Formability analysis of pre strained AA5754 O sheet metal using Yld96 plasticity theory role of amount and direction of uni axial pre strain
Automotive industries are very much interested in formability of different pre strained aluminum alloy sheets in the context of multistage stamping to fabricate complex components. In the present work, different uni axial pre strains of 6.4% and 12.2% were induced in AA5754 O aluminum alloy both along rolling direction (RD) and transverse direction (TD) The true stress strain response, limiting dome height (LDH) and strain based forming limit diagram (e FLD) of as received and all pre strained materials were evaluated experimentally. The anisotropy constitutive material model was developed using the Yld96 plasticity theory in conjunction with the Hollomon isotropic hardening law to predict the yield strength evolution of the pre strained materials. Also, it was found that the limiting strains in e FLD shifted significantly depending on the amount and direction of uni axial pre strain. Hence, the limiting strains of the as received materials were transposed into stress space to estimate the stress based forming limit diagram (s FLD) using the anisotropy constitutive material model. Further, the dynamic shifts of e FLDs of four different pre strained materials were predicted by successfully decoupling the s FLD of as received materials within root mean square error of 0.008. Finite element models of both uni axial pre straining and subsequent LDH tests were developed, and the forming behavior of the pre strained materials were predicted implementing the Yld96 plasticity model and estimated s FLD. It was found that LDH was significantly influenced by the amount of pre strain, and the maximum thinning location shifted close to pole in the case of 12.2% pre strained materials. However, the effect of uni axial pre strain direction on both LDH and maximum thinning location in AA5754 O material was very negligible.