The mechanical response of commercially pure copper under multiaxial loading at low and high strain rates

•A novel Tension-Torsion Hopkinson bar was developed.•The dynamic tensile-shear failure envelope of commercially pure copper is studied.•The high-rate loading paths show proportional direct and shear strain.•The Drucker-Prager criterion approximates the failure stress envelope.•The failure stress locus indicates rate dependence from low to high strain rates.