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Where to put constaints to do FEA on thread

Where to put constaints to do FEA on thread

Where to put constaints to do FEA on thread

Attached is tie rod dwg. I am trying to do a FEA on the tie rod but results was not what I wanted.

Anyway, I will start by explaning this tie rod. There are four tie rod that hold two platen in place. The picture shows half of a tie rod cuz I used a symmetric constraint on it.

It has thread diameter of 9 1/2". So just using basic calculation with 825000 pre load on the tie rod. The stress should be around 12500 psi. But using FEA software (creo), the lowest stress I get by changing the constraint is 52000 psi. that's way too much for the material. I am wondering if I constraint it correctly.

Here is how i constraint it, I created a region where the nuts thread contact with the tie rod thread, I put the 825000 lb on this region on every thread.
Then on the opposite side of the thread (across from the above region, ie the slope part of the thread) I put a displacement constraint of tiying doen XYZ translation.

I am not sure if that's enough or can someone explain to me how to constraint a thread.



RE: Where to put constaints to do FEA on thread

You might ask in the Creo forum.

You might also ask yourself, when it comes time to actually make and use the tie rod, how you get a nut to engage those threads in the middle of the rod. It reminds me of the original design for the Hyatt Regency Kansas City.

Mike Halloran
Pembroke Pines, FL, USA

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