Modeling of Strain Hardening in Porous and Powder Materials during Pressing

Abstract

Strain hardening during powder pressing is commonly modeled through evaluation of the mean strain rate intensities. These data allow predicting the evolution of mean yield stresses of powder particles using relationships for strain hardening of the respective compact material. The accuracy of this approach is assessed by comparing the compacting pressure determined by the mean yield stresses and that obtained by numerical simulation of strains for representative cells of the porous material. Strain hardening determined with the mean strain rate intensity gives qualitatively correct description of variation in compacting pressure. Quantitative differences are observed only at the beginning and at the end of the pressing process, when strain rate nonuniformities in powder particles are very sharp. At the same time, evaluation of strain hardening of the porous sample is hardly possible without detailed data on macroscopic yield behavior of the powder during pressing. This shortcoming can be avoided if direct multiscale modeling is applied to evaluate strain hardening. This numerical approach does not use macroscopic constitutive equations in analytical form. The effect of strain hardening on residual tensile stresses in a synchro hum sample is considered as an example. It is shown that high tensile stresses lead to cracks in the sample.