Characterization and assessment of anisotropic constitutive models using the flat punch hole expansion test

Abstract

Flat punch hole expansion tests are valuable for anisotropic plasticity model evaluation sine they activate a spectrum of tensile stress states across all in-plane material orientations. Pressure-independent yield functions with an associated flow rule typically overlook the state of plane strain tension (PST) during their calibration. Studies have shown that PST occurs near a principal stress ratio of 1:2 for materials that approximately follow deviatoric plasticity but this plane strain constraint (PSC) has been largely overlooked in anisotropic yield function calibration. This study proposes an efficient methodology to characterize and calibrate associated deviatoric plasticity models for materials with a broad range of anisotropy and hardening characteristics including AA5182-O and AA7075-T6 aluminum, and DC04 and 980GEN3 steels. The PST response was evaluated from notch tests using an inverse finite-element analysis approach with correlations provided when cruciform or notch test data is unavailable. The isotropic hardening assumption was evaluated to large strains by determining the stress response from analysis of area of the neck in tensile tests. The anisotropic Yld2000 and Yld2004 yield functions were calibrated to enforce the PSC, ensuring a zero plastic strain increment in directions without a deviatoric stress. The isotropic Hosford and quadratic Hill-48 functions, which universally satisfy and violate the PSC respectively, were also considered. Yield functions that enforced the PSC accurately predicted the global forces, strains, and PST locations in flat punch hole expansion simulations. In contrast, the Hill-48 model failed to accurately predict the radial distance from the hole in PST where the minor strain vanished, highlighting the importance of considering plane strain data for yield function calibration.