A numerical method to predict the rate-sensitive hardening behaviour of sheet materials using uniaxial and biaxial flow curves

Abstract

The use of advanced high strength steel (AHSS) is increasing in the automotive industry due to their remarkable strength-to-weight ratio and formability. In recent years, there has been a keen interest to employ high-energy rate forming processes such as electromagnetic and electrohydraulic forming because they can significantly improve the formability of these materials. However, simulating these forming processes requires reliable hardening functions that can accurately predict their flow behaviour in a wide range of strains and strain rates. One of the limitations of uniaxial tension tests is that the maximum uniform strain is not sufficient to calibrate a hardening function at high strain levels. In this work, a new numerical method is proposed to generate the extended flow curves of DP600 and TRIP780 from uniaxial tension data obtained at strain rates ranging from 0.001s-1 to 1000s-1 and from balanced biaxial tension data obtained under quasi-static conditions. Then, a 7-parameter strain-rate dependent Voce hardening function, which accounts for stage IV hardening, was fitted to the true stress-strain curves thus generated. Finally, statistical analysis was used to evaluate the goodness of the fit of predicted results.