Measuring damage variables from load-unload test (damage mechanics)

Hi All,

I want to use ductile damage model in ABAQUS to model the damage of thermoplastic polymers, in which I need to input the damage evolution law (\dot{d}).

My question is on the way we have to measure the variable d.

Suppose I have 10 cycles of load-unload test. For slope of the first load will be initial Young's modulus at undamaged state E_0. now for the next cycle, which part of the curve we need to measure their slope to get the damage variable (d = 1 - E/E_0).

Is is the slope of the loading part of the cycle, or unloading part of each cycle, or slop of the line from the loest point to the peak point of the cycle? Since different way of measuring the slope will give different damage evolution law, so I think it is better to disccuss with people which has more experience on damage mechanics.

Best,

Ditho