Discussion Forum

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