Forming Limits of Anisotropic Sheets with Non-Power-Law Hardening

For aluminum alloys and some advanced high-strength steels, the tensile flow curve exhibits a tendency to saturate. The suitability of constitutive equations was analyzed for aluminum 6111-T4 and a general non-power-law hardening model was adopted in the derivation of forming limits incorporated material anisotropy with varying R-values. A bifurcation analysis was conducted for the left-hand-side FLD under the assumption of proportional loading and zero-extension necking orientation. Analytical results showed good correlation with Nakajima forming limit test data for aluminum sheets following Voce hardening law.