Internal stress does not affect mechanical eigenvalues.

Hello,

I am trying to use "Initial Stress and Strain" in Solid Mechanics to tune the mechanical frequency of a (doubly-clamped) micro-beam.

I am trying to use "Pre-stressed Eigenfrequency Analysis" which lets the beam relax then should use this as the linearization point for calculating the eigenfrequencies.

This technique works okay in 2D but not for a 3D model. No matter what I apply to the "initial stress and strain" tensor, I cannot change the eigenvalues. I do know the stationary solver is working; adding stress does change the displacement in a sensible way.

Is there a solution to this? Is it a bug? Enclosed is what I'm looking at.

Thanks in advance,
Jack