Elastomer modeling comparison

[Jorgen]

This paper outlines the current state of the art in finite element modeling of elastomers, and exemplifies the predictive capabilities of modern constitutive theories for filled elastomers.

[burgeand]

Dear Jorgen,

I have read your summary of constitutive models of Elastomers.

In the section where you discuss the BB model you state that the other models "are all inherently incapable of predicting rate-dependence, hysteresis, and the response during cyclic loading". I am especially refering to the Qi-Boyce model. Qi-Boyce have developed a constitutive model for PU (2005) that builds upon the model you looked at in your comparision. Is it correct that this newer model overcomes some of the short comings you mentioned in your document?

Kind regards,
Andreas

[Jorgen]

I am familiar with the Qi-Boyce model for PU, and yes, that model is certainly capable of capturing both rate-dependence and hysteresis. Good point.

-Jorgen

[burgeand]

Hi Jorgen,

Another question concerning the BB (and the Qi-Boyce) model:

In my project I'm also interested in the long-term creep/relaxation behaviour of PU. Both the BB and the QB model include compression tests with short term strain holding periods (relaxation) to indentify the equilibrium stress-strain response. Since the material is not completely relaxed after these short periods I was wondering if I could combine these constitutive models with some sort of "pure" viscoelastic model (coefficients derived from either long-term creep/relaxation experiments or from DMA). Or do you think it is possible to lengthen the short holding periods?

Thanks very much for your help.
Andreas

[Jorgen]

My recommendation is to lengthen the holding periods. You can make them as long as you want. The BB and the QB models should work well also for long-term creep/relaxation behavior.

- Jorgen

[burgeand]

Thanks for the help.

Andreas

[burgeand]

Hi Jorgen,

I have another question concerning the BB model.

Did you use constant true strain rates in the mechanical experiments? The reason I'm asking is because the Qi-Boyce model uses true stress/strain together with constant true strain rates. In the BB model you also use true stress/stress so I figured you probably also used true strain rates.

I've been trying to figure out if constant engineering strain rates could instead be used. I haven't come to a conclusion yet if it matters.

Thanks
Andreas

[Jorgen]

Yes, I also used constant true strain rate. There is no reason, however, why you could not use constant engineering strain rate. I recommend that you use whatever is easier for you to use.

-Jorgen