Discussion Forum

Hi everyone,

I’m currently working with COMSOL 4.2a to simulate the strain and stress in multiple thin films.
The model contains three layers. Firstly, layer 2 is deposited on layer 1 under 220 deg C. Then let layer 1 and 2 cool to room temperature (20 deg C). Secondly, layer 3 and 4 are deposited on layer 2 at 20 deg C. Please see the attached file.

Please give me some suggestions on how to solve the following problems:
1. How to set the boundary conditions
Refer to the reference “thermal stresses in a layered plate” in the Model Gallery, there is no constraint on the interface between two contact layers. However, in my case, Comsol calculates the thermal strain of each layer separately, but does not show the gradient of thermal strain between two contact layers. Is it necessary to set additional boundary conditions?
2. Initial stress and strain
The reference mentioned to set InitStrain as a parameter under Global Definitions, and then insert InitStrain to solid.eX under the node of initial stess and strain. How about the other components, such as solid.eY and solid.eZ. Do I need to set all these equal to InitStrain? How about the case of initial stress?
3. Infinite boundary
The boundary of the three layers is supposed to be infinite and there is no boundary effect on the stress and strain states in the films. In this case, how to apply the infinite boundary condition to the edges. Could you please show me how to use the “infinite element domain” to set left/right/bottom edges as infinite? There is no such options such as Scaling direction, Geometric width, or Coordinate at interface.
I have tried to fix the bottom left corner and constrain the bottom right corner for the model, but it seems like it will influence the stress and strain distribution.

Please let me know your suggestions. Your early reply will be highly appreciated.

Sincerely,
Elva