Determining crack-tip stress-field parameters from mixed-mode displacement fields

Abstract

The accurate determination of crack-tip stress-field parameters from experimentally obtained displacement patterns is often complicated by the presence of displacement fringes which are not related to the crack-tip field of interest. The main objective of this thesis is to determine if an overdeterministic, multiple-point, least-squares solution algorithm is able to accurately determine stress-field parameters from mixed-mode displacement fields, in spite of the presence of a superimposed non-symmetric, nonstrain-related displacement field. Numerical experiments, finite element analysis, and experimental data were used to demonstrate the effectiveness of the solution scheme. The ultimate goal for this solution method is to study the behavior of the cracks that can develop at interfaces in composites and ceramics after prolonged exposure to elevated temperatures and adverse environments. The local crack-tip stress field in these cases will have a Mode II component even when the global loading is purely tensile in nature.