Preface	8
	Acknowledgments	10
	Contents	12
	Financial Support	16
	About the Author	18
	Chapter 1: Introduction	19
	References	22
	Chapter 2: Failure of Fiber-Reinforced Composites	23
	2.1 Classification of Failure Mechanisms	24
	2.1.1 Microscale	25
	2.1.2 Mesoscale	31
	2.1.3 Macroscale	34
	2.2 Failure Theories for Fiber-Reinforced Composites	36
	2.2.1 Quasi-Static Failure	36
	2.2.2 Quasi-Static Failure Including Growth of Damage, Damage Mechanics, and Degradation	39
	2.2.3 Long-Term Behavior	46
	2.2.3.1 Creep and Stress Rupture	46
	2.2.3.2 Fatigue	48
	2.2.4 High Velocity	50
	2.3 Challenges in Mechanical Testing of Fiber-Reinforced Materials	51
	2.3.1 Detection of First Failure Onsets	52
	2.3.2 Tracking Failure Evolution	53
	2.3.3 Ductile Matrix Materials	54
	2.4 What Can In Situ Methods Contribute to Mechanical Testing?	54
	2.4.1 In Situ Microscopy	55
	2.4.2 Digital Image Correlation	55
	2.4.3 X-Ray Methods	56
	2.4.4 Thermography	58
	2.4.5 Shearography	59
	2.4.6 Ultrasonic Measurements	60
	2.4.7 Acoustic Emission	61
	2.4.8 Electromagnetic Emission	61
	References	62
	Chapter 3: Digital Image Correlation	74
	3.1 Principle of Operation	75
	3.2 System Accuracy	80
	3.2.1 Error Sources	81
	3.2.1.1 Systematic Errors	81
	3.2.1.2 Random Errors	83
	3.2.1.3 Stereo Vision	84
	3.2.2 Resolution	84
	3.3 Strain Concentration	86
	3.3.1 Measurement of Strain Concentration Due to Internal Defects	88
	3.3.2 FEM Modeling of Strain Concentration Due to Internal Defects	97
	3.3.2.1 Full-Field Comparison	98
	3.3.2.2 Signatures of Artificial Defects	104
	3.3.3 Detectability of Defects Using DIC	114
	3.3.3.1 Experimental Parameters	116
	3.3.3.2 Applicability of the Modeling Approach to Real Defects	120
	3.3.3.3 Limitations Due to System Accuracy	122
	3.4 Application to Composites	128
	3.4.1 DIC as Optical Extensometer	128
	3.4.1.1 Tensile Testing of Unidirectional Fiber Reinforced Polymers	129
	3.4.1.2 Compressive Testing of Unidirectional Fiber Reinforced Polymers	131
	3.4.1.3 V-Notched Rail Shear Testing of Unidirectional Fiber Reinforced Polymers	133
	3.4.2 Detection of Failure Onsets	135
	3.4.2.1 Short-Beam Shear Tests	136
	3.4.2.2 End-Notched Flexure Tests	138
	3.4.3 Detectability of Failure Mechanisms	141
	References	143
	Chapter 4: Acoustic Emission	147
	4.1 Principle of Operation	147
	4.2 Source Mechanics	149
	4.2.1 AE Rise-Times and Plate Waves	151
	4.2.2 AE Source Model Implementation for Fiber Reinforced Materials	154
	4.2.2.1 Source Models for Microscale	159
	4.2.2.2 Source Models for Meso- and Macroscale	162
	4.2.3 Case Studies for Acoustic Emission Sources in Fiber Reinforced Materials	163
	4.2.3.1 Inter-fiber Failure	166
	Tensile Perpendicular	167
	Compression Perpendicular	172
	Shear Parallel	174
	Bending sigman	177
	4.2.3.2 Delamination	181
	Shear Parallel	183
	Bending sigman	185
	4.2.3.3 Fiber Failure	189
	Tension Parallel	189
	Compression Parallel	192
	4.2.3.4 Fiber Bridging	195
	4.2.3.5 Influence of Crack Length	200
	4.2.3.6 Influence of Fracture Surface	201
	4.2.3.7 Influence of Depth Position	202
	4.2.4 Detectability of Failure Mechanisms	203
	4.3 Wave Propagation	208
	4.3.1 Attenuation	218
	4.3.1.1 Geometric Spreading	219
