effects of composite layer plate on modal

EFFECTS OF COMPOSITE LAYER PLATE ON MODAL EXPERIMENTAL

ANALYSIS

NUR AZLEEN BINTI ABDOL MULOK

Report submitted in partial fulfilment of the requirement for the award of

Bachelor of Mechanical Engineering

Faculty of Mechanical Engineering

UNIVERSITY MALAYSIA PAHANG

JUNE 2013

vi

ABSTRACT

The composite plates are basic structural components in aerospace, mechanical and civil

industries. This project presents the experimental modal analysis of dynamical behavior

of plates made up of woven glass fiber and epoxy matrix in free-free boundary

conditions. Two composite plates with different number of layers were analysed. The

dynamic characteristics observed are natural frequency and mode shape. The result

obtained by experimental modal analysis technique for each structure is then compared

with the result obtained by using finite element method (FEM). From the results, the

influence of number of layers on flexural natural frequencies is investigated. It shows

that as the number of layers increase, the natural frequencies also increases.

Comparative study is done between the experimental and the finite element result

obtained from ALGOR. From the ODS result, it shows that the dominant mode shape

for both four and eight layers composite plates are mode 1. The prediction of dynamical

behavior plays an important role for their future design applications.

vii

ABSTRAK

Plat komposit merupakan struktur komponen asas dalam industri aeroangkasa,

mekanikal dan juga awam. Projek ini membentangkan tentang eksperimen modal

analisis bagi mengenal pasti tingkah laku dinamik plat yang diperbuat daripada gentian

kaca tenunan dan digabungkan bersama matriks epoksi dalam keadaan sempadan bebas.

Dua plat komposit yang mempunyai jumlah lapisan gentian kaca yang berbeza telah

dianalisis. Keputusan yang diperolehi daripada eksperimen menggunakan teknik modal

analisis bagi mendapatkan kekerapan semula jadi dan bentuk mod bagi setiap struktur

kemudiannya dibandingkan dengan keputusan yang diperolehi dengan menggunakan

kaedah analisis unsure finite (FEM). Daripada keputusan yang diperolehi, pengaruh

jumlah lapisan yang terdapat pada plat komposit memberikan kesan kepada frekuensi

semulajadi telah disiasat. Keputusan menunjukkan bahawa semakin banyak lapisan pada

plat komposit, semakin tinggi nilai frekuensi yang diperolehi. Selain itu, hasil

eksperimen itu disahkan oleh unsur perisian ALGOR. Daripada eksperimen ODS yang

dilakukan, keputusan menunjukkan bahawa bentuk mod yang utama bagi empat dan

lapan lapisan plat ialah mod 1. Ramalan tingkah laku dinamik memainkan peranan yang

penting untuk mengetahui keupayaan plat komposit sebagai struktur dalam sebuah

sistem.

