Interface Crack Propagation between a Porous-Ductile Material and a Rigid Substrate

Along the interfaces between ductile and brittle materials a slow, stable crack growth is often observed before the crack propagates into one of the two materials. In the present work, a numerical asymptotic solution is provided for the stress and velocity fields near the tip of an interface crack, steadily propagating between a porous elastic-plastic material and a rigid substrate, under plane strain conditions. The Gurson model with constant and uniform porosity distribution and isotropic hardening is assumed for the constitutive description of the ductile material. This model may accurately describe the behavior of incompletely sintered porous metals and particulate-reinforced metal matrix composites. In analogy with the problem of interface crack growth in fully dense elasticplastic materials, two distinct kinds of solution can be found in variable-separable form, corresponding to predominantly tensile or shear mixed mode. These solutions exist only if the hardening coefficient is lower than a critical value. For higher values the solution may display a complex stress singularity, as for the problem of an interface crack between linear elastic materials. In any case, if the ductile material is elastically incompressible then the Dugdale parameter vanishes and variable-separable crack-tip fields can be found for every set of the material parameters.Due to the higher hydrostatic stress state, the porosity influences only the stress fields of the tensile mode significantly. In particular, for high porosities the maximum of the hoop stress deviates from the interface line ahead of the crack-tip towards the porous ductile material, causing possible kinking of the fracture, so that the toughness of the interface crack may increase significantly. Therefore, the performed analysis of debonding process of this kind of interface results to be essential for the determination of the overall strength, toughness and reliability of many advanced composite materials.