highlight in result table of bending of composite material without hexagon. Shape Unit

:

[1 mm sq.mm ]


]


]

Sample Height: [06 mm

]

No of Readings: [67

]

SR NO


0000088

00014.28

00052.59

0000089

00014.32

00053.08

0000090

00014.27

00053.56

0000091

00014.25

00054.05

0000092

00014.34

00054.55

0000093

00014.19

00055.05

0000094

00014.16

00056.02

0000095

00014.44

00056.50

0000096

00014.36

00056.99

0000097

00014.45

00057.49

0000098

00014.44

00057.99

0000099

00014.42

00058.48


Page 56

0000100

00014.38

00058.98

0000101

00014.40

00059.95

0000102

00014.47

00060.45

Bending test of composite material with hexagon structure

Figure 6.5 Bending result generated by UTM (composite material with hexagon)

Figure 6.5 shows with hexagonal structure composite material maximum load sustain 13.92 KN. And at peak load displacement is 48.16 mm. Peak load and


Page 57

displacement is highlight in result table of bending of composite material with hexagon. Shape Unit

:

[1 mm sq.mm ]


]


]

Sample Height: [06 mm

]

No of Readings: [116

]

SR NO.


0000051

00005.43

00000.00

0000052

00009.60

00003.88

0000053

00011.67

00004.92

0000054

00012.67

00005.44

0000055

00013.28

00005.96

0000056

00013.51

00006.50

0000057

00013.58

00007.05

0000058

00013.55

00007.59

0000059

00013.61

00008.13

0000060

00013.70

00008.67

0000061

00013.82

00009.74

0000062

00013.70

00010.28

0000063

00013.78

00010.80

0000064

00013.77

00011.34

0000065

00013.63

00011.88


Page 58

0000066

00013.55

00012.43

0000067

00013.70

00012.97

0000068

00013.73

00014.05

0000069

00013.66

00014.62

0000070

00013.76

00015.16

0000071

00013.61

00015.72

0000072

00013.54

00016.27

0000073

00013.66

00016.81

0000074

00013.81

00017.37

0000075

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0000076

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0000077

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00020.09

0000079

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00020.63

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00021.17

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00021.74

0000082

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00022.80

0000083

00013.73

00023.36

0000084

00013.70

00023.91

0000085

00013.68

00024.47

0000086

00013.63

00025.01

0000087

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00025.60

0000088

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00026.14


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0000089

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00027.23

0000090

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00027.79

0000091

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00028.36

0000092

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0000093

00013.55

00029.47

0000094

00013.76

00030.01

0000095

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00030.57

0000096

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00031.66

Comparison of bending test with hexagon and without hexagon structure 70

60

Displacement (mm)

50

40 WITHOUT HEXAGON

30

WITH HEXAGON 20

10

0

Load (KN)

Figure 6.6 Comparison of bending test result


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Figure 6.6 shows displacement verses load graph is shown for both without hexagonal type sandwich composite material and with hexagon type sandwich composite material, as shown in figure 14.47 KN indicate the bending test result of sandwich panel composite material without hexagonal structure, and 13.92 KN indicate the bending result of sandwich panel composite material with hexagonal

6.3 Flexural test of composite material Figure 6.7 shows Flexural test of composite material. Sandwich panel composite material is bend at 100о by applying the compression load, and then after removing the load sandwich panel composite material come its original shape without break or any major defect in sandwich panel composite material. So elastic limit of sandwich panel composite material is good which is necessary in automobile, aerospace and marine application.

Upper jaw

Test piece

Bottom jaw

Figure 6.7 Flexural test of composite material


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Test procedure In flexural test composite material is placed vertically in between two jaws, upper jaw is movable in vertical position while bottom jaw is fixed, so load is gradually apply by upper jaw and due to this force composite material is bend, and after release force composite material come its original shape without change in dimension and any major defect in sandwich panel composite material. As shown in figure 6.7 material is bend at 100о, and after removing force material come its original shape, so elastic limit of composite material is good, some time composite material is also used in civil construction because of its good elastic limit of composite material.


