Analysis of Multi-Stage Deformation within the Warm-Forming Temperature Range

Abstract

In many warm-forming processes the workpiece is deformed in a number of stages, with short time intervals between each step. The yield stress depends then upon the strain history, and it is influenced by strain hardening, static and dynamic strain ageing, recovery and, possibly, recrystallization. In the present paper constitutive relations are proposed, in which those phenomena are taken into account. The influence of the incremental deformation on the yield stress is theoretically analysed. Also the process of strain localization is studied, taking as an example a nonhomogeneous specimem subjected to tension. It is found, that the strain localization process may be delayed or accelerated depending on the holding time and the strain increments. Under favourable conditions the limit strain may be essentially increased by the multi-stage deformation.