The Study of Peculiar Fatigue Fracture Behavior of Ultrasonic Peened F690 Steel by New Threshold Stress Intensity Factor Range Equation

Abstract

In this study, a semi-circular crack with a crack depth of (0.4 – 1.6) mm was machined of DNV F690 offshore structural steel at a crack shape ratio a/c = 1.0. After ultrasonic peening (UP), the four-point bending fatigue test was conducted. The fatigue limit of short crack estimated by the equation proposed by Ando et al. decreased with increasing crack size, but was in good agreement with the fatigue limit obtained in the four-point bending fatigue test. The compressive residual stress increased the fatigue limit of the smooth specimen and crack specimen treated with UP. The fatigue limit of UP crack specimen with crack depth a = 0.8 mm was more than 95 % of the fatigue limit of smooth specimen. Semi-circular cracks up to a = 0.8 mm in crack depth could be rendered harmless by UP, but UP crack specimen of a = 1.2 mm could not be rendered harmless. It was estimated that the harmless crack depth of the UP crack specimen was a = 1.14 mm.