The authors previously proposed a method for the detection of fatigue cracks based on changes in the strain under an unloading condition near the weld toe. This method utilizes the strain change that occurs due to the release of residual stress introduced by the welding. However, the strain change near the weld toe becomes small once the fatigue crack has propagated. Therefore, this study focused on the area around the fatigue crack tip, where the authors found that fatigue crack propagation can be detected by monitoring changes in strain under the unloading condition.
