Finite element analysis of plasticity-induced fatigue crack closure

Abstract

Contact elements are implemented into the elastic-plastic finite element analysis of fatigue crack closure to predict crack opening stress, by developing a code using ANSYS Parametric Design Language. Although the use of contact elements in modeling crack surface contact is inherently natural, almost no effort to incorporate them has been reported in the literature. The traditional method is based on placing truss elements on the crack surface nodes. The load is applied incrementally, during which the crack surface nodes are monitored to predict crack opening stress values. In this research contact elements are used to model crack surface contact and the determination of crack opening stress is accomplished by monitoring the state of contact elements during incrementally applied loading. The results of two dimensional finite element analyses are in good agreement with previous work given in the literature. Instead of determining crack opening stress of every load cycle, an algorithm that makes it possible to find crack opening stress at predetermined load cycle intervals is developed. With the developed algorithm it was possible to analyze crack closure behavior during a larger number of load cycles with less execution time. The newly introduced parameters such as effect of the number increments of the applied load, the effect of the load cycle interval where the opening stress values are determined are investigated. Due to simulation of relatively high number of load cycles, final stabilization of crack opening stress values after a subsequent decay in the initially “stabilized” opening stress values is observed.