Analytical Studies on Ductile Fracture Behavior Near the Crack-Tip

点击翻译按钮获取中文摘要

It is the purpose of the present research program to investigate analytically the deformation and fracture behavior at the crack-tip of tough-materials, to make a comparison with the experimental results, and to propose a criterion for ductile fancture at the crack-tip. Large deformation finite element analyses are performed to study deformation and microvoid concentration properties near a notch or a crack-tip under opening or mixed mode loadings with Gurson's constitutive equation used for simulating nucleation and growth of micrvoids. A macrovoid is also assumed to be located near the crack-tip in order to examine its effect on deformation and fracture behavior of crack-tip. It is shown that under mixed mode loadings one corner of a crack-tip sharpens while the other corner blunts, and the strain and void volume fraction become concentrated at the sharpened corner with the increase of mode II component. A macrovoid near the blunted corner grows rapidly and a strong interaction is evidenced with microvoid fraction concentrated at the location between the macrovoid and blunted crack corner whereas a macrovoid near the sharpened cormer is found to have little effect on crack-tip deformation and fracture properties. A generalized crack-tip opening displacement and other quantities are proposed as parameters that control onset and growth of a crack under mixed mode loadings and are compared with the experimental results. Among these parameters, the critical void fraction, the condition of shear localization, the plastic work at the crack-tip, and the generalized crack-tip opening displacement are thought to be candidates for ductile fracture criterion. Further investigations will be required bofore a definite conclusion can be drawn.