Plastics Engineering 3E Episode 1 pps

Contents Preface to the Third Edition Preface to the Second Edition Preface to the First Edition Chapter 1 - General Properties of Plastics... vi Contents Chapter 2 - Mechanical Behav

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PLASTICS ENGINEERING

PLASTICS ENGINEERING

Third Edition

R.J Crawford, BSc, PhD, DSc, FEng, FIMechE, FIM

Department of Mechanical, Aeronautical and Manufacturing Engineering The Queen’s University of Belfast

OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS

SAN DlEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

Butterworth-Heinemann

An imprint of Elsevier Science

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Contents

Preface to the Third Edition

Preface to the Second Edition

Preface to the First Edition

Chapter 1 - General Properties of Plastics

vi Contents

Chapter 2 - Mechanical Behaviour of Plastics 41

2.1 Introduction

2.2 Viscoelastic Behaviour of Plastics

2.3 Short-Term Testing of Plastics

2.4 Long-Term Testing of Plastics

2.5

2.6 Thermal Stresses and Strains

2.7 Multi-layer Mouldings

2.8 Design of Snap Fits

2.9 Design of Ribbed Sections

2.10 Stiffening Mechanisms in Other Moulding Situations

2.1 1 Mathematical Models of Viscoelastic Behaviour

2.15 Fracture Behaviour of Unreinforced Plastics

2.16 The Concept of Stress Concentration

2.17 Energy Approach to Fracture

2.18 Stress Intensity Factor Approach to Fracture

2.19 General Fracture Behaviour of Plastics

2.20 Creep Failure of Plastics

2.20.1

2.20.2 Crazing in Plastics

2.21.1 Effect of Cyclic Frequency

2.21.2 Effect of Waveform

2.21.3 Effect of Testing Control Mode

2.2 1.4 Effect of Mean Stress

2.21.5 Effect of Stress System

2.21.6 Fracture Mechanics Approach to Fatigue

2.22 Impact Behaviour of Plastics

2.22.1 Effect of Stress Concentrations

2.22.2 Effect of Temperature

2.22.3 Miscellaneous Factors Affecting Impact

2.22.4 Impact Test Methods

2.22.5 Fracture Mechanics Approach to Impact

Fracture Mechanics Approach to Creep Fracture

Forms of Fibre Reinforcement in Composites

Analysis of Continuous Fibre Composites

Deformation Behaviour of a Single Ply or Lamina

Summary of Approach to Analysis of Unidirectional

Composites

General Deformation Behaviour of a Single Ply

Deformation Behaviour of Laminates

Summary of Steps to Predict Stiffness of Symmetric

Laminates

General Deformation Behaviour of Laminates

Analysis of Multi-layer Isotropic Materials

Analysis of Non-symmetric Laminates

Analysis of Short Fibre Composites

Creep Behaviour of Fibre Reinforced Plastics

Strength of Fibre Composites

3.16.1 Strength of Single Plies

3.16.2 Strength of Laminates

3.17 Fatigue Behaviour of Reinforced Plastics

3.18 Impact Behaviour of Reinforced Plastics

Chapter 4 - Processing of Plastics

4.3.8 Reaction Injection Moulding

General Features of Single Screw Extrusion

Analysis of Flow in Extruder

General Features of Twin Screw Extruders

Processing Methods Based on the Extruder

Shear Controlled Orientation in Injection Moulding

4.3.9 Injection Blow Moulding

4.3.10 Injection Moulding of Thermosetting Materials

4.9 Processing Reinforced Thermoplastics

4.10 Processing Reinforced Thermosets

4.10.1 Manual Processing Methods

4.10.2 Semi-Automatic Processing Methods

5.8 Residence and Relaxation Times

5.9 Temperature Rise in Die

5.10 Experimental Methods Used to Obtain Flow Data

5.11 Analysis of Flow in Some Processing Operations

5.12 Analysis of Heat 'lkansfer during Polymer Processing

5.13 Calculation of Clamping force

General Behaviour of Polymer Melts

Isothermal Flow in Channels: Newtonian Fluids

Rheological Models for Polymer Melt Flow

Isothermal Flow in Channels: Non-Newtonian Fluids

Isothermal Flow in Non-Uniform Channels

Elastic Behaviour of Polymer Melts

Appendix A - Structure of Plastics

A.l Structure of Long Molecules

A.2

A.3 Arrangement of Molecular Chains

Conformation of the Molecular Chain

Appendix B - Solution of Differential Equations

Appendix C - Stredstrain Relationships

Contents ix Appendix E - Introduction to Matrix Algebra

E.1 Matrix definitions

E.2 Matrix multiplication

E.3 Matrix addition and subtraction

