Comparison between experimentally detected surface motions due to a disbonding of stainless overlay and simulated waveforms

Using a commercially available flat-frequency displacement transducer which produces excellent displacement response, we have measured surface motions due to a disbonding of stainless overlay from base metal. The experimental result showed that a buried tensile crack (penny-shaped crack) can be generated by hydrogen-induced disbonding of stainless weld overlay from base metal. Acoustic emission (AE) was found to be very sensitive and effective to monitor the disbonding. Planar source location using a set of three Δt values during this process was impossible because of bounded specimen configuration. However, some tens of AE events could be located by using two meaningful Δt values. The detected waveforms due to the disbonding exhibited interesting variation as a function of the distance between the epicenter of the source and the transducer location. This result suggests potential of a new source location method based on waveform measurement. On the basis of the theory of elastodynamics and dislocation models, simulation analysis was made for surface motions due to a penny-shaped crack parallel and inclined to the stress-free surface in a half-space. Simulated waveforms were obtained as a function of the distance between the epicenter and the observation position. Comparison between the detected and simulated waveforms indicated remarkable agreement in the early time response. This excellent agreement demonstrates the applicability of the transducer and the present simulation analysis to quantitative waveform analysis relating to fundamental AE work.