MICRESS Forum

Dear Bernd,

I have a question regarding the boundary conditions for elastic stress calculation in MICRESS.

In the input settings, I noticed that it is possible to define a mixed boundary condition, where a normal strain is prescribed in one direction (e.g., z-direction), while an additional stress (pressure) is applied in another direction (e.g., x-direction).

I would like to understand:

What is the physical meaning of this mixed boundary condition?
Why is it valid to impose strain in one direction while prescribing stress in another?
In what situations is this type of boundary condition typically used?

From a mechanics point of view, I am trying to better understand how this combination corresponds to real physical loading conditions.

Any explanation or references would be greatly appreciated.

Thank you very much for your help.

Best regards,
Zelin Zhang

Dear Zelin Zhang,

I think this makes perfectly sense if you want to simulate an uniaxial compression test. If the sample is put under precribed deformation in z-direction, it will typically expand into the other directions. Sometimes, there will be no force outside the sample working against this lateral expansion, so you would assume a zero stress in x- (and y-) direction. If the sample is bigger and you simulate only small part of it, it may also make sense to assume some non-zero pressures in x and y-direction.

Contrarily, prescribing an elastic strain in more than one direction would not make much sense because it does not correspond to any type of typical experiment.

Bernd