TABLE OF CONTENTS

Page

APPROVAL SHEET i

SUPERVISOR’S DECLARATION

ii

STUDENT’S DECLARATION

DEDICATION

iii

iv

ACKNOWLEDGEMENTS

v

ABSTRACT

vi

ABSTRAK

vii

TABLE OF CONTENTS

viii

LIST OF TABLE

xi

LIST OF FIGURES

xii

LIST OF ABBREVIATIONS

xv

CHAPTER 1 INTRODUCTION

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

5

2.2 Composite Materials

6

2.2.1 Introduction to Composite Materials

6

1.1 Introduction

1

1.2 Project Background

3

1.3 Problem Statement

3

1.4 Project Objective

4

1.5 Scope of The Project

4

1.6 Gantt Chart 4

2.2.2 History of Composite Materials

7

2.3 Classification of Composite

8

2.3.1 Continuous Fiber

8

2.3.2 Discontinuous Fiber

9

2.4 Composite Fabrication Process

10

2.4.1 Basic Hand Lay-up Technique

10

2.5 Finite Element Method

12

2.5.1 Introduction

12

2.5.2 Application of FEM

13

2.5.3 Advantages of Using FEM

14

2.6 Modal Analysis

15

2.6.1 Frequency Response Function (FRF)

16

2.6.2 Advantages of Modal Analysis

16

2.7 Natural Frequency

17

2.8 Operating Deflection Shapes 17

CHAPTER 3 METHODOLOGY

3.1 Introduction

19

3.2 Flow Chart

20

3.3 Material Selection

21

3.4 Fabrication of Fiberglass Composite Plate

22

3.4.1 Hand Lay-up Technique

22

3.5 Finite Element Analysis

23

3.5.1 Solidwork Design

26

3.5.2 Simulation Method Using ALGOR 29

3.6 Modal Analysis

31

3.6.1 Impact Hammer Testing

31

3.6.2 Modal Analysis Procedure

33

3.7 Operating Deflection Shapes (ODS) 36

CHAPTER 4 RESULT & DISCUSSIONS

4.1 Introduction

39

4.2 Result of Fabrication of Composite Plate

39

4.3 Result of Natural Frequencies

42

4.3.1 Natural Frequency by Finite Element Analysis

(FEA)

42

4.3.2 Natural Frequency By Experimental Modal

Analysis

43

4.3.3 Comparison between Natural Frequency of FEA

and Modal Analysis

44

4.4 Result of Mode Shapes for Modal Analysis

46

4.4.1 Mode Shapes by ALGOR (FEM)

47

4.4.2 Mode Shapes by Experimental Modal Analysis

47

4.5 Comparison Between Result Obtained by FEA and

Modal Analysis

47

4.5.1 Result of 4 Layers Composite Plate

48

4.5.2 Result of 8 Layers Composite Plate

51

4.6 Result for ODS

53

4.6.1 Result by Calculation (Theoretical)

54

4.6.2 Result by Experimental ODS

54

4.7 Comparing the Displacement of the Calculated Mode

Shapes

55

4.8 Comparing Mode Shapes Obtain from Calculation and 57

Experimental ODS

4.8.1 Result of 4 Layers Composite Plate by ODS

57

4.8.2 Result of 8 Layers Composite Plate by ODS

61

4.9 Discussion of The Comparison

64

4.9.1 Discussion on Result of FEA and Modal

Analysis

65

4.9.2 Discussion on Result of Calculation and

Experimental ODS

66

CHAPTER 5 CONCLUSION & RECOMMENDATIONS

5.1 Introduction

69

5.2 Conclusion

69

5.3 Recommendations 70

REFERENCES 71

APPENDICES

APPENDIX A

73

APPENDIX B

74

APPENDIX C

75

APPENDIX D

76

APPENDIX E

77

APPENDIX F

78

APPENDIX G

79

APPENDIX H

80

APPENDIX I 81

LIST OF TABLES

Table No. Title Page

2.1 Machining composites – Trade to be considered 12

3.1 Properties of the composite reinforcing fibers. 21

4.1 The frequency and displacement of composite plate with 4 layers

by using FEA

43


by using FEA

43


by using modal analysis

44


by using modal analysis

44

4.5 Comparison of natural frequency between FEA and experimental

modal analysis of 4 layers plate

44

4.6

Comparison of natural frequency between FEA and experimental

modal analysis of 8 layers plate

45


by using calculation

54


by using calculation

54


by using ODS

55

4.10

The frequency and displacement of composite plate with 8 layers

by using ODS

55

LIST OF FIGURES

Figure No. Title Page

2.1 A unidirectionally reinforced layers crossplied FRP laminate,

shows the microcracking and nonuniform fiber packing

6

2.2 Typical reinforcement type 8

2.3 Example of composites: a) particulate, random; b) discontinuous

fibres, unidirectional; c) discontinuous fibres, random; d)

continuous fibres, unidirectional

9

2.4 The basic concept in using the hand lay-up technique 11

2.5 Schematic overviewing the response problem 15

2.6 The simple plate Frequency Response Function 16

2.7 Frequency Domain ODS from a set of FRF’s 18

3.1 Methodology Flow Chart 20

3.2 Dimension of the glass fiber 22

3.3 Cutting of the glass fiber by using scissors 23

3.4 Mixing epoxy resin with the catalyst 24

3.5 A thin coat is applied on the platform before the first glass fiber is

layed out

24

3.6 Gel coat is applied to the first layer

25

3.7 Scraper used to remove all entrapped air 25

3.8 Material selection for the composite plate (E-Glass) 26

3.9 The SOLIDWORKS drawing of the 4 layers composite plate 27

3.10 The SOLIDWORKS design for the 8 layers composite plate 28

3.11 Exploded view of the four layers composite plate 28

3.12 Exploded view of eight layers composite plate 29

3.13 The analysis type of the simulation is chosen to be Natural

Frequency (modal)

