Dynamic large strain characterization of tantalum using shear-compression and shear-tension testing

Abstract

The dynamic large strain behavior of polycrystalline tantalum has been characterized using shear-compression and shear-tension experiments over a wide range of high strain rates (103–1041/s). Tests were carried out using the recentlymodified shear compression specimen (SCS) on a split Hopkinson pressure bar. For shear compression, very large plastic strains of more than 5.0 were reached, in comparison with the previously reported 0.4–0.6 for cylindrical and regular SCS specimens. The large strains, which combine effects of strain rate and temperature, allow separation of these effects using the Johnson-Cook material model without performing tests at different environmental temperatures.The dynamic shear-tension tests reached plastic strainsof 2.5 at fracture, but the material's ability to sustain load in shear–tension, at a triaxiality of 0.67, starts to degrade early from plastic strain levels of 0.15. For larger plastic strains, the slope of the stress-strain curve becomes negative due to damage evolution combined with strain rate and temperature effects.Our results indicate that the material dynamic failure behaviorat high strain rates in shear-tension is markedly different from that in shear-compression, for which the rate of damage accumulation is more moderate, and hence ductility is higher.