FIBER REINFORCED

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INVESTIGATION ON THE EFFECTS OF DAMAGES ON THE FLEXURAL STRENGTH OF GLASS FIBER

REINFORCED PLASTICS (GRP)

MARINI BT SAWAWI

Universiti Malaysia Sarawak 1999

TA 417.2 H337 1999

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Borang Penyerahan Tais Univeniti Malaysia Sarawak

BORANG PENYERAHAN TESIS

Judui: INVESTIGATION ON TIIE EFFECTS OF DAMAGES ON THE FLEXURAL STRENGTH OF GLASS FIBER. REINFORCED PLASTICS (GRP)

SESI PENGAJIAN: 1996197

Saya MARINI BT. SAWAWI

(BURUF BESAR)

mcngaku membc:narkan tcsis ini disimpan eli Pusat Khidmat Maldumat Akademik. Univcrsiti Malaysia Sarawalc dengan sylD1It-syarat kegunaan sepcrti bcrikut:

1. Hakmilik. kertas projek adalah di bawah oama peuuIis melainkan penulisan sebagai projek bersama dan dibiayai oleh UNIMAS, bakmiJjknya adaIah kqrunyaan UNIMAS.

2. Naskhah salinan di dalam benluk. kertas aI.au milao baIlya bolch dibua1 dengan kebe:aanm bertuJis daripada peoulis.

3. Pusat .Khidmat Maklumat Akademik, UNlMAS d.ibeoarkan membuat salioan untuk pengajian meceka.

4. Kertas projek baoya bolch ditabitkan dengan kebeoaran penulis. Bayaran royalti adalah mengikut kadar yang dipcnetujui kclak.

5. • Saya membalarkmItida IIICIIlbcruIrkm Papustaban manbuat salinan kcrtas projc:k ini scbagai baball patukaran di aoIara institusi pcngajian tinggi.

6. •• SilA tandakan ( ./ )

I I

^SULIT (Mcngandungi maklumat yang berdlpjah keselamatan atau kepentingan Malaysia sepc:rti yangtennaktub eli dalllJ1l AKTA RAHSTA RASMT 1972).

(Meogarubrogi maklumel TERHAD yang lelab dilco'ukan oleh orgBDisasil badan di ID8II& pcoyclidikan dijalankan).

~ TlDAKTERHAD

Disahkan oleb

(TANDATANGAN PENYELIA)

AIamat lelap: NO 22, LG.^1l

14,

^KG

SEMARIANG BATU.

93050 KUCHlNG

Dr. HA HOW UNG

Nama Pcnyclia

Tarikh: 13 - 5 -1999 Tarikh: 13-5-1999

CATATAN· p. . . .,...,tiUklMln--

JIb Ke... PmJek InI SULIT .... TERHAD, . . ....,...u. ... ^pIUkberkDual ... ItcrllirMaa daIpa IIICII,eI1lllwl IdWI . . . Irmu ,rojek. Ial pcrIII .tilq:tnkM

. . . . SlJur ... "fERRAD.

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This project entitled "Investigation on The Effects of Damages OD the Flexural Strength of Glass Fiber Reinforced Plastics (GRP)" was prepared by Marini bt.

Sawawi as a partial fulfillment for the Bachelor of Engineering (HoDS) Mechanical Engineering and Manufacturing Systems degree programme is hereby read and approved by

Dr. Ha How Ung (Project Supervisor) Date:

r~ l s1 '11

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"usal Khidmal Maklumaf Akademik JNIVERSITI MALAVS A SARAWAK

P. KHIDMAT MAKLUMAT

II

_OOOOO?

Investigation

On

The Effects OfDamages

On

The flexuraf Strength OfGlass Fiber Reinforced Plastics (GRP)

PUMT JallDMAT MAJ(LUMAT AKADI:MIK UNlVER8m MALAYSIA SARAWAK

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This

repOrt

is submitted 8S a partial fulfi11ment ofthe requirement for the degree of

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Bachelor ofEngineering (Hon$) Mechanical Engineering and Manufilcturing Systems from the

Faculty OfEngineering Universiti Malaysia Sarawak

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Dedicated to my beloved family

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ACKNOWLEDGEMENTS

The author would like to express ber gratitude and appreciation to her Project Supervisor, Dr Ha How Ung for bis guidance, encouragement and thoughtful tips throughout the duration ofthe project.

Furthennore, the author would like to thank: her lecturer, En. Nazeri, and En. Wan Ali, from Forestry Department, Mr. Thien Ek L~Managing Director of Vertex Fiberglass, Not forgetting the Laboratory Assistant; En. Masri, En. Rhyier and Haji Affendi for their

help

in C9Ild~g ~ exper1~ In addition.

the swtbor

vrouJd ]~e

to specifically thank

her family for giving their s~ help and encouragement during difficult encounters while -doing her laboratol)' research and report writing. Million thanks for everyone, who

had involved directly or indirectly to make this project successful.

