Abstract
Fatigue and impact fatigue tests have been carried out on carburized steels with the case between 0.3 and 0.5 mm.
S-Nf curves in impact fatigue tests show a knee transition point as well as in fatigue tests. The crack initiates from the surface of the specimen in the cycle life region lower than the transition point, while that initiates from the inside of the specimen in the cycle life region higher than the transition point in both fatigue and impact fatigue tests. The fish-eye fracture appears when the crack initiates from the inside of the specimen. The transition on S-Nf curve is attributed to the difference in such a crack initiation site. Striations have been observed in the fish-eye fracture area in both fatigue and impact fatigue tests. The crack growth rate calculated from the space of striations in impact fatigue tests is higher than that in fatigue ones. The cyclic impact loading has been found to accelerate the release of dislocations and damage of grain boundaries comparing with non-impact cyclic loading.
