Mechanism of Environmental Assisted Cracking by the AE Source Inversion and Moment Tensor Analyzes

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Aming to clarify the mechanism of the so-called active path corrosion type stress corrosion cracking (APC-SCC), eight channel acoustic emission (AE) monitoring was attempted. The AE source inversion, moment tensor and radiation pattern analysis of the longitudinal waves revealed that the successive or multiple intergranular crackings were involved in the SCC of austenitic stainless steel AISI 304 by the polythionine acid solution at ambient temperature. Moment tensor analysis of the AE waves, however, showed an abnormal result because all sensors could not monitor the longitudinal wave emitted by the first fracture The out-of-plane displacement computed for two-step generation of microcracks was found to agree well with the monitored one.It was first demonstrated that the chloride-SCC of the AISI304 steel at 140C was associated with the transgranular brittle fracutre. We also proposed a new method to determine the experimental trasnfer function of the compact tension specimen. The out-of-plane displacement computed using the experimental transfer function of the specimen sharply agreed with the monitored one, and indieated that the extremely fast cracking, almost 10^7 times that of average SCC propagation rate, occured even in the transgranular chloride-SCC.The mechanism of the molten chloride salt and fused zinc attack of AISI 304 steel at 600C was also examined using the developed heat resistant capacitive AE sensor. Multiple cleavage type crackings were firstly revealed to occur even in these high temperature attacks.