Dynamic yielding and plastic flow behavior of Ti-6Al-4V under complex loading

The mechanical properties of metallic materials under complex loading at high strain rates are very important for material processing and engineering design. In this paper, a newly developed electromagnetic Hopkinson bar system is used to conduct dynamic experiments on Ti-6Al-4V titanium alloy under tension/compression-torsion loading conditions. The dynamic plastic behavior of the alloy, subject to complex stress states, was investigated at different loading rates under tension–torsion and compression-torsion conditions. A dynamic asymmetry yield criterion (DAYC) and loading surface (DALS) with different loading paths were proposed. The coupling effects of strain rate and stress state were considered in the yield and hardening functions. The results reveal non-uniformity in the initial yield surface and the expansion of loading surfaces at different stress states under high strain rates. Through comparison with experimental results, the reliability and accuracy of the proposed yield criterion and loading surface were validated. At last, a study on the direction of plastic flow was conducted, which demonstrated that the associated flow rule was basically satisfied.