Multi-axial deformation behavior and its constitutive equations for superplastic materials

摘要

Superplasticity of polycrystalline metallic material is the phenomenon of large plastic deformation (for example, up to hundreds percents, or thousands percents) without necking under uniaxial tensile loading. Such phenomenon happens in the fine-grain metallic material whose main deformation mechanism is a grain boundary sliding, under some limited loading conditions, for example, low strain rate and elevated temperature. This phenomenon is expected as a new forming technology in the engineering/industrial field. Authors have been investigating the superplastic deformation under the general thermo-mechanical loading condition applying the combined loads of axial force and torque to the thin-walled tube specimen made of typical so-called superplastic materials 5083Al alloy and Zn-22%Al alloy. In the result, several unique deformation phenomena were observed. In this paper, a set of general constitutive equations is proposed on the basis of mathematical (phenomenological, potential) theory of plasticity.