engleski

Evolutionary Anisotropic Plasticity Models for Sheet Metals

Sheet metals exhibit initial plastic anisotropy mainly caused by the production rolling steps. Anisotropy is closely related to the formability of material and should be considered carefully for the accurate analysis of sheet metal forming processes. The phenomenological anisotropic plasticity models for sheet metals are mostly calibrated based on the initial yield stresses and constant Lankford coefficients obtained in uniaxial tensile tests of sheet specimens with different alignment to the rolling direction. Some recent experimental studies demonstrate that the yield stress ratios and instantaneous Lankford coefficients evolve with ongoing plastic deformation in uniaxial tensile tests. These observations indicate that besides initial anisotropy, sheet metals exhibit deformation induced anisotropy, that is plastic anisotropy in sheet materials evolves with continuation of plastic deformation in forming process. The objectives of this research are oriented towards development of phenomenological plasticity models capable to describe plastic anisotropy evolution in sheet metals and their evaluation in predicting complex sheet metal forming processes. In the present study, phenomenological evolutionary anisotropic elasto-plastic constitutive models for sheet metals based on the isotropic-distortional hardening concept and associated or non-associated flow rule are developed and analysed. The developed models utilize Hill-48, Karafillis-Boyce or Yld2000-2d stress function as yield function/plastic potential. For the selected sheet material, capabilities of the analysed stress functions in predicting evolution of directional dependences of the uniaxial tensile data with ongoing deformation are presented. Some aspects related to the calculation of Yld2000-2d function anisotropy parameters are considered. In the developed constitutive formulations, anisotropy parameters of the yield function/plastic potential are stated as continuous functions of the equivalent plastic strain as the hardening parameter. The algorithmic formulations of the considered constitutive models based on the implicit return mapping algorithm are developed and implemented into the finite element code ADINA. The developed formulations are analysed in predicting the cylindrical cup deep drawing process for the considered material.

plasticity, sheet metals, evolving anisotropy, cylindrical cup deep drawing

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