Investigation of fatigue fracture using optical interferometer

This study aims to elucidate the fatigue fracture mechanism from the deformation behavior of the specimen experiencing fatigue. Electronic speckle pattern interferometry (ESPI) is used to measure the dynamic displacement field of the aluminum specimen under cyclic loading. The specimen was initially pulled up to a stress close to the tensile strength and then subjected to cyclic loading. ESPI yields interferometric fringe patterns that represent the contours of the differential displacement at a given time step (the displacement occurring during the interval between neighboring time steps). Deformation behavior was interpreted by observing the change in the fringe patterns until the specimen fractured. Our findings include (a) as the fatigue accumulates the deformation tends to involve rotation, (b) slight twisting the specimen around the loading axis causes a stress concentration, and (c) the stress concentration disappears and reappears at a different location of the specimen. In this presentation, we discuss these changes observed in the differential displacement field and their connection to fatigue damage accumulation.