A Propagation Law of Small Fatigue Cracks

Abstract

It has been well established that the propagation process of through cracks under repeated stress can be treated by fracture mechanics. It has been also reported, however, that the propagation law of small fatigue cracks is quite different from that of through cracks and especially that in some materials the growth rate of small cracks cannot be treated as a function of stress intensity range. In this paper, the growth law of small fatigue cracks was investigated on the basis of a dislocation multiplication model. A new law was proposed on the analogy of the growth law of small creep cracks. The modified J-integral J^(N) (fatigue J-integral) which corresponds to the creep J-integral J' in the case of creep was defined, and it was shown that the growth rate of small fatigue cracks was proportional to J^(N).