# Elastomer Constitutive Model Accuracy in Compression?

I have some data from three standard tests perfomed on an elastomer (uniaxial tension, equibiaxial tension and planar tension) for use to develop a constitutive model. I understand that the models are developed based upon equivalent principal stretches/deformation modes, e.g., uniaxial tension = equibiaxial compression. However, what I am failing to grasp is how do you know that your constitutive model developed is accurate in the compression region? To be clear, the tests I had performed provide positive stress vs. positive strain results and I can generate a number of constitutive models (ogden, mooney-rivlin, etc.) that all match the experimental data well in the tensile region, but have completely different responses in the compression region where I have no data. Thanks in advance.

I dont know what material you are studying, but if you capture the tensile response of an elastomer then you typically also relatively accurately capture the compressive response.

-Jorgen

Thanks for the response, however I still do not understand how you know youve captured the compressive response. The material is Viton. Attached is the biaxial response which includes the test data (from the biaxial tension test) and the response predicted by two fitted models using Abaqus/CAE -- a 2nd-order Ogden and a 1st order reduced polynomial (Neo-Hookean). If you were able to zoom into the tensile region you would see the models fit the data fairly well. However, from the figure it is clear the compression region gives you completely different results for the models. So, to your point, I believe the models are able to accurately capture the tension response, but diverge significantly in the compressive region -- obviously both cannot be correct. Therefore, how do you know which one is more correct? Thank you.

[QUOTE=Jorgen,11713]I dont know what material you are studying, but if you capture the tensile response of an elastomer then you typically also relatively accurately capture the compressive response.

-Jorgen

Ok. I get your question. My comment about matching the compression response was based on using certain material models. Other material models, like the Ogden model, are notorious for being difficult to capture both tension and compression behaviors from only, say, tension data. In other words, dont use the Ogden model in that case, OR run more experiments...

-Jorgen

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