Study On System Development And Performance Optimization Of Crack Growth Monitor Instrument Based On DCPD Method

Compact tensile(CT)specimen is used to the stress corrosion cracking(SCC)crack propagation experiment in an autoclave that simulates the nuclear power high-temperature and high-pressure environment,which is the main method to understand the environmental cracking(EAC)performance of nuclear power structural materials.Due to the limitations of the autoclave monitor environment,the potential drop method,including the direct current potential drop method(DCPD)and the alternating current potential drop method(ACPD),is the only way to monitor the crack growth of tensile specimens in real time.The crack signal characterized by the DCPD method is very weak,and it is susceptible to interference from the external environment and instrument system noise,temperature drift,and thermoelectric potential.This thesis,by studying the source and existence mechanism of signal interference in the monitoring system,the performance of the DCPD crack growth monitoring system developed by this laboratory has been Optimized and improved from the aspects of hardware,software,and monitor object probe points location,and finally built the third-generation DCPD crack growth monitoring instrument.The main research work completed are shown as follows.(1)According to the analysis of the measured data and application scenarios of the crack growth monitoring instrument,the main factors affecting the crack test accuracy under high temperature environment are determined,and on the basis of existing research,the monitoring system has been comprehensively improved and perfected,designed and implemented a crack growth monitoring system.(2)Based on the DCPD method,the overall scheme of the crack monitoring system was optimized,which greatly improved the monitoring performance of the instrument.The hardware completed the integration of functions such as acquisition circuit,communication circuit,signal amplification circuit and added the power-off storage function of data and the real-time interaction of the instrument The software used the reversed DCPD method,wavelet threshold method and reference potential law,optimized the thermoelectric potential,noise and temperature drift in the monitoring signal,and the performance indicators of the system have been significantly improved.(3)According to the monitoring principle of the DCPD method,a finite element model of the tensile specimen was established to obtain the potential value of the standard CT specimen under different crack lengths,and then the relationship between the crack length and the potential drop was calibrated.At the same time,a mathematical model of the measurability and crack independence of the reference potential difference was constructed,and the genetic algorithm(GA)was used to optimize the position of the probe points of the reference potential difference,and the parameters measured at the current input point and the upper right position of the CT specimens were obtained.The specific potential had the largest compensation for the main potential on both sides of the crack.(4)The third-generation of crack growth monitor instrument has been developed in our laboratory,the static and dynamic crack monitoring experimental platforms are built,crack monitoring experiments are carried out,and the optimization results of the instrument are quantitatively analyzed and verified in terms of the accuracy,resolution and stability of the test signals.