Quantitative evaluation of fatigue crack using nonlinear guided waves in pipelines

This thesis investigates the interaction between nonlinear guided waves and fatigue crack at its initiation in metallic pipes. Literature review in terms of guided wave propagation and interaction with damage through linear and nonlinear characteristics in pipe structures are introduced. Theoretical analysis is extended from plate-like to pipe-like scenario and a proper nonlinear index is developed to assess the severity of fatigue crack of a pipe. The detection of fatigue crack in pipe structures with second harmonic generation method is then conducted numerically and experimentally. The relation between crack length and nonlinearity induced by a fatigue crack is assessed quantitatively.