Fatigue and Fracture of Fibre Metal Laminates (eBook)

Preface 6
Contents 8
1 Introduction 14
Abstract 14
1.1 Introduction 14
1.2 Development Perspectives 15
1.2.1 Increased Damage Growth Resistance of Metal Laminates 15
1.2.2 Utilization in Context of Damage Tolerance 16
1.2.3 Increasing Strength of Composites 17
1.3 From Material Towards Structural Application 18
1.4 Contribution to the FML Knowledge 18
References 18
2 Laminate Concepts & Mechanical Properties
Abstract 20
2.1 Introduction 20
2.2 Aluminium with Epoxy-Based Adhesive Systems 21
2.2.1 ARALL and GLARE, Codes and Standardisation 22
2.2.2 Aramid Fibres (ARALL) 24
2.2.3 Glass Fibres (GLARE, Central) 27
2.2.4 Carbon Fibres (CARE/CARALL) 30
2.2.5 Polymer Fibres (HP-PE, Zylon) 31
2.2.6 M5 Fibres 33
2.3 Other Metal Constituents 34
2.3.1 Titanium-Based FMLs 34
2.3.2 Stainless Steel-Based FMLs 35
2.3.3 Magnesium-Based FMLs 35
2.4 Thermoplastic Adhesive Systems 36
2.5 Innovative Hybridization Concepts 36
References 38
3 Patents and Intellectual Property 41
Abstract 41
3.1 Introduction 41
3.2 Material Concept Development 41
3.2.1 Improving Fatigue and Crack Growth 41
3.2.2 Improving Impact Resistance and Tolerance 44
3.2.3 Thickness Steps 45
3.2.4 Thick Panel Concepts for Lower Wing Covers 47
3.2.5 Alternative Fuselage Skin Concepts 49
3.3 Splicing Concepts 51
3.4 Manufacturing Aspects 53
3.4.1 Post-stretching Panels After Curing 53
3.4.2 Pre-stretching Panels During Curing 54
3.4.3 Lay-up and Curing Concepts 55
3.4.4 Alternative Impregnation Processes 57
3.5 Design of Fuselage Panels 58
3.5.1 General Fuselage Panel Concepts 58
3.5.2 Interlaminar Reinforcements and Inserts 59
3.5.3 Special Design Features 61
3.6 Design of Panel Stiffening Elements 61
3.7 FML Components 63
3.8 Discussion 64
3.8.1 Flat Material Concepts 64
3.8.2 Design Aspects 67
3.9 Concluding Remarks 67
References 68
4 Stress and Strain 71
Abstract 71
4.1 Introduction 71
4.2 Stress–Strain in Orthotropic Materials Under Plane Stress 71
4.3 Classical Laminated Plate Theory 73
4.4 Residual Stresses 73
4.5 Failure of the Composite Constituent 76
4.6 Plasticity of the Metal Constituent 77
4.7 Generalized Theories of Plasticity 78
4.8 Post-stretching 79
4.9 Shear Stress and Strain 82
4.10 Out-of-Plane (Bending and Torsion) 83
4.11 Simple Methods for Design Purposes 84
4.11.1 Metal Volume Fraction 84
4.11.2 Determination of Shear Properties Using Uniaxial Material Data 85
4.12 Limit of Validity of CLT and MVF 87
References 87
5 Blunt Notch Strength 89
Abstract 89
5.1 Introduction 89
5.2 Definitions and Failure Phenomena 91
5.2.1 Definitions 91
5.2.2 Notch Sensitivity and Ductility 92
5.2.3 Biaxial Loading Using Uniaxial Data 94
5.2.4 Composite Failure Modes 95
5.2.5 Plasticity-Induced Delamination 97
5.2.6 Other Failure Phenomena 98
5.2.7 Blunt Notch Strength and Ultimate Strength 99
5.3 Theoretical Approaches 100
5.3.1 Tsai–Hill/Norris Failure Criteria 100
5.3.2 Point and Average Stress Criteria 101
5.3.3 Blunt Notch Factor to Ultimate Strength in Net Section 103
5.4 Applicability to General Loading Conditions 104
5.4.1 Uniaxial Off-Axis Loading 104
5.4.2 Shear Loading 106
5.4.3 Biaxial Loading 107
5.5 Simple Methods for Design Purposes 108
5.5.1 Metal Volume Fraction 108
5.5.2 Neuber’s Postulate 109
References 111
6 Bearing Strength 113
Abstract 113
6.1 Introduction 113
6.2 Definition of Bearing Strength 114
6.3 Failure Phenomena 115
6.3.1 Delamination Buckling 115
6.3.2 Bearing Failure 117
6.4 Diameter-to-Thickness Ratio 119
6.5 Influence of the Diameter-to-Width Ratio 120
6.6 Influence of Edge Distance 121
6.7 In-Axis Versus Off-Axis Loading 122
6.8 Analysis and Prediction Methods 125
6.8.1 Bilinear Constituent Representation with Rules of Mixtures 125
6.8.2 Simplified MVF Method 130
6.8.3 Finite Element Analyses 131
6.9 Additional Studies 132
6.9.1 Bearing/ByPass Diagrams 132
6.9.2 Environmental Exposure 135
