Study Set Up

[JMirisola]

Morning all,
While I've done some Simulation studies in the past, they've always been straight forward studies. This time I need some help with the set up.
I have an 8" diameter rod threaded into a 1/2 tube with a 3" wall thickness. They are Acme threads at 1/2" pitch. There once threaded together, the rod will be welded to the tube as well. The question is whether the threads, and weld, will withstand 24,000 lbf. (FOS of 4). I did create the threads on the two pieces as I'm guessing that I'll need to create contacts between them, but I'm hoping that someone can tell me the best way to go about this.

Thanks!

Jeff Mirisola, CSWP
Design Manager/Senior Designer
M9 Defense
My Blog

 

[JMirisola]

I've attached a picture for a bit of clarification.

Jeff Mirisola, CSWP
Design Manager/Senior Designer
M9 Defense
My Blog

 

[kellnerp]

Jeff,

Have you considered running it without contact first? The reason to do this is simple, the weld is far stiffer than the threads and there is no clearance in the weld so it takes load from first application of the load. So it is likely that the weld will be the primary load path into the tube.

As to running contact on the threads you will likely have to make several runs to capture various tolerance extremes. Do you plan to have preload on the threads?

TOP
CSWP, BSSE

http://www.engtran.com

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[JMirisola]

TOP,
The preload, if any, will be minimal. It'll depend on how, ultimately, the rod gets indexed as the it's the last piece of a hinge assembly. However, the assembly isn't designed as we haven't determined that this threaded rod idea is going to work.
Does any of that make sense?

Jeff Mirisola, CSWP
Design Manager/Senior Designer
M9 Defense
My Blog

 

[kellnerp]

Well it makes sense as a boundary condition. Makes it really hard to do a valid FEA though. Consider that when you make the weld the thread could be floating without contact, bottomed in either direction. That is why I said the weld would likely be taking all the load.

Draw a free-body diagram of the various scenarios.

I am not sure why you would go to all the trouble of making an acme thread on something that is welded together. Threads are for things that might need to be disassembled. A taper or press fit with a weld makes a lot more sense.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[JMirisola]

Turns out, it's a moot point. We got the study to run and it fails, miserably. Thank God I'm getting on a plane tomorrow night for a few days R-n-R.

Jeff Mirisola, CSWP
Design Manager/Senior Designer
M9 Defense
My Blog

 

[kellnerp]

In what way did it fail? The simulation or the components you were analyzing?

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[JMirisola]

The components. The threads ripped out, theoretically. Back to the drawing board...when I get back from Boston next week.

Jeff Mirisola, CSWP
Design Manager/Senior Designer
M9 Defense
My Blog