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Mustafa Akay An introduction to polymer-matrix composites 2 Download free eBooks at bookboon.com An introduction to polymer-matrix composites 1st edition © 2015 Mustafa Akay & bookboon.com ISBN 978-87-403-0980-5 3 Download free eBooks at bookboon.com An introduction to polymer-matrix composites...

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Manufact uring processes and mat erials Akagu Clarence

Int roduct ion t o Polymer Science and Technology - in English Douglas Benício Int roduct ion t o polymer science and t echnology zeineb wahada

Mustafa Akay

An introduction to polymer-matrix composites

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An introduction to polymer-matrix composites 1st edition © 2015 Mustafa Akay & bookboon.com ISBN 978-87-403-0980-5

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An introduction to polymer-matrix composites

Contents

Contents Preface

8

Acknowledgements

11

1

Introduction

12

1.1

Case for composites

12

1.2

History of the development of composites

15

1.3

Classification of composites

19

1.4

Composite constituents

25

1.5

Self-assessment questions

62

2

Processing and forming methods

66

2.1

Open-mould processes (Contact moulding)

66

2.2

Closed-mould processes

78

2.3

Wood-plastic composites

91

2.4

Other processing considerations

100

2.5

Self-assessment questions

112

360° thinking

.

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An introduction to polymer-matrix composites

Contents

3

Estimation of mechanical properties

114

3.1

Continuous fibre composites

114

3.2

Short (discontinuous) fibre composites

122

3.3

Failure mechanisms that result in composite toughness

126

3.4

Self-assessment questions

137

4

Mechanical and thermal properties

142

4.1

Introduction

142

4.2

Tensile properties

144

4.3

Compressive properties

146

4.4

Flexural properties

148

4.5

Shear properties

150

4.6

Impact and fracture toughness properties

152

4.7

Bearing strength

164

4.8

Fatigue and wear

168

4.9

Differential scanning calorimetry

188

4.10

Dynamic mechanical thermal analysis

191

4.11

Environmental effects on properties

199

4.12

Non destructive evaluation

209

4.13

Self-assessment questions

213

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An introduction to polymer-matrix composites

Contents

5

Applications and materials selection

215

5.1

Applications

215

5.2

Materials selection

255

5.3

Self-assessment questions

272

References

274

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To my parents (Rahmatullahi Aleyhima), to my wife, and to Mevlüde, Latifa and Melek, the apples of my eye

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An introduction to polymer-matrix composites

Preface

Preface Learning involves acquiring knowledge, which is encouraged in all traditions. For example, the Quran urges people to seek knowledge and to use it for the well being of society: “My Lord, increase me in knowledge”, Al-Quran 20:114. “Ignorance is the curse of God; knowledge is the wing wherewith we fly to heaven”, William Shakespeare. Knowledge should be applied in a safe, responsible and ethical manner not only to benefit us personally but also to improve the lot of the people we live with. It is also a duty to ensure that our surrounding habitat is not endangered. This sometimes requires knowledge of the local culture to help achieve a desirable outcome. Martin Palmer’s presentation on BBC Thought for the Day programme, 17/06/2006, on the subject of the protection of the oceans included: “To many around the world the environmental movement and its proffered solutions – usually economic – are alien ways of thinking and seeing the world, and can be interpreted as telling people what is best for them whether they like it or not. Let me tell you a story. Dynamite-fishing off the East African coast is a major problem. Environmental organisations have been addressing it for years, from working with Governments, to sending armed boats to threaten those illegally fishing. None of this worked because it had no relationship to the actual lives or values of the local fishermen all of whom are Muslims. What has worked off one island, Misali, is the Qur’an. In the Qur’an, waste of natural resources is denounced as a sin. Once local imams had discovered this, they set about preaching that dynamite fishing was antiIslamic, non-sustainable and sinful. This ended the dynamite fishing of the Misali fishermen because it made sense to them spiritually.” The perception/foresight of Canadian scholar, Wilfred Cantwell Smith, is also relevant in this context, particularly these days when there is so much misunderstanding and misrepresentation about peoples of different religions and cultures. Regarding Muslims, Wilfred Cantwell Smith in his book Islam in Modern History (Princeton and London, 1957. p. 304) says, “the Muslim segment of human society can only flourish if Islam is strong and vital, is pure and creative and sound”. Practice of pure, creative and sound Islam by its followers will be for the good of all.

