Comparison between high and low Strain-Rate deformation of tantalum

To understand the constitutive behavior of tantalum, compression tests are performed over the range of strain rates from 0.0001/s to 3000/s, and at temperatures from 296 to 1000 K. The flow stress is seen to be representable as the sum of a thermal, an athermal, and a viscous drag component. At high strain rates (3000/s), the thermal component is observed to be expressible in terms of the temperature and the strain rate, whereas the athermal component is independent of these variables. At lower strain rates, however, such a separation of the effects of the strain, strain rate, and temperature on the flow stress is not easily achieved. At high enough temperatures, i.e., temperatures above which the thermal component is essentially zero, viscous drag appears to have a significant effect on the flow stress.