The yielding behavior of TU00 pure copper under impact loading

Characterizing the high strain rate behavior of metals under complex stress states has always been a challenging subject in solid mechanics. In this paper, dynamic tension-torsion tests with various stress ratios are performed by a newly developed combined tension-torsion Hopkinson bar (C-THB) system. Together with the quasi-static results, the initial yielding envelopes at different strain rates are illustrated for the first time. Tresca, von Mises and Hill yield criterion are established and evaluated. A universal model describing the strain rate hardening of material under complex stress states is proposed. Based on this model, a modified Hill yield criterion is deduced for pure copper (TU00), which fits well with the experimental yielding envelope at different strain rates.