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Modelling the plastic anisotropy evolution of AA5754-H22 sheet and implementation in predicting cylindrical cup drawing process

In this paper, constitutive models for sheet metals that take into account evolution of plastic anisotropy during material forming are developed and analyzed considering experimental data for aluminum alloy 5754-H22 sheet. The developed models are based on associated or non-associated flow rule approach and utilize simple four parametric orthotropic stress functions, quadratic Hill-48 function or non-quadratic Karafillis-Boyce function. An experimental study is performed in order to characterize the plastic anisotropy and its evolution with straining in tensile testing for the considered material. Lankford coefficient (r-value) is calculated as an instantaneous value based on the polynomial fit of the transverse versus longitudinal true plastic strain diagram. The directional dependences of yield stress ratios and instantaneous Lankford coefficients corresponding to the selected amounts of plastic work are determined. Based on the obtained data, anisotropy parameters of Hill-48 and Karafillis-Boyce stress functions are set as the polynomial functions of the equivalent plastic strain. The developed models based on associated or non-associated flow rule and Hill-48 or Karafillis-Boyce stress function with variable anisotropy parameters are analyzed in predicting the cylindrical cup drawing process for the considered material. The implicit algorithmic formulations of the analyzed constitutive descriptions are implemented into the finite element program ADINA 8.6 via user defined subroutine CUSERG. The predictions of cup drawing process are compared with the experimental data. The results demonstrate that the evolving plasticity model based on non-associated flow rule and non-quadratic Karafillis-Boyce stress function provides the best estimation of the earing profile. Based on the obtained results, the influence of plastic anisotropy evolution description on the cup drawing predictions is assessed.

plastic anisotropy evolution ; non-associated flow rule ; sheet metals ; constitutive modelling ; cylindrical cup drawing

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