Solved: Shock Response Spectrum - Bolt Connector Preload

Anonymous · ‎07-21-2021

Hello,

I can't seem to find an answer within the resources for this, apologies if this has already been covered.

For a bolt connector, during a Linear Static analysis, the correct beam stress is seen when applying a certain defined preload.

If the analysis type is changed to Shock / Response Spectrum, the preload stress is not seen in the results for the bolt connector. Is this the expected behavior?

Thanks

Anonymous · ‎07-21-2021

Further update.

Performing a shock analysis with 0 Newton preload returns sensible results for displacement and stress.

After a 10 Newton preload is applied to the bolt connector, some strange results appear, notable is the 33M displacement.

It seems there is an issue with Preloads in Response / Shock Spectrum?

John_Holtz · ‎07-21-2021

Hi @Anonymous

It looks like you are using separation contact between the bolted plates. Shock/response spectrum analysis does not support separation contact; response spectrum is based on a linear combination of modal frequencies. Separation contact results are nonlinear and cannot be added together. You might be able to use sliding/no separation. Otherwise, you need to make the contacts bonded.

Somewhere in the process, the analysis tries to calculate how much strain is needed in the bolt to create the specified preload. Without the separation contact, it provides garbage results.

John Holtz, P.E.
Global Product Support
Autodesk, Inc.

If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉

Anonymous · ‎07-22-2021

Hi John,

Understood. I've applied an automatic bonded contact, but there still seems to be a discrepancy in the bolt stress.

I've run Linear Static and Response Spectrum for the same case. For the Linear Static, I get the correct bolt stress from preload of 1Nm (approx 230 MPa) but for the Response Spectrum this is significantly lower (approx 1.8 MPa).

I've attached the relevant case files, could you confirm the issue or problem with the setup?

Many thanks