UNIVERSITY OF CALIFORNIA, SAN DIEGO Non-contact Ultrasonic Guided Wave Inspection of Rails: Next Generation Approach A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Structural Engineering by Stefano Mariani Committee in Charge: Professor Francesco Lanza di Scalea, Chair Professor David J. Benson Professor Michael J. Buckingham Professor William S. Hodgkiss Professor Chia-Ming Uang 2015 Copyright, Stefano Mariani, 2015 All rights reserved. The dissertation of Stefano Mariani is approved, and it is acceptable in quality and form for publication on microfilm and electronically: ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ Chair University of California, San Diego 2015 iii DEDICATION To Bob iv TABLE OF CONTENTS Signature Page iii Dedication iv Table of Contents v List of Abbreviations ix List of Figures xi List of Tables xxii Acknowledgments xxiv Vita xvii Abstract of the Dissertation xxix 1 Introduction ................................................................................................................... 1 1.1 Non Destructive Evaluation of railroad tracks. Introductory discussions and motivations for the research ............................................................................................ 1 1.2 Outline of the numerical and experimental approach of the dissertation ................. 3 2 State of the art review ................................................................................................... 5 2.1 Development of structural defects in rails ................................................................ 5 2.1.1 Transverse defects in the rail head .................................................................. 8 2.1.2 Longitudinal defects in the rail head ............................................................. 16 2.1.3 Web defects ................................................................................................... 19 2.1.4 Base defects ................................................................................................... 22 2.1.5 Rolling contact fatigue conditions ................................................................. 23 2.1.6 Defective welds ............................................................................................. 31 2.2 Current rail inspection methods ............................................................................. 32 2.2.1 Historical background ................................................................................... 32 v 2.2.2 Currently used methods ................................................................................. 34 2.3 Ultrasonic guided waves for defect detection in rails ............................................ 41 3 Concepts of the proposed rail defect detection system ............................................... 47 3.1 Introduction ............................................................................................................ 47 3.2 Former UCSD rail inspection system based on a hybrid laser/air-coupled configuration ................................................................................................................. 48 3.3 Newly developed rail inspection system solely based on air-coupled transducers 50 3.3.1 Current transducers configuration ................................................................. 50 3.3.2 Alternative transducers configurations tested over the course of the research project ....................................................................................................................... 59 3.4 Conclusions ............................................................................................................ 61 3.5 Acknowledgments .................................................................................................. 62 4 Numerical modeling of ultrasonic guided wave propagation: theoretical fundamentals and application to the rail case .......................................................................................... 63 4.1 Introduction and theoretical fundamentals ............................................................. 63 4.1.1 Ultrasonic waves propagation in an unbounded medium ............................. 66 4.1.2 Guided waves propagation in a bounded medium ........................................ 68 4.2 Local Interaction Simulation Approach (LISA) ..................................................... 76 4.2.1 Introduction ................................................................................................... 76 4.2.2 Proof of concept of the proposed rail defect detection system ...................... 78 4.2.3 Distribution of wave energy on the rail top surface ...................................... 86 4.2.4 Parametric study of the prototype sensitivity to different defect conditions . 99 4.2.4.1 Case I: signals not affected by noise (ideal condition) 109 4.2.4.2 Case II: noise artificially added to the signals (realistic condition) 121 vi 4.2.4.3 Case II: probabilistic analysis through computation of Receiver Operating Characteristics curves (for “high” SNR levels) 139 4.2.4.4 Case II: probabilistic analysis through computation of Receiver Operating Characteristics curves (for “low” SNR levels) 148 4.2.4.5 Case II: comparison with results obtainable using coherent array techniques 154 4.2.5 Future works ................................................................................................ 169 4.3 Finite element analysis of the complete experimental setup using LS-DYNA .... 170 4.3.1 Introduction ................................................................................................. 170 4.3.2 Finite element analysis of the pressure field generated in air by a cylindrically focused air-coupled transmitter .......................................................... 172 4.3.3 Simulation of the complete ultrasonic wave propagation through air and rail . ..................................................................................................................... 186 4.3.4 LS-DYNA aid in the design of a dedicated holder for a newer transmitter 205 4.4 Conclusions .......................................................................................................... 218 4.5 Acknowledgments ................................................................................................ 219 5 Development of the rail inspection prototype ........................................................... 221 5.1 Introduction .......................................................................................................... 221 5.2 UCSD/FRA Rail Defect Testing Facility ............................................................. 223 5.3 Prototype parts design .......................................................................................... 224 5.4 Electronic hardware layout ................................................................................... 226 5.5 Signal processing techniques employed to enhance the signal-to-noise ratio of the acquired waveforms .................................................................................................... 230 5.5.1 Digital filtering techniques (used in former versions of the prototype) ...... 231 5.5.2 Electrical impedance matching networks .................................................... 233 5.6 Statistical algorithm designed to enhance the rail defect detection performance 237 vii 5.6.1 Defect-sensitive features extraction ............................................................ 242 5.7 On the issue affecting higher speed testing performance ..................................... 250 5.8 Field test at Transportation Technology Center ................................................... 256 5.8.1 Introduction ................................................................................................. 256 5.8.2 Operational parameters used during the execution of the tests and test site lay-out ..................................................................................................................... 258 5.8.3 Field test timeline ........................................................................................ 261 5.8.4 Field test results: Damage Index traces ....................................................... 263 5.8.5 Field test results: Receiver Operating Characteristic curves ....................... 266 5.8.6 Conclusions ................................................................................................. 270 5.9 Further studies conducted on the field test data ................................................... 271 5.10 Conclusions ......................................................................................................... 274 5.11 Acknowledgments ............................................................................................... 276 6 Conclusions ............................................................................................................... 277 6.1 Review of the dissertation and summary of the results ........................................ 277 6.2 Recommendations for future work ....................................................................... 280 References ......................................................................................................................