Strain distribution measurement with digital image correlation method by using metallographic image under cyclic loading

Abstract

In order to investigate the relationship between strain distribution and fatigue crack growth behavior, the digital image correlation (DIC) method was applied for strain distribution measurement at crack tip during SEM in-situ observation fatigue crack growth test. The result showed that a straight crack had an elliptical strain concentration area at the fatigue crack tip. On the other hand, when crack branching occurred, strain concentration area was found to be inclined and was including dense slip band region. After some number of cycles, crack tended to propagate along the strain concentrated area. Additionally, local cyclic strain hardening was confirmed by micro vickers hardness test at the strain concentrated area with dense slip band.