E.4 Inversion of a matrix

E.5 Symmetric matrix

Appendix F - Abbreviations for some Common Polymers

Preface to the Third Edition

Plastics continue to be exciting materials to use and a dynamic area in which to work Every year new application areas are being developed to utilise more fully the unique properties of this class of materials In addition, new processing tech- nologies are emerging to exploit the versatility of plastics and to take advantage

of their ease of manufacture into all types of end products It is very important that students and those already working in the industry are kept fully informed about these new developments In this new edition an attempt has been made

to bring existing subject material up to date and many new sections have been added to cover the innovations introduced over the past decade The number of Worked Examples has been increased and there are many more Set Questions

at the end of each Chapter As in the previous editions, a full set of solutions

to the Set Questions is provided at the end of the book

In this new edition, some re-structuring of the content has taken place The subject material on Fracture that previously formed Chapter 3 has been brought forward to Chapter 2 This chapter now provides a more unified approach to the deformation and fracture behaviour of non-reinforced plastics Chapter 3

is new and deals with all aspects of the mechanical behaviour of composites

in much more detail than the previous editions Composites are an extremely important class of material for modem design engineers and they must form

an integral part of undergraduate and postgraduate teaching There are many

excellent textbooks devoted to this subject but it was felt that an introduction to the analysis of laminates would be a valuable addition to this text It is hoped that the many worked examples in this new chapter will help the student, and the practising engineer, to gain a better understanding of this apparently complex subject area Chapters 4 and 5 are essentially as before but they have been

extensively updated A more unified approach to the analysis of processing has

also been adopted

xii Preface to the Third Edition

As other authors will know, the preparation of a textbook is a demanding, challenging and time-consuming occupation I have been very fortunate to receive many encouraging comments on the previous editions and this has given me the enthusiasm to continue developing the subject material in the book I am very grateful to all of those who have taken the trouble to contact

me in the past and I continue to welcome comments and advice as to how the book could be improved in the future

R.J Crawford September 1997

Preface to the Second Edition

In this book no prior knowledge of plastics is assumed The text introduces the reader to plastics as engineering materials and leads on to the design procedures which are currently in use Since the publication of the first edition the subject has developed in some areas, particularly processing and so this second edition contains the new and up-to-date information Other modifications have also been made to improve the presentation of the contents In particular, Chapter

1 has been completely re-written as an introduction to the general behaviour characteristics of plastics The introduction to the structure of plastics which formed the basis of Chapter 1 in the first edition has been condensed into an

Appendix in the new edition Chapter 2 deals with the deformation behaviour

of plastics It has been expanded from the first edition to include additional

analysis on intermittent loading and fibre composites Chapter 3 deals with the

fracture behaviour of plastics and here the importance of fracture mechanics has been given greater emphasis

Chapter 4 describes in general terms the processing methods which can be used for plastics All the recent developments in this area have been included and wherever possible the quantitative aspects are stressed In most cases a simple Newtonian model of each of the processes is developed so that the approach taken to the analysis of plastics processing is not concealed by math- ematical complexity

