Failure at and Near Interfaces.

Abstract

Abstract : This report covers results of research addressing the failure behavior of bonded materials at and near the interface in support of structural integrity methodology of the failure response of solid propellant rocket motors under storage and operating conditions. Interfacial failure has been investigated both experimentally and analytically. Experiments determined the propagation of a crack away from an interface and established the direction and onset of crack propagation. The analytical studies corroborated this behavior essentially very well, except that the small deformation analysis was found to be devoid of uniqueness, in that a size parameter is needed to closely correlate the experiments with the analysis. As a result detailed large deformation analyses were also performed that eliminate much of the uniqueness problem, but leads to crack propagation in one direction only. It is concluded that a true fracture problem is a mix between small and large deformation formulations. These formulations depend on how large the growth steps of crack propagation are relative to the size of a small zone of nonlinear material response around the crack tip vis-a-vis the region of relatively small Strain farther from the crack tip.