A constitutive model for finite deformation of endochronic plasticity in powder forming processes

In this paper, an endochronic constitutive model is developed for cold powder compaction processes. As large deformations are observed in powder forming processes, the endochronic constitutive model based on large strain plasticity is presented and an integration scheme for the rate constitutive equations is established. Although the concept of yield surface has not been explicitly assumed in the endochronic theory, it is demonstrated that the cone-cap yield surface can be derived as a special case of the proposed endochronic model. The plastic flow rule and the dilatancy condition of the model are derived and a procedure for calibration of material parameters of the constitutive model is proposed. The material parameters in the endochronic model are calibrated for MH-100 iron powder to reproduce experimental data and the predictive capability of the model is assessed by simulating a powder compaction process.