HIGH-STRAIN, HIGH-STRAIN-RATE BEHAVIOR OF TANTALUM

Tantalum plate produced by a forging-rolling sequence was subjected to high plastic shear strains (gamma = 1 --> 5.5) at high strain rates (similar to 4 X 10(4) s(-1)) in two experimental configurations: (a) a special hat-shaped geometry and (b) thin disks deformed in a split Hopkinson bar. In parallel experiments, the constitutive behavior of the same material was established through quasi-static and dynamic compression tests at ambient and elevated temperatures. The microstructure generated at high strain rates and retained by rapid cooling from a narrow (200-mu m) deformation band progresses from dislocated, to elongated cells, to banded structures, and finally, to subgrains as the shear strain increases from 0 to 5.5. The temperature rise predictions from the constitutive description of the material indicate that the temperature reaches values of 800 K, and it is proposed that thermal energy is sufficient to produce a significant reorganization of the deformation substructure, leading to a recovered structure.