Calibration of Distortional Plasticity Framework and Application to U-draw Bending Simulations

Abstract

A new version of a distortional plasticity framework, the so-called homogeneous anisotropic hardening (HAH), was investigated regarding its calibration and its application to the numerical analysis of the U-draw bend test. First, the mechanical properties of a dual-phase steel sheet sample, DP780, were characterized using uniaxial tension, bulge and elastic loading-unloading tests to provide the data for the calibration of a conventional constitutive description assuming isotropic hardening. Then, tension-compression with different load reversal numbers and two-step tension tests were performed to produce strain path changes that lead to anisotropic hardening effects. The coefficients of this new model, called HAH₂₀, were determined with an optimization procedure. Several sets of coefficients were identified depending on the number of reversals considered in tension-compression. U-draw bend test simulations were also carried out to validate the HAH₂₀ model and its implementation in a finite element code, to compare the results with an older version of the HAH model family, and to assess the influence of the input data used in the coefficient calibration. In addition, the influence of the cross-loading effect on the U-draw bending predictions was examined. The main conclusion of this work is that the HAH₂₀ coefficients calibrated for the description of reverse loading depend on the number of reversals during the tension-compression tests. The results of the U-draw bending simulations indicate that this dependence may lead to significant differences in the predicted amounts of springback.