Analytical and finite element modelling of roughness induced crack closure

Crack closure is an established component of fatigue understanding, however, significant confusion remains in both experimental determination and micromechanical modelling. Analytical and finite element models of roughness induced crack closure (RICC) are developed in the present paper. A novel interpretation of RICC is explored where shear strains causing asperity contact arise explicitly from residual plastic deformation in the wake of a propagating crack, in a manner that is essentially analogous to plasticity induced crack closure (PICC). The analytical model estimates the crack opening along a simple deflected crack path, defined by a crack deflection angle and length, and residual shear at each asperity interfering with this opening to generate closure. The results from the analytical model are compared to finite element modelling and experimental results, with insight being provided into a controlling influence of the ratio of asperity size to plastic zone size on closure levels.