The validity of mathematical models evaluated by two-specimen method under the unknown coefficient of friction and flow stress

A modified two-specimen method (MTSM) has been derived from an objective function of two-specimen according to the inverse method. Its principle is that the flow stress for a given material is specimen geometry-independent, while the flow resistance depends on it. This method not only can evaluate the validity of a selected mathematical model when both the coefficient of friction and the flow stress are unknown for a given process, but also it can estimate the on-line coefficient of friction and flow stress when the mathematical model selected is valid. The method has been verified by experiments of cylinder, Rastegaev specimen upsetting and plane strain compression test with an annealed aluminum alloy AA6082 (Al-Si1Mg0.9Mn0.1). The flow stress and the coefficient of friction obtained from the method have been examined by finite element method (FEM) simulations and the ring test as well.