Threshold and Plastic Work of Fatigue Crack Propagation in HY80 and HY130 Steels

摘要

The objective of the present research was to make a comprehensive study of the effect of heat treatment and microstructure on the fatigue crack propagation rate from the threshold stress intensity (delta K sub th) to the mid-range of stress intensity in HY80 and HY130. It was hoped that such a study would lead to an improvement in fatigue properties of HY80 and HY130 as well as a better understanding of how fatigue crack propagation is related to microstructure. While there is little theory for (delta K sub th), the mid-region of delta K is relatively well understood. In previous research in this laboratory, the plastic work required to propagate a unit area of fatigue U was shown to be an important parameter for controlling the rate of fatigue crack propagation; da/dN is inversely proportional to crack U. A technique was developed for measuring U by cementing foil strain gages ahead of propagating fatigue cracks and mapping the local plastic work over the plastic zone at the crack tip.