Service Load and Fatigue Strength : Report 6, Crack Initiation and Propagation under Repeated Varying Load

Abstract

To clarify the behavior of fatigue strength under service load from the view point of the crack propagation, fatigue tests under successively varying load were performed. In this paper, a prediction method for the crack propagation curve is proposed by applying the superposition law to the crack propagation of the annealed carbon steel specimens and the induction hardened carbon steel specimens, both of which are loaded under sinusoidally varying amplitude. Experimental results show that the Minor's law is applicable to the crack initiation for three materials : 0.17% and 0.36% carbon annealed and 0.17% carbon induction hardened steels. On the other hand, the superposition law is applicable to the induction hardened specimens, but is not applicable to the annealed ones and the results are situated in the dangerous side. Either, the effect of the period of varying load is not recognized in the present three materials.