ENGINEERING COMPOSITE MATERIALS Bryan Harris The Institute of Materials, London 1999 CONTENTS 1 THE NATURE OF COMPOSITE MATERIALS....................................................................... 5 1.1 WHAT ARE COMPOSITES? ..............................................................................................................................5 1.2 CONVENTIONAL MATERIALS AND THEIR LIMITATIONS ..................................................................................6 1.3 STRONG FIBRES..............................................................................................................................................7 1.3.1 Glass fibres..........................................................................................................................................8 1.3.2 Carbon fibres.......................................................................................................................................8 1.3.3 Silicon carbide.....................................................................................................................................9 1.3.4 Alumina and alumina/silica compounds............................................................................................10 1.3.5 Organic Fibres ..................................................................................................................................10 1.3.6 Styles of reinforcement ......................................................................................................................11 1.4 THE SCOPE FOR REINFORCEMENT OF CONVENTIONAL MATERIALS................................................................12 1.4.1 Functions of the matrix......................................................................................................................12 1.4.2 Metals ................................................................................................................................................13 1.4.3 Polymeric materials...........................................................................................................................13 1.4.4 Glasses, ceramics and cement ...........................................................................................................14 1.4.5 Carbon...............................................................................................................................................15 1.5 REFERENCES TO CHAPTER 1 .........................................................................................................................15 1.5.1 General bibliography ........................................................................................................................16 1.5.2 Sources of data ..................................................................................................................................17 2 MAKING COMPOSITE MATERIALS .................................................................................... 18 2.1 THE COMBINING OF MATERIALS ...................................................................................................................18 2.2 THE INTERFACE ...........................................................................................................................................19 2.3 MANUFACTURING PROCESSES......................................................................................................................20 2.3.1 Polymer-matrix composites ...............................................................................................................20 2.3.2 Metal-matrix composites ...................................................................................................................22 2.3.3 Ceramic-matrix composites...............................................................................................................23 2.3.4 Hybrid composites .............................................................................................................................24 2.4 DEFECTS IN MANUFACTURED POLYMERIC COMPOSITES ...............................................................................25 2.5 METHODS OF NON-DESTRUCTIVE EVALUATION FOR POLYMER COMPOSITES.................................................28 2.5.1 Optical inspection..............................................................................................................................28 2.5.2 Radiographic methods.......................................................................................................................28 2.5.3 Thermal imaging................................................................................................................................28 2.5.4 Ultrasonic techniques ........................................................................................................................29 2.5.5 Optical fibre sensors..........................................................................................................................29 2.5.6 Microwave methods...........................................................................................................................30 2.5.7 Dynamic mechanical analysis. ..........................................................................................................30 2.5.8 Acoustic emission methods. ...............................................................................................................31 2.6 THE USE OF COMPOSITES..............................................................................................................................31 2.7 REFERENCES TO CHAPTER 2 .........................................................................................................................31 3 ELASTIC PROPERTIES OF FIBRE COMPOSITES............................................................. 33 3.1 SIMPLE MICROMECHANICAL MODELS...........................................................................................................33 3.2 THE HALPIN-TSAI EQUATIONS .....................................................................................................................36 3.3 THE COMPRESSION MODULUS.......................................................................................................................38 3.4 THE ANISOTROPIC PROPERTIES OF A THIN LAMINA .......................................................................................39 3.5 ORIENTATION-DEPENDENCE OF THE ELASTIC PROPERTIES OF A UNIDIRECTIONAL LAMINA...........................42 3.6 MULTI-PLY LAMINATES................................................................................................................................44 3.7 SHORT-FIBRE COMPOSITES ...........................................................................................................................48 3.8 HYBRID COMPOSITES ...................................................................................................................................51 3.9 RESIDUAL STRAINS ......................................................................................................................................54 3.10 TEXTILE COMPOSITES..............................................................................................................................56 3.11 PLIANT COMPOSITES................................................................................................................................58 3.12 REFERENCES TO CHAPTER 3 ....................................................................................................................59 4 THE STRENGTH OF FIBRE COMPOSITES................................................................................ 61 4.1 TENSILE STRENGTH ......................................................................................................................................61 4.1.1 Unidirectional continuous-fibre composites......................................................................................61 4.1.2 The problem of the strength of brittle fibres......................................................................................63 4.1.3 Progressive damage and failure in unidirectional composites..........................................................65 4.1.4 Calculation of the tensile strength of a unidirectional composite .....................................................67 4.1.5 Transverse strength ...........................................................................................................................69 4.1.6 Orientation-dependence of composite strength .................................................................................71 4.1.7 The strengths of multi-ply laminates..................................................................................................72 4.1.8 Short-fibre composites.......................................................................................................................75 4.1.9 Hybrid composites .............................................................................................................................79 4.2 COMPRESSION STRENGTH.............................................................................................................................80 4.2.1 Compression strength after impact....................................................................................................84 4.3 SHEAR STRENGTH ........................................................................................................................................85