30

3.14 Meshing of the composite plate 31

3.15 Example of the setup for modal testing 32

3.16 Experiment setup for modal testing, impact hammer test 33

3.17 Sensitivity setting of the hammer and accelerometer 34

3.18 DASYlab 10.0 modules for modal analysis 34

3.19 Construction of plate in ME’scopeVES 35

3.20 Numbering of points for the plate 35

3.21 Curve fitting to select the peaks from the graph 36

3.22 Example of the experiment setup for ODS 37

4.1 Four layers plate: (a) Top view; (b) side view 40

4.2 Eight layers plate: (a) Top view; (b) side view 41

4.4 The surface smoothness of the plate. (a) The unsmooth surface of

the plate (b) The smooth surface of the plate

42

4.5 Graph of comparison of natural frequency between FEA and

modal analysis for 4 layers plate

45

4.6 Graph of comparison of natural frequency between FEA and

modal analysis for 8 layers plate

46

4.7 First mode shape of 4 layers composite plate, (a) Finite element

analysis, (b) Experimental modal analysis

48

4.8 Second mode shape of 4 layers composite plate, (a) Finite element


49

4.9 Third mode shape of 4 layers composite plate, (a) Finite element


50

4.10 Fourth mode shape of 4 layers composite plate, (a) Finite element


50

4.11 Fifth mode shape of 4 layers composite plate, (a) Finite element


51

4.12 First mode shape of 8 layers composite plate, (a) Finite element


51

4.13 Second mode shape of 8 layers composite plate, (a) Finite element


52

4.14 Third mode shape of 8 layers composite plate, (a) Finite element


53

4.15 Comparison between displacement in each modes of 4 layers

composite plate

56

4.16 Comparison between displacement in each modes of 8 layers

composite plate

56

4.17 First mode shape of 4 layers composite plate, (a) Calculation,

(b) Experimental ODS

57

4.18 Second mode shape of 4 layers composite plate, (a) Calculation,


58

4.19 Third mode shape of 4 layers composite plate, (a) Calculation,


59

4.20 Fourth mode shape of 4 layers composite plate, (a) Calculation,


60

4.21 Fifth mode shape of 4 layers composite plate, (a) Calculation,


60

4.22 First mode shape of 8 layers composite plate, (a) Calculation,


61

4.23 Second mode shape of 8 layers composite plate, (a) Calculation,


62

4.24 Third mode shape of 8 layers composite plate, (a) Calculation,


63

4.25 Fourth mode shape of 8 layers composite plate, (a) Calculation,


63

4.26 Fifth mode shape of 8 layers composite plate, (a) Calculation,


64

4.27 Dominant mode for 4 layers composite plate 67

4.28 Dominant mode for 8 layers composite plate 67

LIST OF ABBREVIATIONS

FEA Finite Element Analysis

FEM Finite Element Method

DOF Degree Of Freedom

SDOF Single Degree Of Freedom

MDOF Multi Degree Of Freedom

FRF Frequency Response Function

DAQ Data Acquisition System

CAD Computer Aided Diagram

IGES Initial Graphics Exchange Specification

FFT Fast Fourier Transform

2D Two Dimensional

3D Three Dimensional

SI International System of Units

UMM Unit Modal Mass

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

Recently, there has been a lot of discussion and review about the role of

composite materials as the one of the most common material used in a lot of the

growing industries that exists today. Some of the most common use of composite

materials in everyday life would be sports equipments, ship building, automobile,

and aircraft.

There are many types of composite materials used in the industries. Fiber

reinforced composite materials includes glass, carbon, aramid, boron and also

ceramics (Tsipas et al, 2012). The fibreglass is one of the types of composite. There

are divided further by the types of fibreglass. In this study, the woven fabric

composites will be used during the experiments. The application of this woven fabric

composites are wide especially in the engineering application. The benefit of using

woven fabrics as the reinforcement is that it provides conformability and also

excellent integrity for any advanced structural composite application (Mishra et al,

2012).

