  We show that the thermodynamic dislocation theory (TDT) predicts a scaling
relation between stresses, strain rates, and temperatures for steady-state
deformations of crystalline solids, and that this relation is accurately obeyed
by a wide range of experimental data for both aluminum and copper. Unlike
conventional phenomenological dislocation theories, the TDT is based on the
second law of thermodynamics. Its success implies that descriptions of solid
deformation that are not based on the statistical mechanics of nonequilibrium
processes cannot be relied upon to be predictive. Thus there is an urgent need
-- and a new opportunity -- to revitalize this central part of materials
physics.
