The strain rate and temperature dependence of the dynamic impact response of tungsten composite

Liquid sintered tungsten (W) heavy alloy with a 92.5W-5.25Ni-2.25Fe composition was examined using a compression split-Hopkinson bar to realize the effects of strain rate and temperature on dynamic impact deformation behaviour. Both stress and strain were measured for specimens tested at temperatures ranging from 25 to 1100 degrees C and strain rates ranging from 8 x 10(2) to 4x10(3) s(-1). The relationship between flow stress, strain rate and temperature was determined and the results have been successfully modeled by a proposed constitutive equation incorporating the effect of strain, strain rate and temperature. Our results show that flow stress increases with increasing strain rate. Alternatively, high temperature reduces flow stress significantly and improves the degree of thermal softening. During impact, initial cracking occurs preferentially either at tungsten-tungsten grain boundaries or at the tungsten-matrix interface, and failure is dominated principally by a mixture fracture model. Metallographic examinations show a dramatic increase in microcrack density and deformation of tungsten grains as strain rate and temperature are increased. Additionally, changes in microhardness are also found to correlate with changes in strain rate and temperature. (C) 1998 Elsevier Science S.A. All rights reserved.