A Modified Johnson–Cook Model for Modeling AA6061-T6 under Different Temperatures Considering Ductile Fracture

An accurate constitutive model is a prerequisite for formability simulation analysis. In the study, the mechanical properties of AA6061-T6 at 20-450 °C conditions was investigated. The original Johnson–Cook (J–C) model was not suitable for predicting the flow behavior over the wide range of temperature. A modified segmented J–C model was proposed and aimed to accurately reflect the trend of flow stress–strain at various temperature. To improve the prediction accuracy of the constitutive model, the model parameters were calibrated using a genetic algorithm. The damage values of Ayada criterion were calculated at different temperatures and fitted with an exponential function. Subsequently, the segmented J–C model and modified Ayada criterion were written in the VUMAT subroutine to simulate the quasi-static uniaxial tension of AA6061-T6 at elevated temperature. The results indicated that there was a significant difference in the flow behavior of AA6061-T6 below 300 and above 300 °C. The modified segmented J–C model could better predict the flow stress of AA6061-T6 at various temperatures and the genetic algorithm could effectively improve the fitting accuracy compared to the traditional fitting method. The simulation results showed that the modified Ayada criterion could predict the AA6061-T6 ductile fracture at elevated temperature. It further proved that the accuracy of the segmented J–C model and modified Ayada criterion.