# Hyperelastic modelling

Member

Hello guys,

I'm trying to help a friend with your master's degree. He needs to compare a experimental data with a FEA data. We have a Uniaxial Tension data of a hyperelastic material. Usually I work with cfd, It's my first simulation with this materials.

So, I searched some videos, forums, papers, but I feel losting yet.

I input the data on ansys: strain (this is simple strain (Δl/lo) or I have to use Stretch ratio (λ) ?) and stress (F/A)

and I choose the method (Yeoh 1st order), solve the curve fit and copy the calculated values:

And I have to compare the exp data with 12 methods [Mooney-Rivlin (3, 5 e 9 parameters); Ogden (1a, 2a e 3a order; Yeoh (1a, 2a e 3a order); Polinomial (1a, 2a e 3a order).]

Then I put this material on my project (Static structural).

I set the mesh:

Then, my boundary conditions: (dispacement = 195mm (like the max displacement on experimental test))

Set my Analysis settings: (most are set as default)

When I run my simulations I have the follow results:

But I don't know if is a correct, because when I compare to experimental data is so different:

I have no idea where the error is, if it exists. Or if it is problems in my engineering interpretations, I am still studying this type of material and its behavior and applications in FEA. Can someone help me? Tips, useful links, things like that?

Sorry for the long post and thanks for any help.

André Moura

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• Member

Hello,

To answer your first question: In Engineering Data, engineering strain is used i.e. the simple strain formula you mentioned above.

But in the final results, you get the true stress and true strain. This might be the reason your FEA results differ from the experimental results. One way to compare the FEA and experimental results, would be to use Force reaction from FEA and divide it by the original cross-sectional area. This will give the nominal stress which is probably what the experiment measures.

Hope this helps,

Sai

• Member

Thanks so much, it was very helpful.

I've this domain

When I put tha face b left as "fixed support" and b right as "displacement" I have the results (force reaction) very closed to my experimental data, but when I put the face A left as "fixed support" and A right as "displacement", my results are about half. I'm very confused on this point.