Clarification on Periodic Boundary Conditions

[Raghunandan Pratoori]

Hello,

I am trying to apply Periodic Boundary Conditions on a cubic sample in all the three directions and then compress it - compression of an RVE.

The displacement I need to give is:

For this, I first applied PBC using DoFTools::make_periodicity_constraints and then added displacement to the corresponding DoFs (selected them using DoFTools::extract_boundary_dofs) using constraints.set_inhomogeneity.

I have a few questions regarding this -

1. Am I doing this correct?

2. Also, do I need to specifically restrict rigid body motions? If yes, what is the best way to do this? I tried by fixing some nodes, but it is becoming too artificial and causing huge distortions at higher strains.

Thanks in advance,

Raghunandan.