References 135
7 Fatigue Initiation 138
Abstract 138
7.1 Introduction 138
7.2 Definition of Initiation 138
7.3 Definition of Stresses 142
7.4 Stress Concentration in a Uniaxial Stress Field 143
7.5 Peak Stresses at Locations Other Than ? = ±90° 145
7.6 Stress Concentration in a Biaxial Stress Field 147
7.7 Other Load Cases 148
7.8 Fatigue Stresses at the Notch Root 148
7.9 Fatigue Initiation Life Estimation 150
7.10 Adapting Reference Data for Sm and Kt 150
7.11 Accuracy of Predictions 152
7.12 Size Effects 153
7.13 Constant Versus Variable Amplitude Loading 153
7.14 Mechanically Fastened Joints 155
7.15 Influence of Post-stretching 156
References 157
8 Static and Fatigue Delamination 158
Abstract 158
8.1 Introduction 158
8.2 Strain Energy Release Rate 159
8.3 Interface Geometry 161
8.3.1 Resin-Rich Layers 161
8.3.2 Tapes Versus Weaves 165
8.4 Modes I, II and Mixed Mode 166
8.4.1 Mode I 166
8.4.2 Mode II 166
8.4.3 Mixed Mode 169
8.5 Constant Versus Variable Amplitude Loading 171
8.5.1 Macroscopic Observations 171
8.5.2 Microscopic Observations 173
8.6 Asymptotes in Delamination Characteristics 176
8.6.1 Static Delamination Growth 176
8.6.2 Delamination Threshold 178
8.7 Delamination Buckling 179
8.8 Effect of Post-stretching 180
References 182
9 Fatigue Crack Propagation 185
Abstract 185
9.1 Introduction 185
9.2 Crack Geometries 186
9.3 Fatigue Crack Growth Characteristics 187
9.4 Superposition of Far-Field Stresses and Fibre Bridging 190
9.5 Delamination Shapes 194
9.6 Metal Layer Crack Growth Resistance 196
9.7 Finite Width Correction Factors 199
9.8 Other Correction Factors 200
9.8.1 Open Hole and Pin-Loaded Hole 203
9.8.2 Edge Cracks Versus Central Cracks 205
9.9 Fatigue Threshold 206
9.10 Surface Cracks 208
9.11 Part-Through Cracks 211
9.12 In-Axis Versus off-Axis Loading 213
9.13 Crack Path Angles and Path Deflections 218
9.14 Constant Versus Variable Amplitude Loading 221
9.15 Post-stretching 223
9.16 Biaxial Fatigue 224
References 227
10 Residual Strength 231
Abstract 231
10.1 Introduction 231
10.2 Through-Cut Cracks 233
10.2.1 Fracture Mechanisms 235
10.2.2 KR-Curve or R-Curve Concept 236
10.2.3 Compliance Calibration for Orthotropic FML Panels 239
10.2.4 Crack Tip Opening Angle or CTOA Concept 241
10.2.5 Superposition Principles for Crack Opening 244
10.2.6 In-Axis Versus Off-Axis Loading 246
10.3 Fatigue Through Crack 247
10.3.1 Observations 247
10.3.2 Prediction Methodology 250
10.4 Part-Through Cracks 251
10.5 Surface Cracks 254
10.6 Impact Damage Tolerance 256
References 259
11 Effect of Temperature 263
Abstract 263
11.1 Introduction 263
11.2 Temperature-Induced Residual Stresses 263
11.3 Thermal Properties of FMLs 264
11.3.1 Thermal Conductivity 264
11.3.2 Specific Heat 267
11.4 Fatigue Initiation 267
11.4.1 Temperature Effect on Mechanical Properties 268
11.4.2 Temperature Effect on Fatigue Properties 269
11.5 Fatigue Damage Growth 272
11.5.1 Temperature and Fatigue Crack Growth Resistance of Metals 272
11.5.2 Temperature and Fatigue Delamination Resistance 273
11.5.3 Influence of Temperature on Damage Growth in FMLs 276
11.6 Thermal Fatigue 277
References 278
12 Effect of Environment 281
Abstract 281
12.1 Introduction 281
12.2 Moisture Absorption 282
12.2.1 Planar Diffusion of Moisture 282
12.2.2 Relevance of Exposure Type 285
12.3 Effects of Moisture Ingress 287
12.3.1 Static Strength 287
12.3.2 Blunt Notch Strength 288
12.3.3 Delamination Resistance 291
12.3.4 Fatigue Crack Growth 293
12.3.5 Residual Strength 294
12.4 Effect of Frequency 297
References 299
13 Acoustic Fatigue 301
Abstract 301
13.1 Introduction 301
13.2 Damping Characteristics 302
13.3 Acoustic Fatigue 303
13.4 High-Frequency Bending Fatigue Experiments 303
13.4.1 Specimen Configuration and Test Set-up 303
13.4.2 Test Procedure 304
13.4.3 Performed Tests 305
13.5 Results and Observations 306
13.6 Concluding Remarks 308
References 308
Index 309