III

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Pusal Khidmat Maklum t Ak:.ademik

tJNlVERSITl MAl. YSIA SARAWAK

BIBLIOGRAPHY 49

AppeDdix 1 51

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Appendix 2 52

Effect of shape of hole on the stress concentration factor for a bar with transverse hole

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LIST OF TABLES

3.1

3.2

TABLE

Physical Properties of A Typical Polyester Laminate Made From ABM IITX Mat

Specification of specimens

PAGE 29

29

VII

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\

LIST OF FIGURES

FIGURE PAGE

1.1 Basic building block in Fiber Reinforced Composites

5

1.2

Common forms ofglass fibm; 6

1.3 Strength ofDiffe~Types QfRei~t 9

2.1

Buckling failure II

2.2 Classification of fracture morphology from macroscopic view 12 2.3 Classificationoffmcture morphology ofreinfoo=ement tiber from

15

miCfQS(:()ptc latetal view

2.4 Oassitkationoffracture morphology offiber end from 15 microscopic view

2.5

Fracture process ofunidirectional carbon fiber reinf~plastic in 16 the case ofX300

2.6

Longitudinal stress distributions 18

2.7 Possible micr.ofailure modes following the breakage offiber 3. 19

2.8

Fracture surfitre ofa mndOmly discontinuous fiber composite 20

.. "

showing the evidence offiber pullout

2.9

3 point bending flexural tests

21

2.10

Efti:ctd impactenergy (1).on the flexural strength ofGRP after

22

·oneimpact

2.11

Photograph oflaminate failure illusuating

uan.werse

shear mck

22

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and delamination phenomenon

2.12

Microscopic view :Debonding between gJa$s fibers

23

2.13

Microscopic view: Oelammation between plies 23

2.14

COlUpBlison for SIN cmves for Unootcl1ed and Specimens with

24

Central Holes 3mm in Diameter

2.15

Failure modes for (a) unnotched ^spc;c~

an4

(b) ~imenswith

5

a central hole

2.16

Common failure modes for mechanically joint composites.

26

3.1 Different condition of specimens 30

3.2

( left -

right)

Dartec

software, Monitor,

Universal

Testing

31

Machine

3.3

3 point bending test

32

3.4 Different location ofspecimen to be tested 34

3.) Cold

Mounting Equipment

35

3.6

Readily mounted specimen

36

3.7 Surface finishing; grinding and polishing

36

4.1 Area in specimen C and D without defects

39

4.2 Damajes

aligning

the fiber

41

~,

4.3

Fiber breakage in specimen

42

4.4

Fine cut of the hole edge

43

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ABSTRACf

This project investigates the effects of damages on the behavior ofGlass Fiber Reinforced Plastics (GRP) under flexural loading. The damages are introduced by drilling of holes for tastening purposes where two specimen are bolted together. This investigation does not take the manufucturing defect into 8CCOWlt Thus. the extend of damages ^wassolely due to those initially induced on the material. This project involved laboratory works where the specimen was subjected on a cyclic flexural loading of 7500 cycles at a frequency of O.5Hz. Subsequently, the extend of damages was detennined by using section method where the specimen was mounted using cold mounting resin and metaUurgica1.investigation from the result, it shows that the extension of damages for each of the specimen varies although it experienced the same flexure loading. It can be concluded that the extend ofdamages depend on several factors such as nmnber of holes, orientation of multifastener and quality of drilled holes. As a conclusion, the joining of GRP by mecbanicaljoint is reliable and applicable

utile

factors mentioned above is taken into consideration.

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ABSTRAK

Kajian in membincangkan tentang kesan kerosakan plda bahan komposit iaitu 'Glass Fiber Reinforced Plastics (GRP), apabila dikenakan beban lentur. Kerosakan yang dibuat adaJah disebabkan oleh lubang untuk tujuan sambungan bolt

Jllda

dua bahan tersebut.

Dalarn anaIisis ini, kerosakan semasa pembuamnnya adalah tidale di ambl1 kira. Dengan itu, perambatan kerosakan adaJah disebabkan kerosakan yang dibuat tadi. Analisis ini melibatkan kelja makmal di mana spesimen dikenakan beban lentur berkitar iaitu 7500 kitaran. Kemudian, bahan tersebut akan diperiksa dengan cam 'section method' dimana spesimen tersebut akan di cagak sejuk menggunakan resin. Daripada keputusan, didapati walauptm semua spesimen tersebut menga1ami beban lentur yang sarna., namun perambatan kerosakan plda setiap spesimen adaIah berbeza. Tni disebabkan oteh, perambatan kerosakan dipengaruhi beberapa fBktor iaitu bilangan lubang yang digerudi, kesan samblDlgan bolt serta kualiti tubang tersebut. HasH analisis ini mendapati bahawa, sambungan mekanikal contohnya bolt adaJah baik sekiranya faktor yang dinyatakan di atas diambil kira sebelum membuat sambungan.

