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

研究目的是研制一种温度在600℃左右的离面位移敏感耐热声发射换能器，并研究环境辅助断裂的机理和动力学。我们研制了两种耐热换能器。一种是用红外激光PVD淀积的化学计量比非晶氧化铝薄膜的电容式传感器，该传感器是一种宽带的传感器，可以在600C以下的温度下精确测量离面位移。在此基础上，我们又研制了一种居里温度在1000℃以上的LiNbO_3圆锥型换能器。该换能器与电容式换能器相比频带较窄，但在600C以下的高灵敏度下可以测量离面位移。由于换能器的尺寸减小，使得多通道监测成为可能。我们还监测了在600℃熔融氯化物和熔融银基焊料作用下304钢的声发射信号。利用研制的声发射系统监测了大量快速断裂的声发射信号。通过对监测到的离面位移进行震源模拟，估算出断裂动力学，即断裂运动学和动力学。所开发的震源模拟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定的震源动力学与监测的震源动力学相匹配。首次阐明了极快断裂与熔盐应力腐蚀开裂和熔融焊料脆化有关。

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.