Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Thermal expansion boundary condition : free deformation but keep in flat

Please login with a confirmed email address before reporting spam

Hi friends,

I am building a model which is a cubic unit cell of a composite material. At the center of the unit, there is a SnO2 fiber, and the other materials of the unit is Ag. It is built to represent an infinite large composite of Ag matrix and SnO2 fiber precipitates.

Now I am studying the thermal expansion behaviors of this material. Specifically, the thermal shock behaviors. I add the 'thermal stress' multiphysics which contains the 'solid mechanics' and 'thermal transfer in solids', and model the heating process and cooling process.

As the tempearture changes, the solid would expand differently due two different coefficients of thermal expansion (CTE). Because of the periodic and symmetry of the unit, each surface of the cubic should expand or contract as tempearture changes but all remains flat. However, I do not find a surface condition in COMSOL 'solid mechanics' to achieve it.

I believe that the physics of this condition should be 'the integral of the normal stress over each surface is zero' in which the SnO2 part suffers tensile stress(with lower CTE and expand less) and Ag part suffers compression (higher CTE and expand more).

However, in COMSOL solid mechnics, I did not find such condition. The boundary are fixed by either fixed displacement(such as roller, which supress the expansion) or stress on it. Even the 'Rigid Connector' supress the deformation.

Do you have any suggestion or idea on it?

Thanks

David


1 Reply Last Post 26 août 2019, 05:23 UTC−4
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 5 years ago 26 août 2019, 05:23 UTC−4
Updated: 5 years ago 26 août 2019, 05:23 UTC−4

Hi,

From version 5.4, there are two features which simplifies this type of modeling: Cell Periodicity (an RVE method) does exactly this, and there is also a reaction free symmetry condition.

https://www.comsol.com/release/5.4/structural-mechanics-module

Since it seems you are using an older version, you can instead use the method suggested in this tutorial model:

https://www.comsol.com/model/thermo-mechanical-analysis-of-a-surface-mounted-resistor-481

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi, From version 5.4, there are two features which simplifies this type of modeling: Cell Periodicity (an RVE method) does exactly this, and there is also a reaction free symmetry condition. Since it seems you are using an older version, you can instead use the method suggested in this tutorial model: Regards, Henrik

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.