Modelling Fatigue Crack Growth near an Open Hole under Spectrum Loading Using a New Method for Elastic-Plastic Stress Calculation

Abstract

To date the analysis of fatigue crack growth from an open hole subjected to contained cyclic plastic deformation is problematic due to considerable computational effort involved. This paper presents the integration of a new efficient method for calculating the elastic-plastic notch stress field under cyclic loading into a crack growth analysis tool. The anticipated crack path is defined along a line emanating from an open hole, and the line is discretized into a series of elements on which the elastic-plastic stress distribution is solved for the uncracked body. This solution is then used in conjunction with a weight function approach to determine the stress intensity factors used in the crack growth analysis. This technique has been incorporated into a Defence Science and Technology Organisation proprietary crack growth analysis tool based on plasticity-induced crack closure. Results are presented for cases involving service load spectra from F/A-18 and F-111 aircraft and are compared to those obtained from a commonly used crack growth code that does not account for the effect of contained notch plasticity. It is hoped that this generic approach will lead to improved predictions for crack growth in plasticity-affected zones.