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 Hop kinson bar. In parallel experiments, the constitutive behavior of the same material was established through quasi-static and dynamic compres sion tests at ambient and elevated temperatures. The microstructure ge nerated at high strain rates and retained by rapid cooling from a narr ow (200-mu m) deformation band progresses from dislocated, to elongate d 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 tempera ture reaches values of 800 K, and it is proposed that thermal energy i s sufficient to produce a significant reorganization of the deformatio n substructure, leading to a recovered structure.