Anisotropy and plastic flow in the circular bulge test. (August 2017) - Reis, L.C.
Abstract: The procedures for obtaining the stress vs . strain curve from the circular bulge test are investigated in detail resorting to finite element analysis. Particular attention is given to in-plane anisotropic materials for which remains a lack of knowledge about the distributions near the pole of the bulge specimen of variables such as the surface radius of curvature, sheet thickness, principal stresses and strains as well as stress and strain paths. This study seeks to understand and evaluate the errors inherent to the commonly used experimental procedure for assessing the hardening curve from the bulge test. The procedure assumes that the stress path at the pole is equibiaxial. An empirical equation relating the stress path with the strain path at the pole of the cap is suggested to improve the determination of the biaxial stress vs. strain curve, which holds particular prominence in cases of strongly anisotropic sheets. Highlights: Stress and strain paths in circular bulge test are analysed in strong anisotropy. Errors associated with the biaxial stress vs. strain curve evaluation are quantified. Enhancement of the evaluation procedure is suggested, mainly for strong anisotropy.