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How to specify a strain-energy function for a hyperelastic material?

Posted 16 juil. 2010, 16:54 UTC−4 4 Replies

Christine Buffinton
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COMSOL v4 has a choice for a user-defined strain-energy-density function for a hyperelastic material.
However, we can find no documentation about how to enter this function and nothing obvious seems to work.
There is a box labeled "Ws", we have tried the obvious Matlab-syntax forms for an exponential in the input box:

a * ( exp( b * ( I1 - 3 ) ) - 1 )

where a and b are both numbers and I1 is the first strain invariant (from the user guide, it looks like we should be able to use this symbol I1, but again there is no example).

Has anyone been able to successfully create a hyperelastic material with a user-defined strain-energy-density function?

Thank you,
Christine Buffinton
Dept. Mechanical Engineering
Bucknell University

4 Replies Last Post 12 avr. 2011, 10:14 UTC−4
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Hello Christine Buffinton

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Mazyar Amin
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Posted: 1 decade ago 23 sept. 2010, 11:07 UTC−4

COMSOL v4 has a choice for a user-defined strain-energy-density function for a hyperelastic material.
However, we can find no documentation about how to enter this function and nothing obvious seems to work.
There is a box labeled "Ws", we have tried the obvious Matlab-syntax forms for an exponential in the input box:

a * ( exp( b * ( I1 - 3 ) ) - 1 )

where a and b are both numbers and I1 is the first strain invariant (from the user guide, it looks like we should be able to use this symbol I1, but again there is no example).

Has anyone been able to successfully create a hyperelastic material with a user-defined strain-energy-density function?

Thank you,
Christine Buffinton
Dept. Mechanical Engineering
Bucknell University



Christine,

Have you added the extension of your model to the first invariant like "I1_smaxi" ?
Have you also taken a look at the tutorial example than uses Neo-Hokean, and get some ideas from their equation in Physics/Equation System/Subdomain Setting/Variables ?

We could manage feed our W but could not get very reasonable results comparing to our experimental and modeling results yet.

I hope this helps.
[QUOTE] COMSOL v4 has a choice for a user-defined strain-energy-density function for a hyperelastic material. However, we can find no documentation about how to enter this function and nothing obvious seems to work. There is a box labeled "Ws", we have tried the obvious Matlab-syntax forms for an exponential in the input box: a * ( exp( b * ( I1 - 3 ) ) - 1 ) where a and b are both numbers and I1 is the first strain invariant (from the user guide, it looks like we should be able to use this symbol I1, but again there is no example). Has anyone been able to successfully create a hyperelastic material with a user-defined strain-energy-density function? Thank you, Christine Buffinton Dept. Mechanical Engineering Bucknell University [/QUOTE] Christine, Have you added the extension of your model to the first invariant like "I1_smaxi" ? Have you also taken a look at the tutorial example than uses Neo-Hokean, and get some ideas from their equation in Physics/Equation System/Subdomain Setting/Variables ? We could manage feed our W but could not get very reasonable results comparing to our experimental and modeling results yet. I hope this helps.
John Peterson
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Posted: 1 decade ago 23 sept. 2010, 18:42 UTC−4
Hi Cristine,
I don't have Comsol on this computer, but as far as I remember, the invariants are called (let's suppose you have only one solid mechanics application mode)
solid.I1e, or solid.I1, depending on whether you are using the invariant of Green-Lagrange strain E, or right Cauchy-Green deformation tensor C. Check the equation view to be sure.

By the way, which hyperelastic material are you trying to implement?
cheers
john
Hi Cristine, I don't have Comsol on this computer, but as far as I remember, the invariants are called (let's suppose you have only one solid mechanics application mode) solid.I1e, or solid.I1, depending on whether you are using the invariant of Green-Lagrange strain E, or right Cauchy-Green deformation tensor C. Check the equation view to be sure. By the way, which hyperelastic material are you trying to implement? cheers john
Jean-Christophe Lavocat
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Posted: 1 decade ago 12 avr. 2011, 06:19 UTC−4
Hi Manuel,

Which model is using the neo-hookean material? I could not find it..
Hi Manuel, Which model is using the neo-hookean material? I could not find it..
Mazyar Amin
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Posted: 1 decade ago 12 avr. 2011, 10:14 UTC−4
Hi Jean-Christophe,

It is under Structural Mechanics, and in the Subdomain Setting, Material tab, Material Model.

Manuel.



Hi Manuel,

Which model is using the neo-hookean material? I could not find it..


Hi Jean-Christophe, It is under Structural Mechanics, and in the Subdomain Setting, Material tab, Material Model. Manuel. [QUOTE] Hi Manuel, Which model is using the neo-hookean material? I could not find it.. [/QUOTE]

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