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Poissons ratio and volume change

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Posts: 3
Topic starter
(@vinasebho)
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Joined: 13 years ago

Hi everyone,

I have one question about Poissons ratio and volume change.

Im building a FE model of cells and surrounding ECM under 20% uniaxial compression. Im using 0.49 as the Poissons ratio of the cells and 0.4 for the ECM. However, as a result, Im getting a lot (more than 20%) volume change for the cell. When I raised the Poissons ratio of the cells from 0.49 to 0.499999, I got almost no volume change, which was expected. Since 0.49 is already nearly incompressible, why there is such a big difference by using 0.49 and 0.49999. I was expecting almost no volume change with either one. It seems like that during the analysis process, ABAQUS is kind of loosing the constraint from high Poissons ratio. But what and how did this happen?

Im using hybrid element and reduced integration for the cells with ABAQUS, NLGEOM on.

Thanks a lot!

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Posts: 3998
(@jorgen)
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Joined: 5 years ago

I am not quite sure I understand your question, but to me there is quite a large difference between 0.49 and 0.49999.
Can you develop a simpler model that you can also solve and verify by hand?

-Jorgen

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3 Replies
Posts: 3
Topic starter
(@vinasebho)
New Member
Joined: 13 years ago

Thank you for your reply Dr. Bergstrom!

My problem is that Im not getting the reasonable cellular volume change according to the Poissons ratio I assigned to the cell. For Poissons ratio of 0.49, I got quite constant about 20% cellular volume reduced with different element types, such as c3d4h, c3d10h, c3d10mh, c3d10i.

My simplified model includes a spherical soft inclusion with about 200 times softer (in terms of E) material than surrounding material. Linear elastic materials were used for both components. SYMM BCs were applied to this quarter model, with 20% compressive strain applied on the top surface.

My question is, does this big mismatch of E (200 times difference), which leads to mismatch of K, will influence the constraint from the Poissons ratio? Is there anything that I can do to get a reasonable volume change?

Thanks a lot for your help in advance!

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

I have a hard time fully understanding your problem. In a fully confined geometry, which sounds like your problem, the Poissons ratio can play a large role.
Best of luck!

-Jorgen

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