Development of Heat-Resistant Displacement Sensitive Sensor and Mechanism Elucidation of Environmental Assisted Cracking at Elevated Temperature by Inverse Processing of Dissipative Elastic Wave

研究目标是研制一种工作温度在600℃左右的面外位移敏感、耐热声发射换能器，研究环境辅助压裂的机理和动力学。我们开发了两种类型的耐热传感器。一种是电容式换能器，该换能器采用红外激光PVD沉积了薄的（3微米）无定形但化学计量的氧化铝薄膜。实验证明，该传感器具有宽频带特性，可在600℃以下的温度下精确测量面外位移。这种换能器的缺点是由于其高偏置电压而产生噪声。然后我们用LiNbO3元件开发了另一种锥形换能器，其居里温度在1000℃以上。与电容式传感器相比，该传感器的频带较窄，但能在600℃以下测量出高灵敏度的面外位移。由于传感器尺寸最小，使多通道监测成为可能。利用研制的换能器，首次测量了热奥氏体不锈钢AISI 340中纵波的速度频散和波衰减。我们还监测了304型钢在600℃下受到熔融氯化物和熔融银基焊料的声发射信号。利用研制的声发射系统，对快速断裂过程中产生的大量声发射信号进行了监测。通过对监测到的面外位移进行源模拟，估计出断裂动力学或断裂运动学和动力学。所开发的源仿真包括将第二类理论格林函数的卷积积分计算的位移与延迟函数和假设的源动力学与监测的源动力学相匹配。首次阐明了极快断裂与熔盐应力腐蚀开裂和熔点脆化有关。

Research aims to develop a out-of-plane displacement sensitive and heat resistant acoustic emission transducer which serves at temperature around 600C,and to study the mehanism and dynamics of environmentally assisted fracture. We developed two types of heat resistant transducer. One is the capacitive transducer with thin (3 micrometer) amorphous but stoichiometric alumina film which si deposited by the IR laser PVD.This sensor was demonstrated to be broad band and accurately measure the out-of-plane displacement at temperature below 600C.Disadvantage of this transducer is noise-generation due to its high bias voltage. Then we developed another conical-type transducer with a LiNbO3 element whose Curie temperature is above 1000C.Frequency band of this transducer is narrow compared withjthat of capacitive one, but it measures the out-of-plane displacement at high sensitivity below 600C.As the transducer size was minimized so as to make the multi-channel monitoring possible.Using the transducers developed, we first measured the velocity dispersion and wave attenuation of the longitudinal wave in hot austenitic atainless steel AISI 340. we also monitored AE signals from type 304 steel subjected to molten chlorides and fused silver-based solder at 600C.A number of AE signals from fast fracture were monitored by the developed AE system. The fracture dynamics, or the fracture kinematics and kinetics, were estimated by the souce simulation to the monitored out-of-plane displacement. The source simulation developed consists of matching the displacement computed by the convolution integral of the theoretical Green's function of the second kind with the retardation function and the assumed source dynamics to the monitored one. It was first elucidated that extremely fast fracture are associated with the molten salt stress corrosion cracking and fused solder embrittlement.