Forming limit prediction using an integrated model for 7075 aluminum alloy sheets at an elevated temperature

Abstract A methodology for incorporating a ductile fracture criterion into an improved Marciniak–Kuczynski model, which extends the original works to include planar anisotropy using the Barlat89 yield criterion, is proposed to predict the forming limit diagram of AA7075. This is the most promising alloy to be introduced in the automotive industry, resulting in even greater weight reduction when compared with other alloys. Due to its poor formability at room temperature, this study is conducted at 480 °C, an elevated temperature adopted in a thermal multi-step process to form some complex parts. The integrated model is numerically solved using the Newton–Raphson method. Various ductile fracture criteria are estimated to identify the optimal theoretical model. The material constants are determined from uniaxial and equibiaxial tensile tests. To verify the model, a semispherical thickness reduction cruciform specimen is designed to achieve a fracture at the center. Further, thermal biaxial tensile testing technology, an in-plane and non-contact loading method, is adopted. Comparisons with the experimental results show that the integrated model with Oyane’s criterion achieves the optimal performance.