Numerical study of shear deformation in Ti-6Al-4V at medium and high strain rates, critical impact velocity in shear

A fast shear deformation with the effect of adiabatic coupling is studied in this paper for Ti-6Al-4V alloy by application of the finite element technique. The numerical study of impact shearing of a layer with a small imperfection in geometry has been completed for a wide range of impact velocities by FE Code ABAQUS and the results have been compared with experiments. Advanced constitutive relations were used which take into account strain hardening, strain rate and temperature sensitivities. The experimental results were obtained earlier for Ti-6Al-4V alloy by direct impact on modified double shear specimen. The numerical study was focussed on the effect of the imposed velocity on the spatial deformation in the deformed layer. Seventeen imposed velocities were assumed in FE calculations, from quasi-static to impact up to 180 m/s. In general, two modes of shear deformation of the layer were found: in the first mode all plastic deformation is concentrated in the middle of the layer. that is in the smallest cross-section, and in the second case the localization occurs near the surface where the shear velocity is imposed. This is the phenomenon of the critical impact velocity (CIV) in shear. Deformation trapping near the impact surface. due to thermoplastic instability and localization caused by superposition of plastic waves, is the main physical reason for the CIV in shear. It has been shown that impact velocities higher than the CIV leads to a substantial reduction in the total energy of strain localization, a very important effect in fragmentation. (C) 2002 Elsevier Science Ltd. All rights reserved.