Papers by Author: Yan Wei Lu

Abstract: This paper presents a very brief overview of the philosophy underlying a plastic inclusion approach to defining the boundary stresses imposed on the applied elastic stress or displacement field by the plastic deformation attendant on crack growth in a ductile material. It leads to two new fracture mechanics parameters, KR and KS. KR defines a retardation component arising from wake contact and the Poisson’s contraction associated with the plastic zone, whilst KS describes a compatibility-induced component arising from shear at the elastic-plastic interface. These additional components imply that KF is not directly comparable with KI, as it describes the net driving force on the crack from the applied load.

Abstract: This paper presents an outline of the development, verification and application of a new model of crack tip stress fields in the presence of a plastic enclave around a growing fatigue crack. The approach taken rests on capturing the effects of this ‘plastic inclusion’, comprising the crack tip and crack wake plastic zones, via elastic stress distributions applied at the elastic-plastic boundary. The model is therefore independent of the mechanisms of plastic deformation and potentially applicable to a variety of materials. A Muskhelishvili complex potential extension to the Williams crack tip stress field is found for four stress parameters representing a K-stress, a T-stress, a crack retardation stress and a compatibility-induced shear stress at the elastic-plastic boundary. This model is validated via full field fitting to photoelastic stress fringe patterns, obtained from epoxy resin and polycarbonate specimens. It has also been extended to the strain fields measured in digital image correlation techniques, which allows its application to metallic alloys.