Article ID: TETSU-2022-008
In this paper, fatigue tests of two different structural steels utilizing DIC technique were carried to evaluate fatigue crack initiation and propagation properties based on the local strain. At the bottom of the notch, hysteresis loop was observed after plastic deformation in the first cycle. The maximum strain and strain range of the hysteresis loop depended on the steel strength. In addition, the fatigue crack initiation life estimated from the strain range was almost in agreement with the fatigue test results. In the strain measurement around the fatigue crack, reasonable results were obtained by removing the fatigue crack part from the analysis area of DIC. The opening / closing behavior at each position of the fatigue crack could be evaluated by directly measuring the opening displacement. The position of the maximum strain near the fatigue crack moved according to the crack closure, and the peak position corresponded to the tip of open crack. The strain range at the tip of fatigue crack showed a good correlation with the fatigue crack propagation rate.