Constitutive models of plasticity for anisotropic sheet metals for cold/warm forming and their forming simulation applications

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This work deals with the constitutive modeling of plasticity and its application to sheet metal forming simulations. The summary of the research results is as follows :[1] Constitutive modeling(1) A constitutive model of large-strain cyclic plasticity, which properly describes the Bauschinger effect and cyclic hardening characteristics, as well as the anisotropy of sheet metals, Yoshida-Uemori model, has been proposed. This model has been verified by comparing the simulated results with the corresponding experimental results for deformation behavior in cyclic plasticity and bi-axial stretching tests.(2) A model to describe the yield-point phenomena of annealed steels has been proposed.(3) The effects of temperature and strain rates on the visco-plastic behavior of an aluminum alloy (A5083) and a magnesium alloy (AZ31) sheets were experimentally investigated. Based on the experimental observations, constitutive models of visco-plasticity have been presented.[2] Numerical simulations and process design for sheet metal forming(1) The above Yoshida-Uemori model has been implemented to a commercial FE code of PAM-STAMP, and using this, FE simulations of a hat-type draw-bending and S-rail forming were performed. From the results, it was found that the predictions of sheet draw-in and springback by this his model are more accurate than those calculated by a conventional model of the isotropic hardening plasticity.(2) A new algorithm for springback analysis taking account of the elastic deformations of dies has been proposed.(3) A method of springback control by optimum drawbead setting has been presented.(4) A criterion for fracture limits of sheet metals under stretch bending has been proposed.(5) Formability of adhesively-bonded sheet metals has been investigated by performing experiments and numerical simulations.(6) A new technology of incremental sheet-metal forming with local heating has been proposed.