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,...

CHAPTER 1

INTRODUcnON

1.1 Overview

This project investigates the effects of damages on the flexure strength of glass fiber reinforced plastics. The behaviors of GRP in particular, under flexure loading condition have not been widely investigated and there are problems in obtaining the information on this particular

area.

In this project, damages were introduced on the composite material intentionally. These damages were introduced by drilling of holes for fastening purposes where the GRP specimen will be bolted together. The joining of these materials by using boh are considered to be undesirable because the holes may cause damages to the fibers and at the same time resulting in the introduction of stress concentration around the bolt holes.

The design methods established for structural joints in metals are applialble in general to

GRP jo~ the physical nature _ the materials however does introduce problems not

generally encountered with metals. The anisotropic stiffness and strength mean that unexpected failure modes may .also be introduced. Material and geometrical characteristics of composite materials, mction force and clearance between fastener and composite materi~ fastener stiffness combined, led to the determination of stress distributions becoming more complicated. The local contact between the mechanical

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fastener and composite iaminatemayinducelargestrain -and high stress near the edge of the hole-andeventually lead to failure ofthe laminate [1].

For the purpose ~fthis-study, -the -effects due to the manufacturing ·defects are -not ·being investipted. Thus, the project will only investigates the extend of damages induced on the material and their effects -on the flexure behavior ofGRP.

1.2 Objectives

The objectives of this project are to determine the effects of damages -on the flexural strmgtbro {,JRP _and _al,~ me.,c;tablisb a relationship on the extent of damages and the flexural behavi~ with respect to different -condition -such as the -orientation -of -the damages (holes) induced and multifastcners joint of the GRP.

1.3 DefiDitioB OfTfl'IIIS

1.3.1 Composite Materials

Fiber-reinforced composf~ materials consist of fibers of high -strength and modulus embedded in or bonded to a matrix with distinct :interfaces betweeJJ them. In this folln, both fibers and matrix have their physical and i::hemical identities. yet tbeyproduce a combination of properties thatcarmotbe achieved with dther of constituents acting al-one. In general, fibers are principal load

carrying members, while the sUITOlUlding matrix keeps them in the desired

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location and orientatio~ acts as a load transfer medium between them, and protects them from environmental damages due the elevated temperatures and humidity , for example. Thus , even though the fibers provide reinforcement for the matrix , the latter also serves a number of useful functions in a fiber reinforced composite material.

The most common form in which fiber-reinforced coJJJpm;i~~ are u~d in structural applicatioos is call 1amiMte. It is obtain by stacking a number tlf thin layers 1)f fibers and resin -matrix -and consolidating them 1m1) the desired thickness.

Fiber -orientation in each layer -asweH -as the stacking sequence 'Of various layer can be controlled10 generate a wide range ofphysjcaJ and mechanical PJo~rtjes

The properties of a fiber-t'dnforted composite depends -strongly 'on 1he 'direction

9f~for ~ample. the tensile -strength and modulus ofa unidirectional oriented fiber-rcinfor«d laminated are maximttm. wheB ·the ·pr6perties are measured along the longitudinal directioo of fibers. At any other angle 1)f measurement these proP!2!ies are lower .

. ' ,

The design ofa.fiber-reinf«ced structure is considerably more difficult than that of metal structure, principally due to the difference in its properties in -different directions. However, anisotropic nature of fiber-reinforced composite material creates a unique opportunity of tailoring its properties according to the de:tign

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sat Khidniat MUkJumut Jrudemik IVERSITI MALAYSIA SARAWAK

requirements. This design flexibility can be utilized to selectivity reinforced a structure in the directions of major stresses, increase its stiffness in a preferred direction, fabricate curved panels without any secondary forming operation, or produce with zero coefficients ofthermal expansion(2].

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CONSTiTUENTS

FI3ERS + MATRIX + COUPLING AGENTS + FILLERS OR COAT!NGS

~ LAMINA (PLY ^J LAYER)

} (a) UNIDiRECTIONAL CONTINUOUS

I

I I 1 !

( r ,ⁱ

(b) SIDIRECTIONAl CONTINUOUS ( r

f

/ I r [ r

~

(e) UNIDIRECTIONAL DISCONTINUOUS

(d) RANDOM DISCONTINUOUS

(e) LAMINATE

..

