High strain-rate response of commercially pure vanadium

To understand the plastic ̄ow behavior of commercially pure vanadium under high strain rates, uniaxial compression tests of cylindrical samples are performed using UCSD's enhanced Hopkinson technique. True strains exceeding 50% are achieved in these tests, over a range of temperature from 77 to 800 K at the strain rates of 2500 and 8000 sÿ1. The microstructure of the deformed and undeformed samples is observed by an optical microscope. The initial microstructure (the initial dislocation density, the grain size and its distribution) is found to have a strong e€ect on the yield stress and the initial stages of the ̄ow stress. This e€ect becomes more signi®cant with decreasing temperature. Deformation twins are observed. Their density is seen to increase with decreasing temperature. Adiabatic shearbands occur in vanadium at low temperatures. Finally, an experimentally based micromechanical model is developed for the dynamic response of this material. The model predictions are compared with the results of other high strain-rate tests which have not been used in the evaluation of the model parameters, and good agreement between the theoretical predictions and experimental results is obtained. In addition, the results of a series of low strain-rate tests are presented and brie ̄y discussed. Ó 2000 Elsevier Science Ltd. All rights reserved.