Abstract
Surface motions due to a disbonding of stainless overlay from base metal has been measured by the use of a commercially available flat-frequency displacement transducer. 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 emmission (AE) was found to be very sensitive and effective to monitor the disbonding. Some tens of AE events could be located by using two meaningful delta-t values. The detected waveforms due to the disbonding exhibited interesting variation as a function of the distance between the source epicenter and the transducer location. 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 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 of 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. It is shown that quantitative analysis of microfracture due to the disbonding can be readily made by comparison of experimentally measured surface displacements and theoretically calculated surface motions.
