Effect of a Graded Layer on the Plastic Dissipation During Mixed-Mode Fatigue Crack Growth on Plastically Mismatched Interfaces

by Baudendistel, Craig M.

Recent work has proposed a dissipated energy theory of fatigue crack growth in lay- ered materials under mixed-mode loading. An inherent assumption of this prior work is that a perfect crack exists along the interface joining the top and bottom layers. The current work extends the approach of previous studies to incorporate a grading of plastic proper- ties between the two layers through parametric ?nite element modeling with ABAQUS. An elastic-plastic 2D model using 8-node biquadratic elements was used to map the plas- tic dissipation of a two layer specimen with a grading of plastic properties parallel to the crack face. This property gradient allows for a more realistic representation of the plastic dissipation accumulated during a steady state cracking con?guration. As a result, more ac- curate fatigue crack growth rates in layered material systems can be predicted. It was found that incorporation of a graded layer increased the amount of plastic dissipation. While this graded layer effect cannot be ignored, plastic dissipation is still dominated by the mode of loading.