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An introduction to polymer-matrix composites

Preface

The contribution of materials science to society now and in the future is highlighted by many eminent scientists in the Japan Society for the Promotion of Science publication of “Science and Society”. Sir Colin Humphreys of Cambridge University (1997, p. 34) in his article indicates how material science is really enabling the lame to walk, saving lives, transforming the world energy scene and generating wealth and employment, and states that materials science is a key for our future health and our future wealth. Examples he gives include medical implants, shape-memory metals and the potential use of carbon fibre-based light tethers to facilitate deep sea exploration/extraction of oil or gas beyond depths of 1,500 metres (in deeper waters, longer lengths of steel ropes are needed to tether the rigs, which necessitates more and more buoyancy to prevent the rigs from sinking). His article also alludes to the famous science fiction writer Arthur C. Clarke, who envisaged a situation where there is a satellite above the earth, in a geostationary orbit, tethered to the earth by a carbon fibre rope, with a lift on the rope (the Space Elevator) which would ferry people up and down to the satellite. That was thirty years ago and his predictions might be coming true! Back on earth, however, and across the seas, another application of carbon fibre ropes is suspension bridges. Seventy per cent of the weight of a suspension bridge is in the steel cables. As bridges get longer and longer, they can no longer hold up their own suspension cables. The maximum length or span, of a conventional suspension bridge is 5,000 metres. If the steel ropes are to be replaced with carbon fibre ropes however, then one can calculate that the maximum span goes up by a factor of three. In principle, one could have a suspension bridge which is 15,000 metres long. The story of carbon-based materials continues to unravel: in his recent book, Miodownik (2014, p 198) introduces the story of graphene and describes his visit to Manchester University to see Andre Geim, a joint discoverer of graphene. Andre’s team received the Nobel Prize for demonstrating that single layers of graphite had properties that were extraordinary even by nanotechnology standards – so extraordinary that they merited their own name as a new material: graphene. Miodownik states, “this material and its rolled-up version in the form of nanotubes are going to be an important part of our future world, from the smallest scale to the very largest, from electronics, to cars, to aeroplanes, rockets and even – who knows? – to space elevators. Although it appears likely that graphene will usher in a new age of engineering, and indeed scientists and engineers are in love with this material already, this may not give it high status in the world at large. Diamonds may not be the hardest, strongest material any more, and we know that they will not last for ever, but they still represent those qualities to most people.” The subject of this book reflects the strong relationship between material structure, properties and applications. Changing one affects the others and this has enabled scientists/engineers to tailor materials to suit purposes. The dependence of properties on the structural arrangement of material is so obvious in composites as demonstrated by the ancient Egyptians, who invented the process of cross-grain laminating veneers of wood.

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An introduction to polymer-matrix composites

Preface

Chapter 1 is a broad introductory chapter and includes a history of the development of composites; classification of composites; constituents of polymer-matrix composites; the fibre-matrix interface, and fibre arrangement. The subsequent two chapters deal with processing and forming methods, and estimation of mechanical properties for PMCs. Chapter 4 covers mechanical and thermal properties, including those that are specific to laminated structures such as, inter-laminar shear strength and residual compressive strength following barely-visible surface impact damage. The last chapter covers various areas of applications and methods of materials selection. Mustafa Akay, January 2015

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An introduction to polymer-matrix composites

Acknowledgements

Acknowledgements The book emerges from my work at the Ulster Polytechnic/University of Ulster, where I met and worked with various characters and personalities and I would like to mention Lesley Hawe, the late Archie Holmes, Myrtle Young who epitomise for me the constant kindness, help and support I received from the academic, technical and secretarial staff over the years. The book incorporates material taken from various sources, including my lecture notes, research outcomes of my postgraduate students, some of them have become friends for life, and some excellent text books, research papers/news, industry/company/organisation literature and web material that we are so fortunate to have access to. The sources of the materials used are gratefully acknowledged and are listed as references, however, over the years material permeates into teaching notes that is not always possible to trace the references for. I apologise, therefore, for any such material that has no accompanying reference and I express my thanks and gratitude to the people concerned. A special thank you goes to my wife for her proof reading, for the offers of regular walks to blow away the cobwebs and visits to “Waterstones” for coffee and book browsing.

