  Starting from the assumption that all possible orientations of grains are
equally probable, we prove that the geometric factor of thermodynamic
dislocation theory for polycrystals subjected to axially symmetric tension or
compression must be equal to 2. We then use large-scale least-square analysis
to identify the physics based parameters of this theory and show that the
simulated stress-strain curves for OFHC copper, ARMCO iron and 4340 steel agree
well with the experiments of Johnson and Cook.
