Computational modeling of three-dimensional mixed mode-I/II/III fatigue crack growth problems and experiments

Abstract

Mixed mode-I/II/III fatigue crack growth experiments and their simulations are performed using a system permitting all possible combinations of three-dimensional mixed mode loading conditions. The so-called Compact Tension-Shearing and Tearing (CTST) specimens used in the experiments are made of 7075-T651 aluminum alloy. Different mixed mode loading conditions are considered and the applicability of a previously developed new 3-D fracture criterion on 3-D mixed mode fatigue problems is evaluated. Crack growth surfaces obtained from numerical simulations and experiments are compared using existing criteria in the literature and the developed criterion. Especially for highly mixed mode conditions, the developed criterion predicts the crack growth surface better than the MTS criterion by reducing nearly half of the latter’s deviation from the experimental surface. Based on the computed mixed mode stress intensity factors, comparisons of lives show that most mixed mode fracture criteria underpredict fatigue crack propagation lives. Numerical analyses are also performed on a cylindrical steel bar under combined tension–torsion fatigue load to further validate the method presented. The predicted results showed good agreement with experimental data from the literature.