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

为了弄清所谓的活性路径腐蚀型应力腐蚀开裂(APC-SCC)的机理，尝试了八通道声发射(AE)监测。AE源反转、力矩张量和纵波辐射谱分析表明，在常温下，AISI304奥氏体不锈钢在聚亚硫氨酸溶液中发生了连续或多次沿晶开裂。然而，由于所有的传感器都不能监测到第一次断裂所发出的纵波，所以对声发射波矩张量分析的结果是异常的。两步产生微裂纹的离面位移计算结果与监测结果吻合较好。首次证明了AISI304钢在140℃时的氯化应力腐蚀开裂与穿晶脆性断裂有关。我们还提出了一种确定紧凑拉伸试件实验传递函数的新方法。用试件的实验传递函数计算的离面位移与监测值吻合很好，表明即使在穿晶的氯化物-应力腐蚀混凝土中也出现了极快的裂纹，几乎是平均应力腐蚀扩展速率的10.7倍。用研制的耐热电容式声发射传感器研究了600℃下AISI 304钢熔融氯盐和熔融锌的腐蚀机理。首次发现，即使在高温下也会发生多解理型开裂。

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.