Elastic-plastic analysis of frictionless contact at interfacial crack tips

Abstract

The asymptotic elastic behavior of an interfacial crack occurring between two dissimilar isotropic media is reviewed. Distinct solutions, based on differing assumptions regarding crack-face boundary conditions, can be generated. The assumption of traction-free faces generally leads to oscillatory singular asymptotic fields which mathematically cause crack-face interpenetration, an inconsistency which can be alleviated by alternatively assuming asymptotic frictionless contact. For predominant tensile loading, the elastically-calculated ratio of contact length to crack size is typically very small, but may become appreciable when shear loading is applied. In either case, the singular crack-tip stresses cannot be sustained in materials capable of limited plastic flow, and small scale yielding (SSY) should be considered. In an extension of previous work [11], we identify conditions for SSY within surrounding dominant elastic regions of both traction-free and frictionless contact types. For the latter case, approximate closed form expressions for the plastic zone size and shape are obtained as the locus of points where the elastically-calculated Mises stress equals the tensile yield strength, σ _ys ,. The maximum extent of this plastic zone is approximately 3K ^c2_II /2σ ² _ys , where K ^c_II , is the closed crack-tip bimaterial stress intensity factor. Precise SSY numerical calculations for an elastic/perfectly-plastic material atop a rigid substrate indicate that the asymptotic stress field in the plastically-deforming material is composed of two fan regions and two constant state regions. Within the plastic zone, the interfacial and crack-face tractions asymptotically reach constant values. Compressive crack-face tractions persist even when contained inelastic crack-tip deformation is included.