An analytical model of plasticity induced crack closure

Abstract

Accurate and non-conservative measurements of fatigue crack growth rate are essential when designing efficient structures to be subjected to cyclic loading. Crack closure is a main mechanism of fatigue crack propagation and must be included. Numerical models have been successfully developed to predict plasticity induced crack closure (PICC), however a full understanding of the links between physical parameters, residual plastic wake and PICC has not been achieved yet. The objective of the present paper is the identification of the main micromechanisms involved in PICC and the establishment of qualitative and quantitative links between plastic deformation and the level of PICC. An M(T) specimen with 200×60×0.2 mm3 and an initial crack of 10 mm was studied. It was found that the linear superposition applies to the effect of individual plastic wedges on the PICC level. The vertical elongation of the plastic wedge, Δy, was considered and found adequate to quantify the weight of individual plastic wedges in the residual plastic wake. The effect of an individual plastic wedge was found to have an exponential decrease with the distance to the crack tip, d. An empirical model was developed relating the PICC level of individual plastic wedges with the distance d and the plastic deformation level, Δy, and was applied successfully to predict PICC evolution from residual plastic wakes.