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Modeling Negative Stiffness Structure in series with resin (large strains)
Posted 02.03.2016, 18:06 GMT-5 Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 4.4 3 Replies
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I'm modeling a metal NSS with a block of resin on top of it in 2D. I've set two constraints: fixed constraint on the bottom of the structure and prescribed displacement on the top of the resin. In other words, I want to compress the ensemble enough for it to show the negative stiffness behavior of the structure.
When I run the model using high values of Young's Modulus of the resin (E>400 kPa), it works fine. Nevertheless, if I use values of E smaller than 400kPa, I'm only able to run the model with very small displacements, which prevents me from observing the negative stiffness behavior. With larger displacements I get the following error: Failed to find a solution for all parameters, even when using the minimum parameter step...
I believe that the problem relies on the fact that the resin is subject to too large strains, since the E_resin<<E_structure (the structure works perfectly fine by itself).
Is there a way to make it work for small values of E (with large strains)? Do I have to get the nonlinear structural materials module?
Thank you so much for your help.
PS: I tried to submit the file but I got an error related to the file size .
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Linear elasticity and large compressive strains can be problematic. This is discussed in
www.comsol.se/blogs/modeling-linear-elastic-materials-how-difficult-can-it-be
If you do 'Clear Solutions' and 'Clear Meshes' your file size will decrease significantly, and it may be possible to upload it.
Regards,
Henrik
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I have read the blog discussion but I'm still not sure what to do to make the model run. They suggest to change to a suitable hyperelastic material model... Does this require the Nonlinear Structural Materials Module? or is there anything else I can do?
Please find attached a copy of my model.
Thanks again!
Attachments:
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Yes, hyperelastic materials require the Nonlinear Structural Materials Module.
www.comsol.se/nonlinear-structural-materials-module
Since your material model probably is far of from reality anyway, you can consider playing around with E and nu a bit and see how far you can get. Plot the smallest principal strain (solid.ep3) at non-convergence to see how bad it is.
Regards,
Henrik