Model a viscoelastic-viscoplastic material

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October 25, 2013 10:59pm UTC

Model a viscoelastic-viscoplastic material

Dear All,

The material models such as plasticity, creep, and viscoplasticity under Linear Elastic Materials node cannot be assigned to a material which has been used as a Linear Viscoelastic Material. I wonder how a viscoelastic-viscoplastic material is modeled in Comsol? Any suggestions or discussions are appreciated.

Thank you,
Steve

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Henrik Sönnerlind

Henrik Sönnerlind
COMSOL Employee
Sweden
Moderator

October 28, 2013 9:22am UTC in response to

Re: Model a viscoelastic-viscoplastic material

Hi Steve,

In version 4.4 (soon to be released) this limitation is removed. The viscoelastic material has been moved to be a subnode under Linear Elastic, and has also improved with a number of new options.

In the current version it is rather difficult to do what you want, but one way could be to use two separate Solid Mechanics interfaces (but with the same degrees of freedom). In one of them a viscoelastic material is used, and in the other one a viscoplastic material is used. The interfaces could then communicate the viscoelastic stress and viscoplastic strain through the Initial stress/strain features.

Regards,
Henrik

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Steve Chang

Steve Chang

October 28, 2013 3:37pm UTC in response to Henrik Sönnerlind

Re: Model a viscoelastic-viscoplastic material

Dear Henrik,

Thank you so much for your helpful replies. It would be a really good news if the viscoelasticity and viscoplasticity can be modeled simultaneously in the following version of Comsol. I will also try your suggestions on using two separate Solid Mechanics interfaces for now.

I had another questions and would like your and anyone's opinions:
The Anand model is the only option for viscoplasticity in the current version of Comsol. If I want to build a new viscoplastic (not plastic) model using a different yield surface, plastic potential, and flow rule, how can I define them in Comsol? My thinking to this problem is to define them as a "Potential" model under "Creep" node. Do you have any suggestions on this?

Thank you again,
Steve



Hi Steve,

In version 4.4 (soon to be released) this limitation is removed. The viscoelastic material has been moved to be a subnode under Linear Elastic, and has also improved with a number of new options.

In the current version it is rather difficult to do what you want, but one way could be to use two separate Solid Mechanics interfaces (but with the same degrees of freedom). In one of them a viscoelastic material is used, and in the other one a viscoplastic material is used. The interfaces could then communicate the viscoelastic stress and viscoplastic strain through the Initial stress/strain features.

Regards,
Henrik

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Henrik Sönnerlind

Henrik Sönnerlind
COMSOL Employee
Sweden
Moderator

October 29, 2013 7:34am UTC in response to Steve Chang

Re: Model a viscoelastic-viscoplastic material



I had another questions and would like your and anyone's opinions:
The Anand model is the only option for viscoplasticity in the current version of Comsol. If I want to build a new viscoplastic (not plastic) model using a different yield surface, plastic potential, and flow rule, how can I define them in Comsol? My thinking to this problem is to define them as a "Potential" model under "Creep" node. Do you have any suggestions on this?



Hi Steve,

The term 'viscoplasticity' is not unique, so there could be different approaches depending on the actual physics described by your constitutive equations. Your approach is one which seems good. For other cases, using Plasticity, but with strain rate dependent material data could also be a possibility.

By the way: If you will try the 'two interface approach', note that only one of them should actually produce a stiffness contribution. So you need to go into Equation view and remove the weak expression (stress:test(strain)) for the viscoelastic material. If not, there will be double stiffness contributions.

Regards,
Henrik

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