Chapter 5 deals with the aspects of the flow behaviour of polymer melts which are relevant to the processing methods The models are developed for both Newtonian and Non-Newtonian (Power Law) fluids so that the results can

xiv Preface to the Second Edition encouraged to develop the subject beyond the level covered in the text To

assist the reader a full set of solutions to the problems is provided at the back

of the book

R.J Crawford January 1987

Preface to the First Edition

This book presents in a single volume the basic essentials of the properties and processing behaviour of plastics The approach taken and terminology used has been deliberately chosen to conform with the conventional engineering approach to the properties and behaviour of materials It was considered that

a book on the engineering aspects of plastics was necessary because there is currently a drive to attract engineers into the plastics industry and although engineers and designers are turning with more confidence to plastics there is still an underlying fear that plastics are difficult materials to work with Their performance characteristics fall off as temperature increases and they are brittle

at low temperatures Their mechanical properties are time dependent and in the molten state they are non-Newtonian fluids All this presents a gloomy picture and unfortunately most texts tend to analyse plastics using a level of chemistry and mathematical complexity which is beyond most engineers and designers The purpose of this text is to remove some of the fears, by dealing with plastics in much the same way as traditional materials The major part of this

is to illustrate how quantitative design of plastic components can be carried out using simple techniques and how apparently complex moulding operations can be analysed without difficulty

Many of the techniques illustrated have been deliberately simplified and so they will only give approximate solutions but generally the degree of accuracy can be estimated and for most practical purposes it will probably be acceptable Once the engineeddesigner has realised that there are proven design procedures for plastics which are not beyond their capabilities then these materials will be more readily accepted for consideration alongside established materials such

as woods and metals On these terms plastics can expect to be used in many new applications because their potential is limited only by the ingenuity of the user

xvi Preface to the First Edition This book is intended primarily for students in the various fields of engi- neering but it is felt that students in other disciplines will welcome and benefit from the engineering approach Since the book has been written as a general introduction to the quantitative aspects of the properties and processing of plas- tics, the depth of coverage is not as great as may be found in other texts on the physics, chemistry and stress analysis of viscoelastic materials this has been done deliberately because it is felt that once the material described here has been studied and understood the reader will be in a better position to decide

if he requires the more detailed viscoelastic analysis provided by the advanced texts

In this book no prior knowledge of plastics is assumed Chapter 1 provides

a brief introduction to the structure of plastics and it provides an insight to

the way in which their unique structure affects their performance There is a resume of the main types of plastics which are available Chapter 2 deals with the mechanical properties of unreinforced and reinforced plastics under the general heading of deformation The time dependent behaviour of the materials

is introduced and simple design procedures are illustrated Chapter 3 continues the discussion on properties but concentrates on fracture as caused by creep, fatigue and impact The concepts of fracture mechanics are also introduced for reinforced and unreinforced plastics

Chapter 4 describes in general terms the processing methods which can be used for plastics and wherever possible the quantitative aspects are stressed

In most cases a simple Newtonian model of each of the processes is devel- oped so that the approach taken to the analysis of plastics processing is not

concealed by mathematical complexity Chapter 5 deals with the aspects of the

flow behaviour of polymer melts which are relevant to the processing methods The models are developed for both Newtonian and Non-Newtonian (Power Law) fluids so that the results can be directly compared

Throughout the book there are worked examples to illustrate the use of the theory and at the end of each chapter there are problems to be solved by the reader These are seen as an important part of the book because in solving the problems the reader is encouraged to develop the subject material beyond the level covered in the text Answers are given for all the questions

R.J Crawford

CHAPTER 1 - General Properties of Plastics

of metals This is an important point because just as it is accepted that zinc has quite different properties from steel, similarly nylon has quite different properties from ITFE Few designers would simply specify metal as the mate- rial for a particular component so it would be equally unsatisfactory just to recommend plastic This analogy can be taken still further because in the same way that there are different grades of steel there are also different grades of,

say, polypropylene In both cases the good designer will recognise this and select the most appropriate material and grade on the basis of processability, toughness, chemical resistance, etc

It is usual to think that plastics are a relatively recent development but in

fact, as part of the larger family called polymers, they are a basic ingredient of

animal and plant life Polymers are different from metals in the sense that their structure consists of very long chain-like molecules Namal materials such as

silk, shellac, bitumen, rubber and cellulose have this type of structure However,

it was not until the 19th century that attempts were made to develop a synthetic

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