Experimental study of the distribution of plastic strains near a crack tip during static loading

Abstract

Solutions have now been obtained for a significant number of problems in linear and nonlinear fracture mechanics. These solutions have been used to devise fracture criteria for experimental evaluation of the fracture toughness of structural materials - such evaluations being necessary to substantiate the selection of materials for products. However, existing fracture criteria in general and the criteria for the elastoplastic region in particular do not adequately describe the damage that actually occurs in this region. There has been very little study of the processes that take place in the plastic zone ahead of the crack tip in elastoplastic materials. No definitive answers have yet been obtained to questions regarding the dimensions, shape, and stress-strain state of the plastic zone near the crack tip and structural changes within this region. To a large extent, these are the very factors that determine the kinetics of crack propagation. At the same time, developing valid crack models and fracture criteria remains an important problem in fracture mechanics. In this article, we report results of an experimental study of the evolution of the plastic zone on the surface of specimens near a crack tip as the crack opens during static loading: estimates are mademore » of the level and character of distribution of the strains and the structural changes that occur.« less