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Intro; Supervisor's Foreword; Parts of this thesis have been published in the following journal articles:Li, D. *, Kuang, K. S. C., Koh, C. G. (2017). Rail crack monitoring based on Tsallis synchrosqueezed wavelet entropy of acoustic emission signals: a field study. Structural Health Monitoring. Prepublished online December 4, 2017, DOI: 10.1177/1475921717742339.Li, D., Kuang, K. S. C. *, Koh, C. G. (2017). Fatigue crack sizing in rail steel using crack closure-induced acoustic emission waves. Measurement Science and Technol; Acknowledgements; Contents; Abbreviations; Nomenclature
List of FiguresList of Tables; Summary; 1 Introduction; 1.1 Background; 1.2 Objectives and Scope of Research; 1.3 Research Significance; 1.4 Thesis Outline; References; 2 Literature Review; 2.1 Common Defects of Rail Track; 2.1.1 Surface Cracks; 2.1.2 Internal Cracks; 2.2 Current Rail Monitoring Techniques; 2.2.1 Acceleration-Based Technique; 2.2.2 Automated Visual Technique; 2.2.3 Ultrasonic Techniques; 2.2.4 Electromagnetic Techniques; 2.2.5 Magnetic Induction Technique; 2.3 AE Technique and Its Applications; 2.3.1 Introduction to AE Technique; 2.3.2 Characterization of AE Waves
2.3.3 Relevant Applications of AE Technique2.4 State-of-Art of Rail Condition Monitoring Using AE; References; 3 Propagation Features and Source Location; 3.1 Introduction; 3.2 Experimental Procedure; 3.2.1 Pencil Lead Break (PLB); 3.2.2 Field PLB Test; 3.2.3 Field Train Pass-by Test; 3.2.4 AE Data Acquisition; 3.3 Time-Frequency Representation of AE Waves; 3.3.1 Continuous Wavelet Transform (CWT); 3.3.2 Optimal Mother Wavelet Selection; 3.3.3 Time-Frequency Characteristics of AE Waves; 3.4 Propagation Features of AE Waves; 3.4.1 Theory of Ultrasonic Propagation
3.4.2 Attenuation of AE Waves in Rail Head3.4.3 Dispersion of AE Waves in Rail Head; 3.5 Source Location Methods; 3.5.1 Time-of-Arrival (TOA) Method; 3.5.2 Wavelet Transform-Based Modal Analysis Location (WTMAL) Method; 3.6 Hilbert Transform-Based Noise Cancellation Method; 3.7 Results and Discussion; 3.7.1 Influence of Operational Noise on Crack Detection; 3.7.2 Source Location Without Noise Using TOA Method; 3.7.3 Source Location Without Noise Using WTMAL Method; 3.7.4 Source Location with Noise Using WTMAL Method; 3.8 Concluding Remarks; References; 4 Sizing of Fatigue Cracks
4.1 Introduction4.2 Experimental Procedure; 4.2.1 Rail Steel Specimens; 4.2.2 Fatigue Tests; 4.2.3 AE Data Acquisition; 4.2.4 Crack Length Calculation; 4.2.5 Crack Surface Observation; 4.3 AE Wave Classification; 4.3.1 Wavelet Power (WP)-Based Classification Index; 4.3.2 Threshold Determination for the Classification Index; 4.3.3 Frequency Bands Selection for the Classification Index; 4.4 Fatigue Crack Sizing Methods; 4.4.1 Traditional Method Based on CP-Induced AE Waves; 4.4.2 Novel Method Based on CC-Induced AE Waves; 4.4.3 Comparison of Crack Sizing Methods; 4.5 Results and Discussion
List of FiguresList of Tables; Summary; 1 Introduction; 1.1 Background; 1.2 Objectives and Scope of Research; 1.3 Research Significance; 1.4 Thesis Outline; References; 2 Literature Review; 2.1 Common Defects of Rail Track; 2.1.1 Surface Cracks; 2.1.2 Internal Cracks; 2.2 Current Rail Monitoring Techniques; 2.2.1 Acceleration-Based Technique; 2.2.2 Automated Visual Technique; 2.2.3 Ultrasonic Techniques; 2.2.4 Electromagnetic Techniques; 2.2.5 Magnetic Induction Technique; 2.3 AE Technique and Its Applications; 2.3.1 Introduction to AE Technique; 2.3.2 Characterization of AE Waves
2.3.3 Relevant Applications of AE Technique2.4 State-of-Art of Rail Condition Monitoring Using AE; References; 3 Propagation Features and Source Location; 3.1 Introduction; 3.2 Experimental Procedure; 3.2.1 Pencil Lead Break (PLB); 3.2.2 Field PLB Test; 3.2.3 Field Train Pass-by Test; 3.2.4 AE Data Acquisition; 3.3 Time-Frequency Representation of AE Waves; 3.3.1 Continuous Wavelet Transform (CWT); 3.3.2 Optimal Mother Wavelet Selection; 3.3.3 Time-Frequency Characteristics of AE Waves; 3.4 Propagation Features of AE Waves; 3.4.1 Theory of Ultrasonic Propagation
3.4.2 Attenuation of AE Waves in Rail Head3.4.3 Dispersion of AE Waves in Rail Head; 3.5 Source Location Methods; 3.5.1 Time-of-Arrival (TOA) Method; 3.5.2 Wavelet Transform-Based Modal Analysis Location (WTMAL) Method; 3.6 Hilbert Transform-Based Noise Cancellation Method; 3.7 Results and Discussion; 3.7.1 Influence of Operational Noise on Crack Detection; 3.7.2 Source Location Without Noise Using TOA Method; 3.7.3 Source Location Without Noise Using WTMAL Method; 3.7.4 Source Location with Noise Using WTMAL Method; 3.8 Concluding Remarks; References; 4 Sizing of Fatigue Cracks
4.1 Introduction4.2 Experimental Procedure; 4.2.1 Rail Steel Specimens; 4.2.2 Fatigue Tests; 4.2.3 AE Data Acquisition; 4.2.4 Crack Length Calculation; 4.2.5 Crack Surface Observation; 4.3 AE Wave Classification; 4.3.1 Wavelet Power (WP)-Based Classification Index; 4.3.2 Threshold Determination for the Classification Index; 4.3.3 Frequency Bands Selection for the Classification Index; 4.4 Fatigue Crack Sizing Methods; 4.4.1 Traditional Method Based on CP-Induced AE Waves; 4.4.2 Novel Method Based on CC-Induced AE Waves; 4.4.3 Comparison of Crack Sizing Methods; 4.5 Results and Discussion