Learning Forum

[pgaspic]

I'm having repeated issues running a prestressed modal analysis on a suspension rocker with dummy bolts and spacers.

As you can see in my setup, I am applied a force to the middle spacer, which is mated to a bolt via a No Separation contact. This force is then reacted by the two other bolts, which are setup in the same way, however completely fixed in all 3 DoF.

What concerns me is that I'm getting really weird deformation at the loaded bolt, as it seems as though the bolt-hole is not deforming with the bolt.

Any advice on how I should go about correcting this?

[Gaurav Sharma]

Few potential checks that can be performed are:

1. Are the preloads and the perpendicular force on spacer applied sequentially or if both are applied simultaneously. Usually the prelaod comes first and the other forces follow it in load step-2 while the preload is locked. You may like to run another iteration for testing purpose by suppressing the sideways force. This shall reveal if lateral force is the culprit or if pretension alone is also leading to ambiguous results.
2. Force balancing - You may also check the force reactions at the head and nut side of the bolt and understand how the preload and lateral force is getting transmitted to the adjoining component. This may help identify if some contact is not working as expected and need intervention. It may also be worth checking if the boundary conditions are getting some unexpected reactions.

[peteroznewman]

A couple of basics about Modal analysis is that deformations are scaled so the value of the deformation is unimportant, only the shape of the deformation and the frequency are relevant.

It seems the No Separation contact between the bolt and the spacer allows the bolt to rotate which results in an expanding bolt head deformation.

It might be best to replace No Separation with Bonded Contact.