Closure Behavior of Fatigue Crack

Analytical Study Based on the Simulation Results by the Extended Body Force Method

Abstract

In this paper the model of crack closure is developed to analyse the experimental results of the previous report.
The plasticity induced crack closure is simulated by leaving residual stretch in the wake of the advancing crack tip, and the roughness induced or the oxide induced crack closure is modeled by the debris whose thickness is assumed to be constant along the crack surface. The method of analysis used here is the extended body force method.
It is shown by the present model that the effective stress range ratio U_op(=1-σ_op/σ_max) or U_cl(=1-σ_cl/σ_max) of fatigue crack in the stabilized state is mainly controlled by the K_max (when stress ratio R is constant) and that the reversed crack tip opening displacement can be expressed unifyingly by the effective stress intensity range ΔK_eff^op(=K_max-K_oq) or ΔK_eff^cl(=K_max-K_cl), independently of the loading history and the stress ratio. These are in good agreement with the experimental results of the previous report. Moreover, the transitional behavior of the crack closure observed in the experiment of the previous report, when load is changed, can be illustrated as well by this model.