equilibrium curve in hysteresis loop

[nut]

hello Dr.Berstrom
I have the question about hysteresis model in elastomer.Now i have got the result in my experiment in conpression rubber block load-unloading at different strain rate.I want to predict hysteresis loop by using abaqus compare with my experiment.I'm trying to detemine the parameter c1,c2,m,sigmaB but the most important thing that I must estimate is equilibrium curve because if the equilibrium curve not appropriate with the result,other parameters will be different. I try it many times by using polynomial theory estimated between load-unloading curve but i'm not sure it is correct.That is my problem.I have the result in load and unloading in NR70 at many strain rate.How i can predict the equilibrium curve?

Thank a lot for your answer,
Nut

[Jorgen]

The equilibrium curve corresponds to the behavior of the material at "very slow" deformation rates. As a first approximation you can take the equilibrium curve to be in the middle between the loading and the unloading curves. To be more precise, it turns out that the equilibrium curve is typically slighly closer to the unloading curve than the loading curve.

Another way to estimate the location of the equilibrum response is to use stress relaxation tests as discussed in this paper (http://www.polymerfem.com/modules.php?name=Downloads&d_op=getit&lid=2).

- Jorgen