	4.3.1.2 Thermoelastic and Akhiezer Dissipation	219
	4.3.1.3 Dispersion	220
	4.3.1.4 Scattering	220
	4.3.1.5 Dissipation into Adjacent Media	220
	4.3.1.6 Modeling Attenuation	220
	4.3.2 Influence of Geometry	222
	4.3.3 External and Internal Obstacles	230
	4.3.3.1 Reference Case	232
	4.3.3.2 Rivets and Bolts	234
	4.3.3.3 Holes	236
	4.3.3.4 Inter-fiber Cracks	236
	4.3.3.5 Broken Fibers	239
	4.3.3.6 Delamination	240
	4.3.3.7 Influence on Signal Arrival Times	241
	4.4 Detection of Acoustic Emission Signals	242
	4.4.1 Comparison of Sensor Types	246
	4.4.2 Sensor Modeling	249
	4.4.2.1 Influence of Attached Circuit	251
	4.4.2.2 Influence of Sensor Aperture	253
	4.4.2.3 Influence of Impedance Mismatch	254
	4.4.3 Waveguides	255
	4.4.3.1 Shape of Waveguide	258
	4.4.3.2 Diameter of Waveguide	259
	4.4.3.3 Material of Waveguide	259
	4.4.3.4 Influence of Temperature Gradient	261
	4.4.4 Other Factors Affecting Sensor Sensitivity	261
	4.4.4.1 Coupling Medium	261
	4.4.4.2 Sensor Fixation	264
	4.5 Signal Classification	266
	4.5.1 Recommended Practices Before Starting Signal Classification	268
	4.5.2 Pattern Recognition Method to Detect Natural Clusters	272
	4.5.3 Uncertainty of Classification	276
	4.5.4 Factors of Influence	280
	4.5.4.1 Source-Sensor Distance	281
	4.5.4.2 Plate Thickness	284
	4.5.4.3 Stacking Sequence	285
	4.5.4.4 Internal Damage	292
	4.5.4.5 Sensor Type	294
	4.5.4.6 Signal-to-Noise Ratio	297
	4.6 Source Localization	298
	4.6.1 Determination of Signal Onset	301
	4.6.2 Classical Localization Methods	303
	4.6.3 Source Localization Methods Based on Neural Networks	307
	4.6.3.1 Training Stage Using Test Sources	309
	4.6.3.2 Compensation of Acoustic Anisotropy	314
	4.6.3.3 Discontinuous Deltat-Fields	318
	4.6.3.4 Scale Invariance and Portability	319
	4.7 Application to Composites	321
	4.7.1 AE Source Identification Using FEM Results	321
	4.7.2 Detection of Failure Onset	325
	4.7.2.1 Apparent Interlaminar Shear Strength Tests	325
	4.7.2.2 End-Notched Flexure Tests	327
	4.7.2.3 Transverse Crack Tension Tests	328
	4.7.3 Comparison to Failure Criteria Predictions	333
	4.7.3.1 Unidirectional Laminates	333
	4.7.3.2 Cross-Ply Laminates	336
	4.7.4 Tracking Failure Evolution	343
	4.7.4.1 Double-Cantilever Beam Testing	343
	4.7.4.2 Tensile Testing	350
	4.7.4.3 Structural Components	355
	References	365
	Chapter 5: Electromagnetic Emission	376
	5.1 Principle of Operation	376
	5.2 Source Mechanism	378
	5.2.1 Modeling of Electromagnetic Emission Sources	386
	5.2.1.1 Implementation and Validation	387
	5.2.1.2 Source Radiation Pattern	396
	5.2.1.3 Influence of Distance Between Source and Sensor	398
	5.2.1.4 Influence of Electrical Properties	400
	5.2.1.5 Sources in Fiber Reinforced Composites	400
	5.2.2 Test Sources for Electromagnetic Emission	404
	5.3 Signal Propagation	411
	5.4 Detection of Electromagnetic Emission Signals	415
	5.4.1 EME Detector Concepts	416
	5.4.1.1 Capacitance Plate Sensors	418
	5.4.1.2 Wire Sensors	421
	5.4.1.3 Coil Sensors	422
	5.4.1.4 Comparison and Common Aspects	423
	Material	426
	Positioning	426
	Preamplifier	427
	Acquisition	427
	5.4.2 Electromagnetic Shielding	428
	5.4.2.1 Apertures	435
