Environmental degradation in industrial composites

CONTENTS List of Figures xi List of Tables xix List of Case Studies xxi Acknowledgements xxiii 1 Introduction 1 1.1 Introductory Case Study: Windmill Blades 1 1.2 Introduction to Environmental Degradation in Composite Materials 5 1.3 Composite Materials: General Definitions 6 1.3.1 Classification 7 1.3.1.1 Classification by polymer type 7 1.3.1.2 Classification by reinforcement type and geometry 7 1.3.2 Manufacturing 8 1.3.3 Technical Specificities of Composite Materials 10 1.3.3.1 Inhomogeneity and anisotropy 10 1.3.3.2 Non-linearity 11 1.3.3.3 Environmental dependence 12 1.4 Advanced Composite Market 12 References 15 2 Effect of Temperature on Polymer Matrix Composites 17 2.1 Introduction 17 2.2 Polymer Matrix Composites versus Metals 21 2.2.1 Stress-Strain Curves 21 2.2.2 Ductility versus Brittleness 22 2.2.3 Viscoelasticity - Definition 23 2.3 Modeling Creep, Relaxation and Time-dependent Response to Cyclic Loads in Polymers and Composites 25 2.3.1 Creep versus Stress Relaxation 25 2.3.2 Models for Creep and Stress Relaxation: Introduction to Viscoelasticity 25 CONTENTS 2.3.2.1 Creep 27 2.3.2.2 Relaxation 28 2.3.2.3 Dynamical loading 28 23.2A Dynamic versus static moduli 30 2.3.2.5 Important consequences on composites 31 2.4 Transitions and Key Temperatures 32 2.4.1 The Four Regions of the Master Curve 32 2.4.1.1 Glassy stage 33 2.4.1.2 Glass transition region 35 2.4.1.3 Rubbery stage 36 2.4.1.4 Rubbery flow 38 2.4.1.5 Instantaneous versus time-dependent stiffness 38 2.4.2 Transition Temperatures 40 2.4.2.1 Glass transition temperature 41 2.4.2.2 Secondary transition temperatures 44 2.4.2.3 Melting temperature 44 2.4.2.4 Gelation temperature 46 2.4.2.5 Degradation temperature 47 2.4.2.6 Other engineering temperatures 48 2.4.3 High Temperature Polymers 48 2.5 Time-Temperature Equivalence 50 2.5.1 Time-Temperature Superposition 50 2.5.2 WLF Model and Limits 51 2.5.3 Physical Aging 51 2.5.4 Accelerated Testing 52 2.6 Further Temperature Effects on Composite Properties 55 2.6.1 Strength and Other Properties 55 2.6.2 Composites, Time and Temperature - Common Pitfalls and General Precautionary Rules 61 2.7 Composite Exposure to Extreme Temperatures 63 2.8 Testing 73 2.8.1 Dilatometry Methods 73 2.8.2 Thermal Methods 73 2.8.2.1 Differential thermal analysis (DTA) 73 2.8.2.2 Differential scanning calorimetry 74 2.8.3 Mechanical Methods 75 2.8.4 Electric and Magnetic Methods 76 2.8.4.1 Conduction: Direct current (DC) 76 2.8.4.2 Conduction: Alternating current (AC) 77 2.8.5 Standard Test Methods 77 2.9 Tool Kit 79 References 80 CONTENTS Liquids and Gas Exposure 85 3.1 Introduction 85 3.2 The Diffusion Phenomenon 87 3.2.1 Fickian Diffusion 88 3.2.2 Practical Implications of Pick's Laws 89 3.2.3 Gas Permeation 96 3.3 Liquid and Gaseous Environment Effects on the Matrix 102 3.3.1 Influence of Water Absorption on Transition Temperatures in Polymers 102 3.3.2 Polymer SwelHng 103 3.3.3 Changes in the Thermo-mechanical Properties 105 3.3.4 Limits of the Model 105 3.4 Liquid and Gaseous Environment Effects on the Fibers 107 3.5 Liquid and Gaseous Environment Effects on the Composite 110 3.5.1 Diffusion in Composites 111 3.5.2 Effects of Exposure on Composite Properties 112 3.5.2.1 Changes in transition temperatures 113 3.5.2.2 Changes in mechanical response 113 3.5.2.3 Changes in the failure mechanisms 116 3.6 Freeze Thaw 123 3.7 Cavitation Erosion 127 3.8 Testing 129 3.9 Tool Kit 132 References 133 Effects of Electrical Fields and Radiations on Polymer Matrix Composites 137 4.1 Introduction 137 4.2 Effects of Electrical Field on Polymer Matrix Composites 138 4.2.1 