New Trends in Structural Health Monitoring (eBook)

Preface 6
Contents 8
Structural Health Monitoring – Its Association and Use 9
1 A Motivation for Structural Health Monitoring 9
2 Loads and Overloads 19
3 Fatigue, Fracture and Damage Tolerance 26
3.1 Fatigue 26
3.2 Fracture and Damage Tolerance 30
3.3 SHM, Loads Monitoring and Damage Tolerance 43
4 Non-Destructive Evaluation – Some Basic Principles 44
4.1 Historic Background 44
4.2 Magnetism 45
4.3 Electromagnetic Ultrasound (EMUS) 54
4.4 Eddy Current 55
4.5 Ultrasonics 58
4.6 Other Conventional NDT Techniques and Emerging Technologies 58
5 Non-Destructive Evaluation in Composite Materials 62
6 Approaches to Structural Health Monitoring 67
7 Emerging SHM Applications and Concluding Remarks 80
Bibliography 84
Further Reading 87
Structural Health Monitoring of Aircraft Structures 88
1 Introduction 88
2 Structural Health Monitoring Architectures 90
2.1 Sensors Network Architecture 91
2.2 Phased Arrays Architecture 94
3 Piezoelectric Networks 97
3.1 Damage Detection: Metallic Plates 100
3.2 Development of a PCB Board for System Automation 107
3.3 Damage Detection: Composite Plates 109
3.4 Initial Acoustic Emission Experiments 115
4 Phased Arrays 119
4.1 Dispersion Curves 122
4.2 Tuned Lamb Waves: Mode, Frequency and Transducer Selection 123
4.3 Number of Elements in the Array 125
4.4 Phased Array Actuation System 126
4.5 Damage Detection Algorithms 129
4.6 Damage Detection: Metallic Plates 134
5 SHM using Fiber Optic Sensors 137
5.1 Fiber Bragg Grating Sensors 141
5.2 Etched Fiber Sensors 141
5.3 Sensor Characterization 142
5.4 Flow Monitoring 144
5.5 Flow Monitoring of Panel Specimen 144
5.6 Flow Monitoring of 3D Semicircle Specimen 146
5.7 Strain Sensitivity Characterization 148
5.8 Strain Sensitivity of Panel Specimen 150
5.9 Strain Sensitivity of Semicircular Specimen 151
6 Concluding Remarks 152
Bibliography 153
Vibration-Based Damage Diagnosis and Monitoring of External Loads 156
1 Introduction 156
2 Modeling and Diagnosis of Damaged Systems 158
2.1 General Non-Linear Dynamical Model 158
2.2 Feature Extraction 159
2.3 Residual Vector and Damage Indicator 160
2.4 Model-Based Diagnostics vs. Data-Based Damage Detection 161
3 Diagnosis of Linear Systems 164
3.1 Equation of Motion and State Space Representation 164
3.2 Damage Identification in the Modal Domain 165
3.3 Electro-Mechanical Impedance Method (EMIM) 167
3.4 Time Domain Methods 168
4 Data-based Damage Detection under Changing Environmental and Operational Conditions (EOC) 173
4.1 Overview of Methods 173
4.2 Environmental and operational conditions for wind energy plants 174
4.3 Compensation of environmental effects on damage detection approach using fuzzy classification 175
4.4 Example: Wind turbine 178
5 Reconstruction of External Loads 180
5.1 Problem overview and previous work 180
5.2 Design of Simultaneous state and input estimator 192
5.3 Application Examples 200
6 Conclusions 205
Bibliography 207
Statistical Time Series Methods for Vibration Based Structural Health Monitoring 216
1 Introduction 216
2 The General Workframe 219
2.1 The Structural States and the Data Sets 219
2.2 The Baseline and Inspection Phases 220
2.3 Classes of Statistical Time Series SHM Methods 222
3 Statistical Time Series Models of the Structural Dynamics 223
3.1 Non-Parametric Models 224
3.2 Parametric Models 225
3.3 Identification of Time Series Models 229
4 Selected Non-Parametric Time Series SHM Methods 231
4.1 PSD Based Method 232
4.2 FRF Magnitude Based Method 233
5 Selected Parametric Time Series SHM Methods 235
5.1 Model Parameter Based Methods 236
5.2 Model Residual Based Methods 238
5.3 Functional Model (FM) Based SHM Methods 245
6 Application of the Methods to a Laboratory Truss Structure 248
6.1 The Laboratory Truss Structure and Problem Definition 248
6.2 Baseline Phase: Structural Identification 250
6.3 Inspection Phase: SHM via Selected Non-Parametric Methods 252
6.4 Inspection Phase: SHM via Selected Parametric Methods 254
6.5 Discussion 258
7 Concluding Remarks and Future Research 261
Bibliography 263
A Appendix: Central limit theorem and statistical distributions associated with the normal 270
A.1 The Central Limit Theorem (CLT) 270
A.2 The x² distribution 270
A.3 The Student’s t distribution 271
A.4 The Fisher’s F distribution 271
Fiber Optics Sensors 272
1 Introduction 272
2 Classification of Fiber Optic Sensors 274
2.1 Intensity-based sensors 275
2.2 Phase modulated optical fiber sensors, or Interferometers. 277
2.3 Wavelength based sensors, or Bragg gratings. 278
3 Fiber Bragg Gratings as Strain and Temperature Sensors 281
3.1 Response of the FBG to uniaxial uniform strain fields. 282
3.2 Sensitivity of the FBG to temperature. 282
3.3 Response of the FBG to non-uniform uniaxial strain field. 283
3.4 Response of the FBG to transverse stresses. 285
3.5 Commercial FBG interrogation systems. 292
4 Structures With Embedded Fiber Bragg Gratings 292
4.1 Orientation of the optical fiber optic respective to the reinforcement fibers. 294
4.2 Ingress/egress from the laminate. 295
5 Examples of Applications in Aeronautics and Civil Structures 295
5.1 Stiffened panels with embedded fiber Bragg gratings. 296
5.2 Concrete beam repair 299
6 Distributing Sensing 301
7 Applications of Distributed Sensing 307
8 Final Comments 317
Bibliography 319
Damage localisation using elastic waves propagation method. Experimental techniques. 324
1 Structural Health Monitoring based on elastic waves propagation 324
2 Elastic waves 326
3 Elastic wave generation and sensing 334
3.1 Elastic waves generation techniques 334
3.2 Elastic waves sensing techniques 338
4 Wave generation and sensing equipment 345
5 Transducer network configurations 347
6 Energy summing algorithm 351
6.1 Basis for numerical algorithm 351
6.2 Results 355
6.3 Summary 361
7 Beam forming algorithm 363
7.1 Basis for numerical algorithm 363
7.2 Results 367
7.3 Summary 372
Bibliography 374
Application for Wind Turbine Blades 379
1 A look at the Wind Energy Industry 379
2 Condition Monitoring of Wind Turbine Blades 385
3 Damage in Polymer Composite Materials 396
4 Structural Testing of Wind Turbine Blades 412
5 Future work Smart blades?
Bibliography 432