Application of Different Hill’s Yield Criteria to Predict Limit Strains for Aerospace Titanium and Aluminum Sheet Alloys

More recently, Titanium and aluminum alloys are gaining more interests to be implemented in hydro-forming applications. It is necessary to predict forming limits for these sheet alloys. Forming limits play an important role in metal forming processes. Forming limit diagrams, present the limit strains for various linear strain paths. In other hand, forming limit curve (FLC), illustrates localized formability for sheet metals under proportional loadings and are known as a powerful tool for trouble-shooting in sheet metal forming processes. In this study, mechanical properties of Ti-۶Al-۴V titanium sheets, AA۷۰۷۵-T۶ and AA۲۰۲۴-T۳ aluminum sheets are investigated through the uni-axial tensile test. Anisotropy coefficients as well as work-hardening exponent resulted from tensile test were used to theoretically prediction and numerical simulations of limit strains. For the theoretical prediction of the forming limit curves, several constitutive models were implemented. Several Hill’s yield criteria combined with Swift equation and empirical equation proposed by NADDRG were accomplished to predict the FLDs. Results showed that calculated numerical results are in good agreement with the predicted theoretical data when Hill۹۳-Swift is the instability criteria used.