Inverse analysis applied to the evaluation of material parameters in the history dependent flow stress equation in hot forming of metals

Abstract

The paper deals with the problem of the description of the flow stress in the finite element programs for the hot forming processes. Two aspects of the problem are considered. First is the fact that the flow stress function in the finite element codes is used for the local, current values of the temperatures, strain rates and strains, therefore, this function should not be determined directly from the measurements of the compression stress in the plastometric tests. Application of the inverse technique is suggested here to avoid the problems with the interpretation of the tests. This technique allows to avoid the disturbances introduced by deformation heating, friction and inhomogeneity of deformation and to determine the stress-strain function which can be used for the description of current local properties in the finite-element programs. An introduction of the history dependence in the flow stress function was the second aspect of the project. It was achieved by the integral term in the yield stress equation. The method appeared to be efficient for the simulation of dynamic recrystallization. Further investigation should include modelling the dynamic recovery in the same way.