Algor and threads
Algor and threads
(OP)
Hi,
I Have a rod with a 3/4"-16unc thread on each end that are 1" long , overall length about 13" with a 1.5" shoulder and fillets in the corners. My Question is about applying boundary conditions to it. One end is screwed into another parts and is "fixed" the other end has a 17,500lbf load applied in tension. the model is imported from Inventor 09 so the od's are threadless with the surfaces split-up. should the BC,"Fixed" be placed on the OD where the thread would be or on the very bottom face? or is there a better way to model a fixed threaded joint?
I Have a rod with a 3/4"-16unc thread on each end that are 1" long , overall length about 13" with a 1.5" shoulder and fillets in the corners. My Question is about applying boundary conditions to it. One end is screwed into another parts and is "fixed" the other end has a 17,500lbf load applied in tension. the model is imported from Inventor 09 so the od's are threadless with the surfaces split-up. should the BC,"Fixed" be placed on the OD where the thread would be or on the very bottom face? or is there a better way to model a fixed threaded joint?





RE: Algor and threads
RE: Algor and threads
RE: Algor and threads
My thoughts are that it may have something to do with poisson. If you pin the last row at the top of the threads, do you still get that high stress?
It sounds like you may have your own answer...if fixing the face is closer to a hand calculation, that may the right approach for your application.
You may also want to check in to 3-2-1 support methodology. The best paper I've seen on this is at www.roshaz.com, but the gist is that you use balanced loading and apply minimal boundary conditions to address rigid body motion and computing round-off differences. For your model, you would apply an equivalent load on the other end of your threaded rod and then pick three points where you would apply Tx, Txy, and Txyz at individual nodes.
The thought behind this is that boundary conditions are theoretically infinitely stiff, so load is going to go through them, but they aren't going to be able to "cushion the blow". You will get elevated stress levels around boundary conditions that may not be realistic.
RE: Algor and threads
Thanks.
RE: Algor and threads
To put some geometry to it: Txyz at the center of the end face. Tz in the thread area. This will allow Poisson's effect to displace the threads in the xy plane, but will move your stress to the proper location at the top of the threads.