Finite element analysis of interfacial crack propagation based on local shear, part II—Fracture

The mechanics of fracture of a stably extending interface crack in polymeric adhesive bonds undergoing very large shear deformation is studied using a rate-del~ndent finite element analysis. Plane-strain and J2 plasticity conditions are considered. Based on recent experimental observations, it is assumed that the local engineering shear strain at a certain distance (i.e. for the polymer adhesive studied, approximately a tenth bond thickness) straight ahead of the crack tip remains constant during the crack propagation. This critical strain is rate dependent, being a function of the crack velocity. The proposed fracture criterion is applied to several experimental crack growth histories pertaining to different specimen geometries, bond thicknesses and crack velocities. Although the analysis is highly sensitive to rate effects and other material characteristics, the comparison is generally reasonably successful. The analysis also provides quantitative insight into the mechanics of other failure modes observed in the experiments. In particular, the growth of a detrimental micrndebond which is formed several bond thicknesses ahead of the crack tip seem to be controlled by the bond-normal tensile stress while hydrostatic tensile stresses appear responsible for the development of a kink or a large void at the crack tip which temporarily arrests the crack. All these and other failure modes are activated under large strains, which manifests the important rule of plasticity in the fracture of polymeric joints. © 1997 Published by Elsevier Science Ltd.