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An introduction to polymer-matrix composites

Introduction

1 Introduction 1.1

Case for composites

Polymers, which are a source of a wide variety of low-priced raw materials, offer many advantages. These include low specific weight, enhanced stability against corrosion, improved electrical and thermal insulation, ease of shaping and economic mass production, and attractive optical properties, e.g. fibre optics, glazing applications, etc. However, they suffer from some serious shortcomings: • exhibiting, quite often, poor mechanical stiffness and strength, and poor resistance against heat • being sensitive to aging i.e. change of the physical, chemical and mechanical properties by light, heat, oxygen and moisture • being combustible • exhibiting large values of coefficient of thermal expansion, which can generate high levels of internal frozen-in stresses. Table 1.1 provides guidance concerning limited resistance of polymers to heat. The polymer abbreviations are defined in Table 1.2. Polymers Semi-crystalline

Amorphous

Long-term working temperature,°C

PEEK, PPS, PTFE, LCP

PES, PSU, PEI, EP

150–250

PET, PBT, POM, PA 66, PA46, PP

PC, UP

90–120

HDPE, LDPE, LLDPE

PS, HIPS, PVC, PMMA, ABS, SAN

< 90

Table 1.1 Long-term temperature limit for some polymers

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An introduction to polymer-matrix composites

Introduction

ABS

acrylonitrile-butadiene-styrene

EP

epoxy resin

HDPE

high-density polyethylene

HIPS

high-impact polystyrene

LCP

liquid crystalline polymer

LDPE

low-density polyethylene

LLDPE

linear low-density polyethylene

PA 46

polyamide 46

PA 66

polyamide 66

PMIA

poly (m-phenylene isophthalamide)

PBT

polybutylene terephthalate

PC

polycarbonate

PEEK

polyetherether ketone

PI

Polyimide (e.g. “Kapton”, “Vespel”)

PI

Thermosetting polyimide

BMI

bismaleimide

PAI

Polyamide imide (e.g.“Torlon”)

PEI

polyetherimide

PES

polyethersulphone

PET

polyethylene terephthalate

PAR

polyarylate

PMMA

polymethyl methacrylate

POM

polyoxymethylene (acetal)

PP

polypropylene

PPO

Polyphenylene oxide and/or poly (2,6-dimethyl-1,4-phenylene oxide)

PPS

polyphenylene sulphide

PS

polystyrene

PSU

polysulphone

PPSS

polyphenylene sulfide sulfone

PTFE

polytetrafluoroethylene

PVC

polyvinyl chloride

SAN

styrene-acrylonitrile

UP

polyester (unsaturated) resin

Table 1.2 Abbrevations used in Table 1.1 and Table 1.6

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An introduction to polymer-matrix composites

Introduction

Some of the shortcomings of polymers as engineering materials, particularly poor strength and stiffness, can be improved by combining them with other materials to form composites. Composite materials are defined as a mixture of two or more relatively homogeneous materials which have been bonded together to produce a material with properties that are superior to the ones exhibited by the individual component materials. This synergistic outcome, obviously, is the driving force for the development of composites. Hull (1981, p. 3) outlines that in fibre reinforced plastics, fibres and plastics with some excellent physical and mechanical properties, are combined to give a material with new and superior properties. Fibres have very high strength and elastic modulus but this is only developed in very fine fibres, with diameter in the range 7–15 µm, and they are usually very brittle. Plastics may be ductile or brittle but they usually have considerable resistance to chemical environments. By combining fibres and resin a bulk material is produced with strength and stiffness close to that of the fibres and with the chemical resistance of plastic. In addition, it is possible to achieve some resistance to crack propagation and an ability to absorb energy during deformation.

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An introduction to polymer-matrix composites

Introduction

Therefore, compared with conventional materials, composites offer: • lightweight • high specific strength and stiffness • high toughness (impact strength) • damping ability (attenuates noise and vibrations/shocks) • high fatigue resistance (improves fatigue life) • corrosion resistance • low and controllable coefficient of thermal expansion (CTE) (i.e. good dimensional stability) • ablative shielding • non or low conductivity • thermal insulation • visual attractiveness • reduced machining • part consolidation: allows reduced number of assemblies and fasteners • ability to manufacture complex shapes and one offs from low cost tooling • damaged structures can be easily repaired • potential to tailor mechanical and thermal properties, particularly by suitable fibre orientation/ arrangement.

1.2

History of the development of composites

The history of composites is covered in various sources, including Strong (2006) and Palucka & BernadetteVincent (2002). Composites date back to the 1500 BC when early Egyptians and Mesopotamian settlers used a mixture of mud and straw to create strong and durable buildings. Straw provided reinforcement to ancient composite products including pottery and boats. The subsequent recorded use of natural fibres include paper making. The first ‘paper’ was invented in ancient China sometime around 200 BC. However, the forerunner of modern paper was also first made in China from rags and plant fibres in 105 AD. The development of paper increasingly made it into a composite material. First, the Chinese used starch as a size for paper as early as 768 to reduce surface porosity an...