Since the application of the composite materials are more onto the structures

of the automotive, aircraft, shipbuilding and mass transit bodies, subjected widely to

dynamic loading that can cause excessive vibration (Velmurugan et al, 2011). To

determine the different modes of vibration, the dynamic response of the composite

structures need to be understood and studied.

2

Due to the advancement on the computer aided data acquisition system and

instrumentation, it has become more important for the experimentalist to do

experimental modal analysis (Sahu et al, 2012). There are many researchers that did

the research on the laminated composite laminates, but the research on the dynamic

characteristics of the woven fabric composite laminates are still limited.

The method that will be used to test the woven fabric composite would be by

modal analysis using the FFT (Fast Fourier Transform) analyzer. This study will

involve the experiment on the woven fiber Glass/Epoxy composites plate. The

specimen will be in free-free boundary condition form.

The woven fabric composite specimens are fabricated by using the hand-

layup technique. The material required for the fabrication of the composite plates are

E-glass woven roving which act as the reinforcement (Owens Corning) , Epoxy as

the resin and hardener as catalyst.

The composite will have different number of layers. The effect of layers in

the composite will be determined by using the modal analysis experiment. The result

from the FFT analyzer will then be compared with the Finite Element Method (FEM)

tool ALGOR. The results will lead to the natural frequency of each of the different

layer composite and the modal shape can be obtained by the ANSYS (Stanciu et al,

2011).

The prediction that the FEM tool ALGOR produce is important when

comparing with the FFT result. There should not be much difference in the natural

frequency data during the comparison. The study of this dynamic behaviour and

characteristics of woven composite plates plays an important role for the future

application of this material.

3

1.2 PROJECT BACKGROUND

Since there are not that many studies directed on the composite materials, the

dynamic characteristic of the composite material itself are hard to find.

Composite materials are widely used in a lot of the developing industries

today. Some of the industrial sectors that use composite materials are aerospace,

automobile, boats, chemicals, domestic, electrical and leisure. In aerospace only will

consist of a lot of composite materials such as wings, helicopter blade, landing gears,

seats, floors, interior panels, fuel tanks and nose cones (Rawlings et al, 2006).

As stated above, the application of the composite materials is important in

many industries. So, in order to gain the valuable information about the dynamic

characteristics this study need to be done. The effect that the different geometrical

parameters especially the number of layers in the free-free boundary condition of the

woven fabric composite plates can be known (Mishra et al, 2012).

1.3 PROBLEM STATEMENT

In recent years, the study about dynamic behaviour of the composite

materials has become significant due to the increasing demand in the industries. The

natural frequency of the material should be known to prevent any disastrous impact

for any engineering structure. Fiberglass material is considered as a safe material to

be used, but the damages in the material itself are rather hard to be detected. So, it is

really important to know the factors that contribute to the danger that can be

catastrophic (Chang et al, 1992). The main reason this study is made is to produce a

better understanding of the dynamic behaviour that are made from the woven fiber

composite materials especially for the plates. The effects of different number of layer

in the composite plates in free-free boundary condition are studied in detail.

4

1.4 PROJECT OBJECTIVE

The objective of conducting this project is to study the dynamic properties

and behaviour of composite layer by using modal analysis and finite element

analysis.

1.5 SCOPE OF THE PROJECT

The scope of carrying out this project includes:

i. The analysis of fibreglass composite will be carried out by using Finite

element analysis tool ALGOR.

ii. The type of composite use would be fibreglass as the reinforcement and

epoxy as the resin.

iii. The experimental result will be obtained by model testing by using impact

hammer.

iv. The experimental result and the computational result will be compared.

v. It is the analysis of the natural frequency by using model analysis and FEM

on the composite plate to find out the mode shape and natural frequency.

vi. Experimental Operational Deflection Shape (ODS) by motor of 53Hz.

vii. Validation of experimental ODS is done by using calculation and the result is

compared.

1.6 GANTT CHART

The Gantt chart is illustrating the project schedule. The starting and finishing

week of the project is stated in the chart. It is divided into two rows for each

progress. The first row will illustrate the planned period for the element while the

second row is the actual period that is done to complete it. The Gantt chart for this

particular project can be referred to Appendix A

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

In this chapter, the explanation about the project will be stated in detail. It

started off with the introduction to the composite materials. Since the composite

material itself has many types, the classification of the composite material will be

explained further. The main focus would be for the E-glass woven roving which will

be used in the experiment.