^'

~

Figure 1.1 Basic building block in Fiber Reinforced Composites

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1.3.2 Glass fiber

Glass fibers are inorganic, synthetic, multifilament material. They are the most common ofall reinforcing fibers for polymeric {plastic ) matrix -composites. Glass fiber composites are strong, low in cost:. nonflammable, nonconductive (electrically), and corrosion-resistant. The disadvantages include low tensile modulus, relatively high specific gravity {among the commerc.ial :fibers)~

-seDSitivity to abrasion with handling { whkh frequently decreases tensile strength), relatively low fatigue resistance, and high hardness -( which -causes

exussive wear -on mokting dies and cutting toots). An example -of :commonly used glass fiber is E-glass.{3]

Chopped mands mat

CORtinuous ttraDdr-Ovina -wovenr0vinl

Fipft 1.2 Common forms

of

glass fibers 6

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1.3.3 Polymeric matrices

The role of matrix in the fiber-reinforced composjtei:; ^l()tran~fe.r .stre.~~e.sfletwe~

the fibers and to provide a barrier against an adverse -environment. It also used to protect the -surface of the fibers from mechanical abrasion. The matrix -plays -a minor role in the tensile toad -canyingcapacity of a composite 'Stmcture. The

. 'deS.lateraJ . tb_ PQ.-ssibT_ __ _ JlUCklin - d_

matnx pro^{V )} ¹ support agamst e. ^_ ^IJry^(t^f^fiber^_ ^_^-l.. ______ gUll e.r compression loading. thus influencing to wme -extent the compressive strength of the composite material. For this particuJar study, polymer matrices -are -used A polymer 1S defined -as a long chain molecule containing one or more repeating units of atoms joined together by strong covaJem -broJdc;- A poJymcric ma..tcriaf (rommooly ailed a plastic) is a collection tlf' a large number of polymer

molecules of similar chemical structure (but not equal length).

1.3.4 Applicaticm

The major structural application areas of fiber reinforced plasticinelude -aircraft, automotive. sporting goods and marine engineering. It is mainly used because it offers weight reduction.

~~ensionaJ

stability over a wide

temperatQf~ Jaoge~d

vibration damping. The unique combination of mechanical properties -such as lower specific gravity andbigher strength as well has led a number tlfapplications for this composite in artificial satenite.

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1.4 Types Of Fiber Distribution

Fiber distribution in composites affects the mechanical properties of composites. This is

because, thefi-beris tlsedto alter the crack propagation of -composite -materials. -If-the dircctionof the load and the fiber is not the same, then the load cannot be transferred effectively to the fiber, thus the crack win propagate in the matrix. There -are -three -major types of fiber distribution avai1able. which are:

a) RancWm distribution

For random distribution. usually the fibers are very -short. The fibers -commonly -used are chopped strand ~ which is usually

2OJ.1D1

in length and also the cheapest fiber. In

composite materiaJs, -it -is 1-0-50010 {by weight). :hJ J"andom ..dimibntiOll, ;if;tbe.Jlirection..of the fiber is the -same as the direction of the load, then the lead can be transferred to the

fiber. Random distribution offers the lowest strength -compared -to -other -categories -of reinfortement.

b)- entiAUGUS distributioa.

An example of continuous fiber is woven mat, where the fiber is 90° to one another. The strength of-continuous fiber is ^greaterthan random distribution.

e) Unidireetional

In wricfuecnonaJ distribution,)t the ,fibers are in one direction. It -offers thehigbest .strength if we compared -to other categories

m

reinf-orcement. However, this type

m

distribution is expensive to produce.

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Streaath,crl'

unidirectional

continuous

Volume,

vr

Figare 1.3 Strength ofDifferent Types ofReinforcement

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CHAPTER 2

LITERATURE REVIEW

2.1 Oftrview

The literature will emphasize on the behavior of composite materials under tension, -compressionandalsotlexuralloading. There would also be an analysis of mechanically

joint composite -

to

-relate it-with

the case-in

-

this -project

1.2 Compressioll Effects

The compressive strength of fiber -composites is often less than the -tensile strength and 1I1us can-be;\imiting-factorin:stJ~-E1h..;criti-cai applications. In comptessive faiiure, matrix plays an important role as the dry fibers would not support a compressive 1oad. There are two different types of deformation modes during compression, which are buckling and

material. Material is a general term used to describe the failure of composite materials by

-IeVeral:~ _.sucbas matrix cracking, fiber fracture, intelface -mear faiiure and delamiDation[4]. There are two

:-~

^ofbuclding failure which are -extension mode and shearing modes[ 1].

a) Extension mode

In extension mode the strain energy

m

the -matrix lS assume to be dueen:t~relyto tmnsverse normal stresses tbatare taken to be uniaxial and uniform in the transverse direction.

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