BOLT PRELOAD IN A MODAL AND FRF ANALYSIS

[Anonymous]

Hi to everybody,

I'm here to submit to all of you guys a question: Everyone knows that a preload can either change the natural frequency of a system or the frequency response function (FRF) to a sinusoid load. In my case the system is preloaded by means of a threaded rod. Screwing the nut it's possible to vary the axial force impressed by the rod on the structure. My question is the following: how could I model this event? I tryed with both solutors (Nastran and SimMech) but they cannot manage the "Bolt routine" and abviousely a punctual load is not permitted in a modal analysis because this kind of analysis studies the structure in case of "no dumping" and "no load".

Anyone could help me please?

[KubliJ]

Hi @Anonymous

I'm not sure I am following. There is modal with presstress analysis. I believe that should allow you to use the bolt preload. I think the big issue would be contact instead. The modal analysis isn't going to let you use surface contact. It will convert it from surface to bonded in the modal analysis. Depending on your setup, this will basically negate any bolted connections prestress.

This is the same for Simulation Mechanical and Nastran, both are not going to allow surface contact and only give bonded contact.

Thanks,

James

[KubliJ]

I am mistaken about the bolt preload, it is not allowed in Sim Mech. And applying a thermal contraction to the bolt manually to create the preload also does not seem to work either.

[Anonymous]

Thank you for your help but unfortunately nothing seems to work.