Other than the explanation on the composite material, there will also be some

discussion on the modal analysis itself. Since the experimental investigation will be

carried out by using modal analysis technique with the Fast Fourier Transform,

DASYLab, impact hammer and also the triaxial accelerometer, the explanation will

go deeper in order to give a clear view on how the process will flow and also the

connection between all of the elements stated.

Moreover, Finite Element method (FEM) tool ANSYS will also be explain in

detail in order to show the function of using this particular software. This tool is

needed so that the result can be compared with the FFT analyzer.

6

2.2 COMPOSITE MATERIALS

2.2.1 Introduction to Composite Materials

Composite material actually can be define as the combination of two or more

materials that will eventually produce a product with better properties than those

individual components stand alone (Campbell, 2010). It is different than the metallic

alloy. This is because the alloys can actually blend the characteristics and properties

of two or more metals in order to create a hybrid metal that is more stronger, durable

cost-effective than the pure metal. Metal alloys are different from composite

materials because there will be subtle changes in the microstructure which will cause

dramatic variations in their properties (R. Saravanan et al, 2012).

Composite can be define by a lot of different thing if it is taken at the face

value but in the more modern materials engineering, it can be referred to “matrix”

material which is reinforced by fibers. By taking Fiber Reinforce Plastic (FRP) as an

example, the term indicates that thermosetting polyester matrix that contains glass

fibers (Roylance, 2000). Figure 2.1 is showing the laminate fabricated by

unidirectionally crossplying reinforced layers in a 0 ̊-90̊ stacking sequence.

Figure 2.1: A unidirectionally reinforced layers crossplied FRP laminate, shows the

microcracking and nonuniform fiber packing.

7

Source: Harris, B., Engineering Composite Materials, Institute of Metals, 1986.

Composite material is not something that is new to the material engineering.

In fact, the first uses of composite went back to the 1500s B.C. It all started when the

Mesopotamian and Egyptians used the mixture of straw and mud to build stronger

and more durable buildings (Todd Johnson).

2.2.2 History of Composite Materials

The first ever binding materials that were employed to fabricate mortars in

ancient buildings would be mud (Moropoulou et al, 2005). This means that

composite is not really a new technology. This is because even the bricks that are

reinforced with straw and made from mud that were used in ancient civilizations are

also considered as composite (Matthews et al, 2006).

The modern composite industry began in 1930, when it is made almost by

accident. This happened when an engineer became interested by the fiber formed

during the process of applying lettering to a glass milk bottle. Then, in 1937,

salesmen from the Owen Corning Fiberglass Company began selling their fibreglass

in the United States to the interested parties. This company was formed in 1935 by

Owens-Illinois and Corning Glass Works to focus on selling the new fibrous material

(Brent Strong, 1989).

The second generation of the composite starts in 1960s where the composite

is already called the high performance composite. During this era, a new Saint-

Gobain factory in Chambery, France was opened for the production of fibreglass. By

1958, they started to produce composite helicopterblades especially for Alouette II.

At the same time, carbon, boron as well as aramid fiber were also introduced to the

world. Aramid fiber also known as Kevlar is actually discovered after Kwolek tried

to find a solvent to dissolve the nonmelting polymer that she made earlier. This

discovery actually proved that the fiber produced from the aramid solution is actually

five times stronger than steel. It can be applied to bulletproof vests and helmets (Tim

Palucka et al, 2002)

8

2.3 CLASSIFICATION OF COMPOSITE

2.3.1 Continuous Fiber

Continuous fibers have long aspect ratio. Aspect ratio is the length-to-

diameter (l/d ) ratio. However, continuous fibers can have varied aspect ratio

considerably (Rawlings et al, 2006). Continuous fiber composites will usually have

the preferred orientation. The orientation of continuous fiber can be seen from Figure

2.2. Some examples of continuous reinforcements include unidirectional, woven

cloth and helical winding.

Figure 2.2: Typical reinforcement type: a) continuous fiber; b) discontinuous fiber

Source: F.C. Campbell, 2010.