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CHAPTER-7 CONCLUSION

Bending test, Tensile test, and Flexural test is performed on sandwich panel composite material. Two type of inner core structure is consider for sandwich panel composite material, without hexagonal composite material, and with hexagonal composite material. And it is observed that with hexagonal composite material weight saving is 39% compared with without hexagonal composite material. From tensile test and bending test of composite material, tensile strength and bending strength capacity of with hexagonal composite material is less compare to without hexagonal composite material, but it can be negligible. Hence sandwich panel composite material (with hexagonal structure) is acceptable in Automobile, Aerospace, and Marine engineering.


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CHAPTER-8 FUTURE RECOMMENDATION

By using various composite materials provide to designer the freedom to choose the materials, laminates and manufacturing method to suit the design requirement. Bending test, Tensile test, and Flexural test can also be extended to another type of composite materials and structure of the composite materials. Bending test, Tensile test is done on hexagonal honeycomb cored panels and there will be scope for study on square honeycomb cored panel, and finite element analysis (FEA), and optimization using Engineering Optimization Algorithm is scope for sandwich panel composite materials.


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BIBIOGRAPHY AND REFERENCES

[1]

K.Kantha Rao, K. Jayathirtha Rao, A.G.Sarwade, B.Madhava Varma,

Bending Behavior of Aluminum Honey Comb Sandwich Panels, International Journal of Engineering and Advanced Technology (IJEAT), ISSN: 2249 – 8958, (2002). [2] G.A.O. Davies, D. Hitchings, T. Besant, A. Clarke, C. Morgan, Compression after impact strength of composite sandwich panels, Composites Science and Technology 69 (2009), pp 2231–2240. [3] Vitaly Koissin, Andrey Shipsha, Vitaly Skvortsov, Compression strength of sandwich panels with sub-interface damage in the foam core, Composites Science and Technology 69 (2009), pp 2231–2240. [4] Salih N. Akour, Hussein Z. Maaitah, Effect of Core Material Stiffness on Sandwich Panel Behavior Beyond the Yield Limit, Proceedings of the World Congress on Engineering (2010). [5] X. Frank Xu, Pizhong Qiao, Homogenized elastic properties of honeycomb sandwich with skin effect, International Journal of Solids and Structures 39 (2002), pp 2153–2188. [6] Kujala, P., Metsä, A. and Nallikari, M, All steel sandwich panels for ship applications, Helsinki University of Technology, (2000). [7] Ji-Hyun Lim, Ki-Ju Kang, Mechanical behavior of sandwich panels with tetrahedral and Kagome truss cores fabricated from wires, International Journal of Solids and Structures 43 (2006), pp 5228–5246.


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[8] F. Meraghni, F. Desrumaux, M.L. Benzeggagh, Mechanical behaviour of cellular core for structural sandwich panels, Composites: Part A 30 (1999), pp 767–779. [9] Bhagwan D. Agarwal, Lawrence J. Broutman, K. Chandrashekhara, Analysis and performance of fiber composites, ISBN: 978-81-265-3636-8, (2006). [10] M D Banea, L F M da Silva, Proceedings of the Institution of Mechanical Engineers, Journal of Materials Design and Applications, (2009). [11] M. Meo, R. Vignjevic, G. Marengo, The response of honeycomb sandwich panels under low-velocity impact loading, International Journal of Mechanical Sciences 47 (2005). [12] Jeom Kee Paik, Anil K. Thayamballi, Gyu Sung Kim, The strength characteristics of aluminium honeycomb sandwich panels, Thin-Walled Structures 35 (1999). [13] Robert m. Jones, Mechanics of composite materials, ISBN: 1-56032-712-X, (2003). [14] Wennberg, David, Light-Weighting Methodology in Rail Vehicle Design through Introduction of Load Carrying Sandwich Panels, Design Department of Aeronautical and Vehicle Engineering, (April 2011). [15] Mazumdar, Sanjay K, Composite manufacturing Materials, Product, and Process Engineering, CRC PRESS Boca Raton London New York Washington, (2002). [16] Nikhil Gupta, Characterization of syntactic foams and their sandwich composites Modeling and experimental approaches, Indian Institute of Science, Bangalore, India, (August-2003).


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APPENDIX

I.

A research paper entitled “Analysis Of Composite Material

(Sandwich Panel) For Weight Saving” has been published in ‘International Journal of Engineering Research and Technology’ (IJERT) under Engineering Science and Research Support Academy (ESRSA), Gandhinagar, Gujarat. ISSN : 2278-0181 Volume-II, Issue-III, March-2013


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CERTIFICATE


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