Analytical estimation of asperity-induced crack closure

Abstract

The concept of crack closure has been used for over twenty years to explain the characteristics of fatigue crack growth. It is generally accepted that crack closure reduces the applied stress intensity amplitude, and is particularly significant at the near threshold regimes. The asperity-induced crack closure has been considered as one of the main closure mechanisms, since roughness-induced and oxide-induced closures can be treated as special cases of it. Vasudevan, Sadananda and Louat have reviewed crack closure effects and concluded that the closure effect is much less than that usually believed. They argued that the asperity-induced closure was only about one quarter of that computed from the slope change point on load-displacement curves. The argument was based on their theoretical evaluation using a dislocation crack model in which a sharp asperity was located near the crack tip. Note that Louat et al. have only evaluated an extreme case in which the asperity width can be ignored. In this work, the authors evaluate the crack closure when the asperity thickness varies from a point to finite values, in order to obtain more realistic estimation of asperity-induced closure during fatigue crack propagation.