Prediction of Fracture in Plate Forging.

Abstract

Ductile fracture in plate forging is analyzed. For the prediction of the fracture the criterion based on load instability is employed. The concept of load instability corresponds to the loss of load control which arises when the load deforming a material is imposed over the strength of the material and is brought as the stationary state of largest nominal stress component, s^^·1=0. This gives basic condition of load instability. When the basic condition is satisfied, in order to realize the occurrence of cracking the co-existence of plastic loading and unloading must be required, which gives the annexed condition of load instability represented as z^-L≤0. Hence, the criterion is composed of basic and annexed conditions. Stress and strain in a specimen are evaluated using FEM. The index z^-L is examined at s^^·1=0, and is obtained at a number of working conditions designating tool radius and friction coefficient between tools and a plate. These working conditions are divided into two regions according to the sign of z^-L. When z^-L is negative at a working condition the fracture is predicted in such working. It is found that load instability predicts cracking possibility lower than plastic instability.