Load path effect on fatigue crack propagation in I + II + III mixed mode conditions – Part 2: Finite element analyses

Abstract

This paper is dedicated to the analysis of the load path effect on I+II+III mixed mode fatigue crack propagation in a 316L stainless steel. Finite element analyses were conducted in mode I+II and in mode I+II+III in elastic–plastic conditions. The load paths applied in the finite elements computations were chosen so as to be equivalent with respect to most of the fatigue crack growth criteria, in particular with those based on Δkeq=(αΔKIn+βΔKIIn+γΔKIIIn)1/n since the same maximum, minimum and mean values of the stress intensity factors were used for each loading path. In addition, these load paths were chosen to be identical with those used in fatigue crack growth experiments in a 316L stainless steel. The main result of this set of analyzes is that the load path modifies very significantly the amount of plastic flow per cycle and the mode mixity of the inelastic part of the response of the cracked structure. In addition, the comparison of mixed mode I+II and mixed mode I+II+III finite element computations show that the addition of mode III loading phases to a mixed mode I+II loading cycle can increase very significantly the plastic flow in mode I+II. The finite element results are consistent with the experimental results, indicating that crack tip plasticity is at the origin of the load path effects observed in the experiments.