Numerical study of fatigue crack growth considering an elastic–plastic layer in mixed-mode loading

In this work, crack propagation simulations in a weak surface between an elastic–plastic layer and an elastic substrate are considered. A plane strain model is used in the simulations. Fracture propagation process is taken into account by an irreversible cyclic cohesive zone model. Loading applied to the structure is rotated in order that mixed loading modes could be introduced. Besides loading, thickness of the elastic–plastic layer is also changed. All other intrinsic fracture properties are kept constant. The present work shows a direct relation between mode II applied energy and the energy dissipated plastically during propagation. As a consequence, the introduction of mode II loading intensifies the effects of the elastic–plastic layer, resulting substantially larger plastic strains, more extensive crack closure during unloading and smaller tractions at the crack tip when the size of the layer increases. The result is a substantial increase in the fatigue crack growth resistance. These effects are minimal or not observed when only mode I is considered.