Introduction to Insulation Materials 138 4.2.1.1 Type of applications 138 4.2.1.2 Most common materials 140 4.2.2 Definition of Electrical Quantities and Properties 142 4.2.2.1 Capacitance, resistivity, conductivity, polarization 143 4.2.2.2 Losses 145 4.2.2.3 Specificity of composites 150 4.2.2.4 Practical consequences 152 4.2.3 Breakdown and Failure 155 4.2.3.1 Electrical breakdown 155 4.2.3.2 Physical degradation and failure (e.g. cycling) 157 4.2.4 Special Focus: Thermal Cycling of Generator Bars 161 4.3 Radiations 166 4.3.1 The Different Types of Radiations and General Effects 166 4.3.2 Ultra-violet (UV) Radiations 167 CONTENTS 4.3.3 Electron-beam Radiations 167 4.3.4 Nuclear Radiations 168 4.4 Testing 169 4.4.1 High Voltage Test 169 4.4.2 Life Endurance Test 169 4.4.3 Loss Tangent (tan 8) Measurement 169 4.4.4 Partial Discharge Test 170 4.4.5 Related ASTM Norms 170 4.5 Tool Kit 171 References 172 5 Environmental Impact on Micromechanical and Macromechanical Calculations 175 5.1 Introduction 175 5.2 Environmental Effects on Single Layer Composites: Micromechanics 178 5.2.1 Environmental Impact on Micromechanical Calculations of Stiffness 178 5.2.1.1 Definitions 178 5.2.1.2 Unidirectional composite 180 5.2.1.3 Random reinforcement 185 5.2.2 Environmental Impact on Micromechanical Calculations of Strength 186 5.2.3 Environmental Impact on Micromechanical Calculations of Other Composite Properties 187 5.2.4 Discussion on the Validity of the Approach 189 5.3 Environmental Impact on Stresses and Strains of Composite Structures: Macromechanics 189 5.3.1 Thin Plates - CLT 190 5.3.1.1 Definitions 190 5.3.1.2 Calculation of the laminae macroscopic properties 196 5.3.1.3 Laminate stresses and strains (CLT) 197 5.3.1.4 Thermal and moisture stresses 200 5.3.1.5 Shells 203 5.3.2 Impact of Non-Hnear Viscoelasticity on the Mechanical Properties of Composites 209 5.4 Environmental Impact on the Damage Mechanisms and Failure of Composite Structures 209 5.4.1 Composite Failure 209 5.4.2 Maximum Stress and Maximum Strain Criteria 210 5.4.2.1 Maximum stress criterion 210 5.4.2.2 Maximum strain criterion 210 5.4.2.3 Limit of the criteria 211 CONTENTS ix 5.4.3 Polynomial Criteria 213 5.4.4 Discussion on Recent Failure Criteria 214 5.5 Special Focus: Finite Element Commercial Softwares 215 5.6 Testing 220 5.6.1 Tensile Testing 221 5.6.2 Compression Testing 221 5.6.3 Shear Testing 221 5.6.4 Flexural Testing 221 5.6.5 Interface Testing 222 5.6.6 Fatigue Testing 222 5.6.7 Standardized Tests 222 5.7 Tool kit 224 References 229 Cycling Mechanical and Environmental Loads 233 6.1 Introduction 233 6.2 Environmental and Mechanical Cycling versus Static Loading 237 6.2.1 Definitions 237 6.2.2 Mechanical Fatigue in Composite Materials 241 6.2.2.1 Statistical nature of polymer matrix composite failure under cycling loads 241 6.2.2.2 Factors influencing the fatigue life 243 6.2.2.2.1 Constituents 243 6.2.2.2.2 The composite lay-up and reinforcement geometry 245 6.2.2.2.3 The loading conditions 246 6.2.2.2.4 The environment 247 6.2.2.2.5 The initial state 247 6.2.3 Stress Rupture 248 6.2.4 Environmental Cycling 250 6.2.5 Practical Complexity 252 6.3 Sequential and Combined Loading 257 6.3.1 Approaches 257 6.3.2 Durability Concept 258 6.3.2.1 Critical element 258 6.3.2.2 Failure functions 259 6.3.2.3 Strength as a damage metric 259 6.3.2.4 Practical implications 260 6.3.3 Example 262 6.4 Special Focus - Testing: Design of Experiments for Composites 280 6.4.1 Introduction 280 6.4.2 Selecting the Proper Design 282 CONTENTS 6.4.3 Conducting the Experiments 284 6.4.4 Analyzing the Experiments 285 6.5 Tool Kit 289 References 289 Index 293