Ductile fracture in pure silver under high-triaxial stresses

Abstract

The purpose of this study was to determine the mechanism of ductile fracture in pure silver subjected to a triaxial stress state. This was accomplished by preparing mechanical-testing specimens of thin, constrained, silver interlayers. The general objective of this research was to determine the (perhaps common) mechanism for ductile fracture in materials subjected to a variety of triaxial stress states. The approach consisted of three tasks: first, the authors compared the Huang et al. numerically determined instability criterion for an axisymmetric principal stress state with the experimentally observed [sigma][sub m]/[sigma][sub y] values for simple, tensile-loaded, high-purity, silver interlayers at failure. This would determine whether the unstable cavity growth mechanisms can apply to the important case of low strain ductile failures in thin constrained interlayers loaded in tension. Second, they would experimentally examine (ductile) fractures under other triaxial stress states, such as axisymmetric and non-axisymmetric stress-states, apparently outside the HHT predicted limits of unstable cavity growth in elastic-perfectly plastic solids with [sigma][sub 2]/[sigma][sub 1] < 0.75 (for [sigma][sub y]/E [approx equal] 0.003). This would be followed by an analysis of the failure, particularly for the case of small macroscopic plastic strains to failure. This would include comparing the observed stress statesmore » associated with ductile failure in biaxially loaded interlayers with FEM predictions of the stress levels required for unstable cavity growth using identical stress states (i.e., [sigma][sub 1], [sigma][sub 2], and [sigma][sub 3] of the same ratios).« less