Springback Predictions of a Dual-phase Steel Considering Elasticity Evolution in Stamping Process

Mechanical properties of a dual-phase steel of 0.8 mm thickness are investigated with uniaxial tensile loadings at room temperature. Standard tensile tests are conducted to determine Young's modulus, flow curves and plastic strain ratios in rolling, transverse and diagonal directions, respectively. Moreover, uniaxial tensile loadings with unloading-reloading cycles are performed to determine the elastic modulus evolution. Anisotropy of DP600 steel is described using isotopic hardening plasticity in junction with Hill's orthotropic yield function and applied in finite element (FE) stamping analysis of an automotive structural member. In sheet metal deformation modeling, material models with both constant and variable Young's moduli were considered to assess the effect of stiffness degradation on FE springback predictions. Effective plastic strain and part thickness distributions calculated with both models were fairly similar and maximum differences were determined to be 4 and 6 %, respectively. A similar situation holds for predicted springback distributions, but springback magnitudes calculated with variable modulus model were constantly higher. Computed geometries with both FE models were, furthermore, evaluated with surface scanning of manufactured parts. While stamping geometries predicted with both models underestimate actual shape distortions determined in manufactured parts, calculations with variable modulus have reduced maximum geometric deviation by 20 % and constantly improved shape correlation.