Thermal-mechanical behaviors of dual-phase steel sheet under warm-forming conditions

This paper examined the thermal-mechanical behaviors of the given dual-phase (DP) steel sheet at warm-forming temperatures (20-190 °C). The dynamic strain aging effect of the given material was observed via thermal-uniaxial tensile tests and the temperature-dependent flow stress function was then established. Moreover, the biaxial tensile tests at series of elevated temperatures were also carried out and the corresponding experimental yield loci were then determined by utilizing the concept of plastic work contour. For the convenience of characterizing the thermal-mechanical yielding behaviors of the given material, a temperature-dependent Yld2000-2d yield criterion was proposed in this work, of which the exponent and anisotropic parameters were replaced by the nonlinear fitting functions expressed in terms of temperature. Afterwards, the proposed model, together with other existed constitutive models, were programmed as user subroutines VUMAT in ABAQUS with 'NICE' explicit integration algorithms. The cylindrical deep drawing tests under warm forming conditions and corresponding FEM simulations were then conducted to assess the precision of the proposed model.