A Crack Initiation Model in High Cycle Fatigue of Low-Carbon Steel

Abstract

The fatigue lives of metals up to crack initiation have been investigated with a stochastic model based on accumulation of fatigue damage. In the model, it is assumed that the fatigue damage is accumulated randomly inside the metal in the form of dislocations under the repeated stress and that a microscopic crack occurs when the strain energy due to local piling-up of dislocations exceeds a specific value. The size of the initiated crack is on the order of microscopic structure (cell) corresponding to the scale of dislocation piling. The cell size is determined from probabilistic arguments. The growing process from a cell-sized crack to a grain-sized one is treated with some assumptions. Our theoretical results are compared with the experiments using three kinds of low carbon steel S20C with different grain sizes, and the consistency of the model is examined.