Hi everyone, Im trying to model a rtm6 epoxy resin. I attach an image where you can see four curves for uniaxial compression test at different load velocities.

I want to model the constitutive behavior, obviously at large deformations. Id like to minimize the number of parameters because after this, Ill perform an optimization scheme in order to calibrate the constitutive parameters from another mechanical test.

Which model can you recommend me? this material shows strain softening, and hardening at large deformations. I tried with the Arruda-Boyce model, but it didnt capture the softening as I expected. After I tried with a parallel model, two networks, one with eight-chain, and in parallel other with a linear elastic spring in series with a power law dashpot with exponential evolution of yield, it was better but not enough for my expectations.... they may be too high hehe.

So, any advice with this?

Thanks in advance

Lucas