9

2.3.2 Discontinuous Fiber

Discontinuous fiber can also be known by particulate composite. Particulate

reinforcement may have the dimensions that are more or less equal in all direction.

They can come in many shapes including spherical, cubic, platelet, or any irregular

or regular geometry (Rawlings et al, 2006).

Comparing to the continuous fiber, particulate seems to be much weaker and

less stiff, but they are not as expensive as the continuous fiber. Discontinuous fiber

have short aspect ratio and they usually have random orientation (Matthews et al,

2006). Examples of discontinuous fiber are chopped fibers and random mat which

can be seen in Figure 2.3.

Figure 2.3: Example of composites: a) particulate, random; b) discontinuous fibres,

unidirectional; c) discontinuous fibres, random; d) continuous fibres, unidirectional.

Source: Frank L. Matthews, Rees D. Rawlings, 2006.

10

2.4 COMPOSITE FABRICATION PROCESS

2.4.1 Basic Hand Lay-up Technique

It is normally done in a Fibre Reinforced Plastic (FRP) mould that are

polished on the inside part. There is no limit when it comes to the mold. Some may

be as simple as flat surface or some may have infinite edges and curves (Brandon

Lee, 2004). Figure 2.4 shows the basic hand lay-up technique.

Hand lay-up is considered as the simplest and oldest way used to produce

reinforced plastic laminates. The capital investment for using this method is

relatively low comparing to other method. For simplicity, some fabricators may used

brush or simply pour the resin into the molds if spray gun is not available. Spray gun

is the most expensive equipment for hand lay-up process, but it is optional to do so

(American Composite Manufacturers Association, 2004).

Figure 2.4: Basic concept in using the hand lay-up technique.

Source: J.R. Vinson, R.L. Sierakowski, 2008.

11

The very first step to do the hand lay-up is preparing the mold for the

composite to be applied on. The mold should be clean and free from any surface

deformation or particulate because it can affect the final surface condition of the

composite itself. Check the mold from chips and blemishes.

Next step is applying the releasing agent on the surface of the mold so that

the composite can be released easily after curing (Brandon Lee, 2004). Releasing

agent is actually a non-binding polymer or a wax that is first coat to the mold. This

releasing agent can ensure easier release and pop out of the finished cured part from

the mold (Todd Johnson). Some examples of releasing agents are poly vinyl alcohol

(PVA), hard wax and fluorocarbons (Keith Godber, An Overview of Release Agent

Types and Technology).

Resin is another important part in making composite. Resin will hold

everything together while transferring the loads that are applied on the composite

through the fibers to the rest of the structure. Other than the purpose of binding the

structure, resin will also protect it from any kind of corrosion, abrasion, impact and

also environment factors (Fibermax Composites, 2007). Among the most commonly

used resin would be Polyester (orthophthalic and isophthali), epoxy, phenolic and

also vinyl ester. The mixture of resin and the catalyst should be in the correct

quantity which is between 11 2 - 2% when comparing by the weight (Basic Hand

Lay-up Techniques For Reinforced Composites).

Ideally, the lay-up process of the fibreglass reinforcement should start as soon

as the mixture of resin is ready (Basic Hand Lay-up Techniques For Reinforced

Composites). This is because if the time lapse between the lay-up and mixing the

resin is too long, the resin will hardened before it could reached the fiber. This can

produce a low quality composite as a final product. The hand lay-up process can be

done by using brush or even spray gun (American Composite Manufacturers

Association, 2004). From Figure 4, it can be seen that a roller is used to take out all

of the air bubbles from the laminate to ensure even resin deposited and no air bubbles

in the composite.

12

The curing part of the hand lay-up technique is done after the fibreglass

reinforcement and resin finished. The curing time for different composite may varied

according to the size, thickness and type of composite. The curing may be as fast as

two hours or it could even be cured overnight. Upon curing, the composite can be

trimmed according to the desired size and shapes (Beckwith, 2009) as shown in

Table 2.1.

Table 2.1: Machining composites – Trade to be considered

Source: W. Beckwith, 2009.

2.5 FINITE ELEMENT METHOD

2.5.1 Introduction

Finite element method (FEM) is a method that uses numerical to solve

integral or differential equation. A lot of physical problem has applied to this method

effects of composite layer plate on modal

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