	5.4.2.2 Waveguides Below Cutoff	438
	5.4.2.3 Seams	440
	5.4.2.4 Cable Penetrations	441
	5.5 Application to Composites	442
	5.5.1 Measurement of EME Due to Crack Formation	442
	5.5.1.1 Polymer Failure	443
	5.5.1.2 Fiber Filament Failure	448
	5.5.1.3 Composites	451
	5.5.2 Measurement of Fracture Surface Orientation	460
	5.5.3 Detectability of Failure Mechanisms	465
	5.5.3.1 Absolute System Limits	465
	5.5.3.2 Signal-to-Noise Ratio	466
	5.5.3.3 Acquisition Mode	467
	References	468
	Chapter 6: Computed Tomography	472
	6.1 Principle of Operation	473
	6.2 Detail Visibility	476
	6.2.1 Object Resolution	477
	6.2.2 Artifacts	479
	6.2.2.1 Physics-Based Artifacts	481
	Beam Hardening	481
	Cupping Artifact	481
	Dark Bands	482
	High-Density Foreign Material Artifact	482
	Partial Volume Averaging	483
	Quantum Mottle (Noise)	484
	Photon Starvation	486
	Undersampling	486
	6.2.2.2 Hardware-Based Artifacts	487
	Ring Artifact	487
	Tube Arcing	487
	6.2.2.3 Reconstruction Artifacts	488
	Cone-Beam Effect	488
	Windmill Artifacts	488
	6.2.2.4 Motion Artifacts	489
	6.2.3 Detectability of Defects in Fiber Reinforced Materials	490
	6.3 Volumetric Inspection of Materials	496
	6.3.1 Concepts for Ex Situ Loading	496
	6.3.2 Concepts for In Situ Loading	497
	6.3.2.1 Type of X-ray Source	498
	6.3.2.2 Type of X-ray Detector	499
	6.3.2.3 Type of Load Rig	499
	Tensile or Compressive Load Test	501
	Mode I Test	504
	Flexural Test and Mode II Test	505
	Thermal Loading	506
	Imaging Requirements	507
	6.4 Digital Volume Correlation	508
	6.5 Application to Composites	513
	6.5.1 Ex Situ Testing	517
	6.5.1.1 Visualization of Damage Progress	517
	6.5.1.2 Extraction of Geometries from Volume Data	521
	6.5.2 In Situ Testing	530
	6.5.2.1 Inter-fiber Failure	533
	6.5.2.2 Fiber Failure	535
	6.5.2.3 Interlaminar Failure	540
	References	542
	Chapter 7: Combination of Methods	548
	7.1 Comparison of In Situ Methods	549
	7.1.1 In Situ Capabilities	551
	7.1.2 Detectability of Failure Mechanisms	553
	7.1.3 Detection Sensitivity	555
	7.1.4 Extension of Methods to Large Scale and Field Testing	558
	7.2 Established Method Combinations	563
	7.2.1 Imaging Methods and Acoustic Emission	563
	7.2.2 Digital Image Correlation and Acoustic Emission	570
	7.2.3 Thermography and Acoustic Emission	573
	7.2.4 Computed Tomography and Acoustic Emission	578
	7.2.4.1 Ex Situ Computed Tomography	578
	7.2.4.2 In Situ Computed Tomography	588
	Inter-Fiber Failure	593
	Fiber Failure	602
	7.2.5 Computed Tomography and Digital Image Correlation	605
	7.2.6 Electromagnetic Emission and Acoustic Emission	605
	7.2.7 Acousto-Ultrasonics	611
	7.3 Future Developments	616
	7.3.1 Digital Image Correlation	617
	7.3.2 Acoustic Emission	617
	7.3.3 Electromagnetic Emission	619
	7.3.4 In Situ Computed Tomography	620
	7.3.5 Method Combinations	621
	References	621
	Appendix A: Acoustic Emission-Parameters of Influence	625
	A.1 Acquisition System Electronics	625
	A.2 Sensing Technology	626
	A.3 Material and Geometry	627
	A.4 Experimental Configuration	629
	Appendix B: Material Properties	631
	Appendix C: Acoustic Emission Signal Parameters	635
	Appendix D: Definitions and Abbreviations	639
	Index	643