Contents
List of Figures vii
1 Introduction 1
1.1 Non-destructive Evaluation . . . 2
1.2 Structural Health Monitoring . . . 4
1.2.1 Structural Health Monitoring techniques . . . 6
1.2.2 Wave based techniques in Structural Health Monitoring . . . 8
1.3 Lamb wave based damage identi cation con gurations . . . 10
1.4 The eect of environmental conditions for SHM . . . 11
1.5 Objective . . . 13
1.6 Dissertation overview . . . 17
2 Temperature eect of Lamb wave based damage detection 21 2.1 Literature overview . . . 21
2.1.1 Temperature eect on Lamb waves . . . 21
2.1.2 Multiple environmental eects on guided and Lamb waves . . . . 24
2.2 Numerical methods for wave propagation modelling . . . 25
2.3 Summary . . . 27
3 Lamb waves - theoretical background 28 3.1 Introduction to Lamb waves . . . 28
3.2 Lamb wave sensitivity to thermal uctuation . . . 34
3.3 Change of dispersion curves under temperature variation . . . 37
3.4 Summary . . . 39
CONTENTS
4 The Local Interaction Simulation Approach for wave propagation
mod-elling 40
4.1 The LISA algorithm . . . 40
4.2 Parallel architecture on graphical cards - LISA implementation . . . 42
4.3 Numerical errors and discrepancies . . . 44
4.3.1 Numerical dispersion and stability condition . . . 44
4.3.2 Dissipation . . . 45
4.3.3 Edge re ections . . . 47
4.4 Examples of LISA implementation . . . 48
4.4.1 The LISA for plate like structure . . . 48
4.4.2 The LISA for rail inspection . . . 50
4.4.2.1 Numerical model of guided wave propagation . . . 50
4.4.2.2 Numerical results . . . 50
4.4.2.3 Experimental set-up for guided wave air-coupled in rail 54 4.4.2.4 Experimental results . . . 55
4.5 Thermal eect implementation for LISA approach . . . 57
4.6 Summary . . . 58
5 Lamb wave propagation modelling under varying temperature 59 5.1 Background . . . 59
5.2 Experimental tests . . . 60
5.3 Numerical model implementation . . . 63
5.3.1 Temperature dependent LISA algorithm . . . 64
5.3.2 Numerical model of Lamb wave propagation . . . 65
5.4 Analysis of Lamb wave features - experimental and numerical comparison 67 5.4.1 Peak-to-peak amplitude . . . 67 5.4.2 Arrival time . . . 69 5.4.3 Time delay . . . 70 5.4.4 Instantaneous phase . . . 71 5.5 Summary . . . 77 ii
CONTENTS
6 Two-dimensional actuation stress modelling of piezoceramic transduc-ers under temperature eld uctuation 79
6.1 Background . . . 80
6.2 Actuation and sensing time-dependent models for Lamb wave propaga-tion - problem formulapropaga-tion . . . 81
6.3 Actuation stress models . . . 83
6.3.1 Theoretical model . . . 84
6.3.2 Numerical model . . . 86
6.4 Results . . . 87
6.4.1 Actuated in-plane shear and normal stresses . . . 87
6.4.1.1 The eect of transducer's stiness . . . 87
6.4.1.2 The eect of adhesive layer's stiness . . . 91
6.4.1.3 The eect of excitation frequency . . . 94
6.4.2 The eect of temperature on piezoceramic transducers . . . 96
6.5 Summary . . . 101
7 Three-dimensional transducer modelling under temperature eld vari-ation 103 7.1 Time-dependent Lamb wave propagation . . . 103
7.1.1 Problem examined . . . 103
7.1.2 Numerical simulations . . . 104
7.1.2.1 Finite element model . . . 104
7.1.2.2 Voltage response . . . 106
7.1.3 Experimental validation . . . 108
7.2 Results and discussion . . . 109
7.2.1 Lamb wave amplitude . . . 110
7.2.2 Electric eld response . . . 114
7.3 Summary . . . 116
8 Temperature eect for the plate-bond-transducer structure used in wave propagation 117 8.1 Eect of temperature on Lamb wave generation, propagation and sensing 117 8.2 Proportional in uence of model components on Lamb wave response . . 122
8.3 Summary . . . 124
CONTENTS
9 Temperature eect in Lamb wave based damage localisation using Macro Fiber Composite 125
9.1 Background . . . 126
9.2 Response of MFC piezo-composite sensors to Lamb waves . . . 127
9.2.1 Straight-crested wavefronts . . . 127
9.2.2 Circularly-crested wavefronts . . . 130
9.3 MFC rosettes for wave source location . . . 133
9.4 MFC rosettes for damage location . . . 136
9.4.1 Experimental setup and procedure . . . 136
9.4.2 Wave direction estimation . . . 137
9.4.3 Damage location estimation under temperature variation . . . 142
9.5 Summary . . . 144
10 Conclusions 147 10.1 Summary of the presented work . . . 147
10.2 Main conclusions and achievements . . . 149
10.3 Future work proposal . . . 150
References 151
A Shape functions for hexahedron elements 173 B List of publications related to presented research work 174
