ABSTRACT
The authors have previously proposed a method to evaluate fatigue crack initiation by monitoring changes in strain near the weld toe under unloading conditions. In this method, the alteration in strains resulting from the release of residual stress is utilized. However, if fatigue cracking has already initiated, the change in strain under the unloading condition at the weld toe is minimal. Therefore, the authors shifted their focus to the area around the fatigue crack tip. In this study, it was discovered that fatigue crack propagation can be detected through changes in strain under unloading conditions. Furthermore, considering the application to monitoring in real bridges, wireless strain measurement logger with LPWA was used to measure the strain at the crack tip under unloading conditions. It was found that the measurement results of the strain logger with LPWA show the same tendency to those of dynamic strainmeters.
