ABSTRACT I ACKNOWLEDGMENTS II TABLE OF CONTENTS III LIST OF TABLES VI LIST OF FIGURES VIII SYMBOLS XIV CHAPTER I INTRODUCTION 1 1.1 General Introduction and Motivations 1 1.2 References Review 3 1.3 Thesis structure 3 CHAPTER II MODEL VALIDATION 4 2.1 Plane Stress approach and Elements used 4 2.2 Material properties and fiber orientation control 5 2.2.1 Material Models 5 2.2.2 Fiber Orientation considerations and matrices 6 2.2.2.A Orthotropic materials and matrices 7 2.2.2.B Fibers rotation 10 2.2.3 Material properties input check 14 2.2.3.A Results comparison to uniform loading theoretical results 16 2.2.3.B Results comparison between ANSYS and BEM-AEPH 18 2.3 Mesh considerations in regards to the loading 22 2.3.1 Load and signal choice 22 2.3.1.A Impulse load choice 22 2.3.1.B Signal choice and impulse characteristics 23 2.3.1.C Impulse load frequency and study time increment 29 2.3.2 Mesh size and Convergence study 31 2.4 Cracked Models Geometry 34 2.4.1 Model & Crack creation 34 2.4.2 Regular and Concentration Point-based meshes 38 2.5 Boundary Conditions and Mesh considerations in regards to the cracks 41 2.5.1 Stresses verification in regards to long time responses 41 2.5.2 Mesh type in regards to the cracks 45 2.5.2.A Theoretical Stress Intensity Factor 45 2.5.2.B Concentration Point-based mesh 47 2.5.2.C Uniform straight mesh 53 2.5.2.D Results summary and mesh discussion 60 2.5.2.E Convergent Concentration Point-based mesh and mesh choice 62 CHAPTER III RESULTS 67 3.1 Approach and Process 67 3.1.1 General Principles of the approach 67 3.1.2 Simulation Process 69 3.2 Crack Detection results 71 3.2.1 Fully centered flat crack 71 3.2.1.A Fully centered crack with regular 12.5 mm mesh 72 3.2.1.B Fully centered crack with concentrated 12.5 mm mesh 76 3.2.1.C Fully centered crack with concentrated 3.125 mm mesh 78 3.2.2 Decentered flat cracks 81 3.2.2.A Decentered left crack 81 3.2.2.B Decentered right crack 84 3.2.3 Tilted cracks 87 3.2.3.A Centered 10° tilted crack 87 3.2.3.B Decentered left -15° tilted crack 90 3.3.4 Multiform cracks 93 3.3.4.A Multiform crack with a 10° tilted part 93 3.3.4.B Multiform crack with a -15° tilted part 96 3.2.5 Multiple cracks 99 3.2.5.A Decentered Flat and -15° Multiform cracks 99 3.2.5.B Multiform crack with a 10° tilted part and fully decentered flat crack 103 3.2.6 Crack Detection summary 107 3.3 Effect of the material properties on wave speed 110 3.3.1 Analysis Process 110 3.3.2 Material Influence Results 112 3.3.2.A Fibers influence on wave propagation for Kevlar/Epoxy 113 3.3.2.B Fibers influence on wave propagation for Carbon/Epoxy 117 3.3.2.C Fibers influence on wave propagation for Glass/Epoxy 120 3.3.2.D Material Influence summary 123 CHAPTER IV CONCLUSION 124 4.1 General Conclusion 124 4.2 Approach Pros and Cons 129 4.3 Suggestions 129 REFERENCES 130 APPENDIX TABLE 131