Load
– stroke data analysis
The load – stroke curves were
converted using a computer program into true stress – true plastic strain
curves, first by subtracting the elastic portion of both the material and the
machine from the stroke values at each of the loads, and then by using the
standard equations:
s
=
P/Ao (1 – e)
e = - ln (ho/h)
where
s is the true stress, P is the Load, Ao is the
original area of cross section of the specimen, e is the engineering strain
given by (ho-h)/h, e
is the true plastic strain, ho is the original height of the specimen, and h
is the instantaneous height. The
program uses about 100 data point to
plot a smooth curve covering a true strain of about 0.6.
Map
program
The
flow stress data obtained at constant temperature, strain rate and strain are
corrected for the adiabatic temperature rise by applying linear interpolation
between log(flowstress) and (1/T) values.
Cubic spline interpolation is carried out to compute the flow stress
values at finer temperature and strain rate intervals, using the experimental
data points as knots. The value
of strain rate sensitivity (m) in each of these subintervals is calculated and
the efficiency of power dissipation and instability parameter values are
computed and plotted in the temperature-strain rate plane to obtain power
dissipation and instability maps r espectively.
For further details, contact R.Ravi at ravi@processingmaps.com