1. 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.


  1. 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