Evaluation of strain change under unloading conditions by initiation and propagation of fatigue crack

Abstract

In this research, the authors focus on the strain under unloading conditions to detect the fatigue crack in welded structures. The fatigue tests of out-of-plane gusset joint under stress ratio R = -1 were carried out by measuring the strain every 10 thousand cycles. As the fatigue crack initiates and propagates, the mean strain which corresponds with the strain under the unloading conditions measured near the weld toe becomes smaller. This is because that the release of the tensile residual stress introduced by the welding. On the other hand, it was shown that the mean strain measured at the compressive residual stress region gradually increases by the crack initiation and propagation. Additionally, the appropriate location of strain gauges was discussed.