Modeling the Strain Hardening of Porous and Powder Materials During Pressing

Abstract

Strain hardening during pressing of powder compacts is commonly described by evaluating the average strain rate intensity. Such data allow predicting the evolution of the average yield stress of powder particles considering the strain hardening of compact material. The accuracy of this approach is assessed by comparing the values of compacting pressure determined by evaluating the average yield stress and by numerically modeling the deformation of representative cells of a porous material. Determining strain hardening from the average strain rate intensity gives a qualitatively correct description of the variation in the compacting pressure. Quantitative differences are observed only at the beginning and at the end of the pressing process, when the strain rate distribution over powder particles becomes sharply nonuniform. Evaluation of the strain hardening of a porous sample is hardly effective without detailed data on the macroscopic yield behavior of powder during pressing. This shortcoming can be avoided by evaluating strain hardening using direct multiscale modeling, which does not require macroscopic constitutive equations in analytical form. The effect of strain hardening on the residual tensile stresses in a synchronizer ring is considered as an example. It is shown that high tensile stresses are responsible for cracks in the blank.