The inclusion of compressive residual stress effects in crack growth modelling

Compressive residual stresses are often deliberately induced at holes and notches to improve the fatigue performance of parts with these features. A modification to the FASTRAN II deterministic life prediction model was developed to account for the presence of compressive residual stresses. They were accounted for by replacing the opening stress as the closure mechanism with a closure mechanism consisting of the compressive residual stress and a reduced opening stress. An experimental program was developed to investigate the effects of residual stresses on fatigue lives. Compressive residual stresses were induced in the notches of 2024-T3 aluminium single-edge notch tension [SE(T)] specimens using tensile overloads. The residual stress distributions were depicted by finite element analyses. Four sets of specimens, each subjected to a different overload level, were tested under constant amplitude loading. Because of the variability observed in experimental fatigue lives, a probabilistic approach was used to predict the distribution of fatigue lives of the SE(T) specimens with compressive residual stresses. The variability of the experimental fatigue lives for the SE(T) specimens was predicted using the residual stresses, measured particle distributions for the material, a modified version of FASTRAN II, and conditional probability. The predicted fatigue life distributions for the four residual stress levels examined agreed with the experimental data with average errors between 5 and 15%.