# Discussion Forum

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## co-efficient of thermal expansion

Hello evrybody,

Can anyone help me to know if I can input my co-efficient of thermal expansion as a function of Stress and Temperature or not. And if possible how to do that.

Thank you.

6 Replies Last Post Mar 7, 2013, 10:51 AM EST
Posted: 5 years ago
Hi

check the material library, you should have a few examples of T and pA (temperature and Absolute pressure) dependence on some materials, look how the interpolation function is defined therein, and repeat ;)

The help also describes this

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Good luck
Ivar

Posted: 5 years ago

Thanks for your reply. I saw the documentation, however I could not get the idea of how to implement in terms of stress; lets say solid.mises. Whenever I am using that term, I am getting a warning "circular variable dependency detected". Can you please refer a tutorial dealing with material properties as a function of stress?

Kanhaiya

Posted: 5 years ago
Hi

mises stress is a combination value of several stress elements, hence you get easily a circular dfinition, sometimes, you can get out of that by using an external dependent variable, I believe there is a KB case on that, if not it was on the Forum a few years ago

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Good luck
Ivar

Posted: 5 years ago
hello sir,

First we have to take co-efficient of thermal expansion (alpha) as a function of temperature and stress. After computation we will a get a new value of the stress as Von Mises stress (solid.mises). Now we want to put this new stress value(solid.mises) into alpha and compute in subsequent iterations.
How should I implement this problem in COMSOL.

Thank you
Kanhaiya

Posted: 5 years ago
Hi

if you define the expansion as function of T and the strain (instead of the stress), you remove the circular dependency, but you might not have the right equation this way ;)

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Good luck
Ivar

Posted: 5 years ago
Hi Kanhaiya,

Ivar’s suggestion is the best way to do it in my opinion. If you cannot transform the equation to use strain instead of stress you can try the following more complex approach. Define a new physics field (maybe coefficient form PDE) with one variable and set that variable equal to the Mises stress. If you then refer to that new variable in the definition of thermal expansion you should avoid the circular dependency. You have to solve that field together with the solid mechanics one, so your model will have more degrees of freedom.

Nagi Elabbasi
Veryst Engineering

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