Local plastic deformation behaviour around crack tip under cyclic loading

The change of mechanical property at stress concentration parts under cyclic loading play an important role in fatigue process in metal. In this study, the change of material property, that is, the cyclic hardening/softening phenomena at early stage of fatigue around crack tip were measured by using Dynamic Ultra-Micro Hardness Tester(DHU-201S).(1) The effect of the stress concentration, the strain amplitudes and number of cycles on the dynamic micro hardness ( hardness evaluated by indentation depth) and the indentation of material surface were examined in detail. The cyclic local plastic behavior good agree with the change of surface micro dynamic hardness and it is shown that this micro indentation test is effective method as the prediction of the cumulative damage by low cycle fatigue.