The m value has been customarily determined from
the slope of a log–log plot of the flow stresses at a
constant strain versus the nominal strain rates. In a
strict sense, this is not correct at all since, even though
the strain is fixed constant, the flow stresses at such a
strain are not those obtained at the nominal strain rates
that were set prior to deformation; the actual strain rate
decreases with increasing true plastic strain when tensile
test is carried out at a constant cross-head speed.
Accordingly a correct deduction of the m value must be
made from the slope of a log–log plot of the flow