A constitutive relation and failure criterion for Ti6A14V alloy at impact rates of strain

Shear stress-strain curves have been obtained for thin-walled tubular specimens of Ti6Al4V alloy at strain rates from similar to 7 x 10(-4)/s to similar to 1000/s. A specially developed infrared radiometer has been used to measure the rise in specimen surface temperature during the high strain rate tests where the deformation process is essentially adiabatic. The data obtained were used to obtain material constants for a Zerilli-Armstrong type constitutive relation giving the 'best fit' with the observed mechanical response. This relation was incorporated in the ABAQUS/explicit FE code and shown to predict the experimentally measured flow stress in the impact tests with reasonable accuracy. A failure criterion, based on a critical value of effective plastic strain, is also incorporated, the critical condition being chosen to give agreement between the predicted and the measured overall failure strains. The validity of the constitutive relation and associated failure criterion is then assessed in terms of their ability to predict the observed mechanical response in tensile impact tests on specimens of both cylindrical and rectangular cross-section where the early onset of localised plastic Bow and significant temperature rises in this region provide a more rigorous test of the proposed model. High-speed photography was used to monitor the changing specimen cross-section and the infrared radiometer was used to determine the specimen surface temperature in the region of localised deformation. Reasonable agreement was obtained between the experimental results and the numerical predictions using the ABAQUS/explicit FE code. (C) 1999 Elsevier Science Ltd. All rights reserved.