Monitoring of Acoustic Emission Activity of Smart Stress Memory Patch to Estimate Maximum Fatigue Stress for Structural Health Monitoring

Abstract

A new sensing tool called the smart stress memory patch, which is made of a pure Cu cracked specimen with thin thickness, has been proposed in our previous study to estimate fatigue damage such as maximum fatigue stress, number of cycles and stress amplitude for structural health monitoring. In this study, the acoustic emission (AE) activity of pure Cu specimens heat treated under several conditions was investigated because the maximum fatigue stress can be estimated on the basis of the AE onset stress in the Kaiser effect. The obtained AE onset stress was proportional to the yield stress, and the notch sensitivity of the AE onset stress was not observed. The Kaiser effect in Cu specimens with various grain sizes was examined during reloading. The AE onset stress of the Cu specimen with a large grain size during reloading was lower than the previous maximum stress, while the AE onset stress of that with a small grain size was almost equal to the maximum stress in the first loading. The applied maximum stress in fatigue loading was compared with the AE onset stress and the result shows that a suitable stress range for a smart stress memory patch can be obtained using the heat-treated and notch-introduced electrodeposited Cu specimen.