stress acting on threads

[vscid]

I have a half-ring,1 inch in thickness, 2 inch wide and 7 inch inner dia (10 inch outer dia).
The ring has a slot cut in the middle of the ring, parallel to the axis of the ring and dimension all the way across the width of the ring.
The slot has a tapped hole in the centre through which a stud will pass and mount on a pipe.
I would like to calculate the stresses on the threads when i tighten the stud against that pipe.
I would like to know the thread breaking load.
What is a good way of FEA modeling for this?

Rgds

 

[GBor]

First, I must not fully understand your geometry. A "ring" 2" wide and 7" ID should have an 11" OD, right?

Next, I would say this is probably better as a hand calculation...FEA isn't the right tool for everything, however, if it is FEA that you insist on using, I would probably concentrate on the hole and the fastener and do a 2-D analysis ignoring the rest of the geometry. If you are interested in thread breaking, model the thread profile for both the stud and the hole. Model additional geometry of the hole far enough away so that you can apply boundary conditions that won't impact the stress results at the threads (this additional geometry can be beyond what is really part of the ring, but you may find the non-linear stress redistribution may be impacted by this...hard to say without knowing materials and understanding the geometry a little better). Model the stud to the centerline and apply center line constraints.

Now you have to decide: Linear or non-linear analysis. This will ultimately be a non-linear analysis for more accurate stress results, but I typically run a linear analysis first to get an idea of how much load will be required. To do this, however, your threads from the stud and hole must be in intimate contact, which means you have to make some assumptions about thread engagement. Then, run a unit load on the bolt and compare the stress to the material yield, but this is where things get difficult. If you assume a limited contact at a single node, you will likely get a Hertzian stress that will approach infinity. I would recommend that you concentrate on the stress at the location where you belive the thread will break.

Once you have the stress ratio, you need to separate the threads and apply contact surfaces in a non-linear analysis. Then, ramp the load from 0 to the factor that you calculated from your linear analysis or maybe even a little beyond (since stress redistribution will likely allow your stud to carry a little more than the linear analysis suggests -- maybe as much as 30%).

Kinda' a lengthy suggestion...hope you understand it and it is useful, but in the end, the hand calcs will likely be faster and easier.

Enjoy!

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
Magnitude The Finite Element Analysis Magazine for the Engineering Community