This paper is concerned with crystals undergoing large plastic deformations
. The free energy per unit volume of the reference crystal is supposed to d
epend on the elastic distortion as well as on constant tensors characterizi
ng the crystal symmetry. The dissipative driving force is shown to be equal
to the Eshelby stress tensor relative to the reference crystal. For single
crystals obeying Taylor's equation the driving force reduces to the Eshelb
y resolved shear stress, which is power-conjungate to the slip rate. The Sc
hmid law formulated with respect to the latter is used to determine the cri
tical hardening rate at the onset of the shear band formation. (C) 1998 Els
evier Science Ltd. All rights reserved.