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Non-linear material Simulation
Posted 19 août 2014, 14:28 UTC−4 Materials, Parameters, Variables, & Functions, Structural Mechanics Version 4.4 3 Replies
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I know that, in COMSOL, I can define a linear material by entering the values of modulus of elasticity, Poisson's ratio and the density of the material. Also, I can define a hyperelastic material by choosing the suitable model like Mooney-Rivlin or other models.
However, if I have a special non-linear material and I have the result of uniaxial tensile test(stress- strain table), could I use this table to define this material in COMSOL?
Do I need another test for this material such as bi-axial test, shear stress or volume compression test to define this material?
I want to simulate the stresses within a gasket by using COMSOL so, I bought some samples and I going to test this material by using the universal testing machine to get the stress-strain data.
I hope to get the way how to use these data within COMSOL to simulate this gasket material under compression.
Thank you for your support
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As long as the properties in the transverse direction are not important, a uniaxial test is sufficient. For a gasket that would probably be the case.
The next question is whether the loading on your structure in the real load case is a pure onloading, or if it is cyclic. In the first case, a monotonic test and a non-linear elastic material is sufficient. If not, then you need something like plasticity.
Assuming that you can do with only elasticity, a simple approach is to use the linear elastic material, but make the modulus of elasticity strain dependent. If you measure you stress-strain-curve as
and combine it with the law from linear elasticity
the you should give Young's modulus as
In COMSOL you could write something like
f(solid.eZ)/solid.eZ
where f is a function containing your measured data in the input field for E.
This will however fail when starting the algorithm, since the strain is zero, and there will be a zerodivde. You will have to use a slightly more sophisticated expression, like
if(abs(solid.eZ)<1e-6,f(1E-6)/1E-6,f(solid.eZ)/solid.eZ)
Regards,
Henrik
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Well, I would be grateful if I can get your advice about the following:
I want to study the effect of the gasket's material on the contact pressure between the components of a Proton Exchange Membrane Fuel Cell Stack(please see the attached file). So my question is :
Is it possible, by using COMSOL , to simulate this case in 3D by applying a clamping force (using bolts) ?
Thank you
Yours sincerely
Aimen
Attachments:
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Yes, you can model that. Use the Contact and Bolt Pre-Tension features.
Take a look at the example 'Prestressed Bolts in a Tube Connection' in the Model Library to get started.
Two side remarks to your original question:
1. You can use an orthotropic material if you want to have the strain dependence of the modulus of elasticity only in the compression direction.
2. In general, a material like the one I sketched will not be theoretically sound from a thermodynamics point of view. It may possible to extract energy by loading it in certain stress-strain cycles. Nevertheless, it is useful as an engineering approximation for cases like yours.
Regards,
Henrik