Abstract
In order to elucidate the microkinetics of hydrogen assisted cracking of alloys, new AE source inversion processing utilizing theoretical Green's function was proposed. In this processing, surface displacement detected by a displacement sensor was deconvoluted by the theoretical Green's function for dipole source, and the energy released by crack formation was obtained. This processing, however, becomes possible when some special conditions were satisfied, so detail experiments on sensor calibration, radiation pattern of longitudinal wave (P-wave), wave distortion by reflected P-wave, were done using three channel AE data acquisition system (ADAS) developed by us. It was found that about half of the detected waves during hydrogen assisted cracking were generated by the the Mode-I type microcracks, and could be inversion processed by the proposed method. Another half were found to be the waves emanated by mixed mode cracking. Source waves suggest that new surface with diameter of few ten micrometers are created with time of 1 to 5 microsecond. Intergranular cracks in the MnS segregated zone sandwiched by dimple fracture in the front of macroscopic crack tip where the highest hydrostatic pressure exists might correspond to the source waves obtained by this method. The number of AE waves and these intergranular cracks agreed well.
