High strain-rate shear-strain localization in f.c.c. crystalline materials: a perturbation analysis

A new perturbation formulation has been developed that is based on a rate-d ependent crystalline plasticity constitutive formulation to investigate pla nar high strain-rate instabilities and shear-strain localization in face-ce ntered cubic (f.c.c.) crystalline materials. This new formulation can accou nt for strain-rate sensitivity Values that range from rate-independent to h ighly rate-dependent values. Hence, accurate and detailed predictions of ma terial instabilities and shear-strain localization can be obtained for high strain-rate deformations of crystalline materials that are rate-sensitive, such as f.c.c. materials. Critical instability parameters are obtained for deformation modes that account for the effects of strain-rate history, ine rtia, strain-hardening, wave number, and thermal and geometrical softening for applied strain-rates that range from 100 to 5000 s(-1). Post-instabilit y behavior and localization modes are monitored by tracking the rate of gro wth of stability parameters beyond the initial instability point. Results f rom these perturbation analyses are in good agreement with rate-independent limiting cases and high strain-rate experimental observations. The present study underscores the importance of characterizing material instabilities and shear-strain localization in terms of the competing softening and harde ning mechanisms of the lattice structure. (C) 2000 Elsevier Science Ltd. Al l rights reserved.