Parameters Determination of Yoshida Uemori Model Through Optimization Process of Cyclic Tension-Compression Test and V-Bending Springback

Abstract

In recent years, the studies on the enhancement of the prediction capability of the sheet metal forming simulations have increased remarkably. Among the used models in the finite element simulations, the yield criteria and hardening models have a great importance for the prediction of the formability and springback. The required model parameters are determined by using the several test results, i.e. tensile, compression, biaxial stretching tests (bulge test) and cyclic tests (tension-compression). In this study, the Yoshida-Uemori (combined isotropic and kinematic) hardening model is used to determine the performance of the springback prediction. The model parameters are determined by the optimization processes of the cyclic test by finite element simulations. However, in the study besides the cyclic tests, the model parameters are also evaluated by the optimization process of both cyclic and V-die bending simulations. The springback angle predictions with the model parameters obtained by the optimization of both cyclic and V-die bending simulations are found to mimic the experimental results in a better way than those obtained from only cyclic tests. However, the cyclic simulation results are found to be close enough to the experimental results. sheet materials have anisotropic behaviors due to the rolling operation and crystal structures, the use of anisotropic yield functions in the simulations increases the accuracy of the prediction. In addition to the used anisotropic yield criterion functions, the hardening model parameters (i.e. isotropic, kinematic and combined isotropic-kinematic hardening) are also important effective parameters for the accuracy of the simulation results. Particularly, the kinematic and combined isotropic-kinematic hardening models are important for the forming simulation of the most of aluminum alloys as well as advanced high strength steels (TRIP "Transformation Induced Plasticity", TWIP "Twining Induced Plasticity", and DP "Dual Phase" steels) which have a high tendency to springback due to the relatively high yield strength they show. Recently, the prediction of the formability and springback characteristics of these materials have been shown to be enhanced by using the cyclic plasticity models in which the different deformation combinations like tensioncompression are well defined (Uemori et al., 1998(Uemori et al., , 2000. In the real stamping operations of sheet metals, some specific regions are generally exposed to different deformation path during the flowing through the die cavity. The main problem in a classical modelling (isotropic) approach is the assumption of the same mechanical responses under different loading conditions. However, most of the sheet materials behavior under forward and reverse loading directions is not the same and the difference between these loading conditions is called as Bauschinger effect. The Bauschinger effect is mainly addressed to the early yielding of the metals when the loading direction is reversed.The contribution of the Bauschinge...

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