Analysis of fatigue crack growth under compression–compression loading

It has been suggested that two driving forces ΔK and Kmax mainly govern the overall fatigue crack growth behavior of any material. This basic concept has been used to explain the damage in the tension–tension and tension–compression regime in a self-consistent manner. In the present paper, this concept has been extended to analyze the compression–compression fatigue behavior. The analysis indicates that to characterize accurately the entire crack growth region of loading from R<0 to R>0, one must include both the internal stresses and the applied stresses. It is observed that there is an unique internal stress gradient that can be represented for the entire regime of crack growth. The basic criteria for a crack advance would then be the total driving force of both ΔK and Kmax has to exceed their corresponding threshold values for a long crack. In certain cases, there can be a deviation from this uniqueness of the internal stress gradient due to additional contribution from plasticity.