We develop a model for the dynamics of a fully developed shear band th
at allows effective computation across several length scales, From a m
acroscopic point of view, a shear band is a discontinuity in tangentia
l velocity that supports a shear stress, Numerical simulation of the f
ull system of governing equations reveals that the internal structure
of the band consists of a quasistatic core surrounded by a thermal lay
er, We show that the shear band can be modeled as a composite structur
e whose evolution is governed by an integral equation, coupled to the
external flow through jump conditions, We establish the accuracy of th
e model equations by numerical experiments.