Modelling hyperelasticity

[Cheesella]

Hello everyone,

I am trying to model the behaviour of hyperelastic material under cyclic loading (compression behaviour, not shear). The initial slope of the load displacement graph is small, but the slope keeps increasing exponentially with increase in displacement (and does not decrease or yield). The final slope of the loading branch (k4) is greater than the initial slope of the loading branch (k1). For unloading, the initial slope of the unloading branch must be greater than k4 (and hence k1).

I tried to use the Multilinear material, but it's not working for my case. I realized that it's because in the Multilinear material model, the initial stiffness k1 is greater than the final stiffness k4, and the unloading branch follows the slope of the loading branch in the order k1, k2, k3, k4. I have looked at material models available for elastomeric bearing and if I have understood it correctly, it seemed to me that those are more suited for modelling the behaviour in shear. The initial stiffness is also greater than the final stiffness for the loading branch in those models.

Any suggestions/ideas regarding how I can model this appropriately would be greatly appreciated!