simulate pipe joint in Mechanica?

[RichardHorstket]

I want to simulate stresses in a pipe-threaded joint (1/4 NPT) in a cantilevered loading. I've done some studying, and apparently the highest stress occurs at the root of the last engaged thread, so I'm not going to get a realistic result unless I can simulate that interface. There's even a prestress condition at that exact location from torquing the joint. Is it even possible in Mechanica to represent any of this? I've tried working with simple assemblies before, and wasn't able to simulate interactions between parts. Any suggestions would be appreciated.

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[ckatsis]

Richard,

Mechanica can simulate contact between components of an assembly. So, in theory, you should be able to model in detail the threads of the connection and calculate deformations and stresses.

Christos Katsis

[RolandJakel]

Richard,

analyzing a threaded pipe joint in Mechanica with contacts should not be any problem, I've done several analyses like this in numerous projects for our customers.

But, I have to add that analyzing threads with contact is something for very experienced users, it's for sure no beginner's task. You have to know deeper structural mechanics and fastener theory as well as in advanced software functionality. At PTC in CER (Central Europe), we offer for our customers a special three-day workshop called “contact and fastener analysis”, which treats all necessary topics. If you have not the opportunity to participate to a workshop here, I attach two presentations that may help you to get familiar with this topic for yourself:

1) The_Mechanica_Wildfire_4p0_Contact_with_Friction_Feature_rev1p1.pdf: This presentation treats the theory Mechanica uses for contact analysis and shows you some application examples. The documentation is so detailed that you should be able to re-run the examples for yourself

2) VDI_Schraubenpaper_Jakel.pdf: A paper about “Numerical analysis of bolted connections with direct load introduction into the bolt head” I wrote five years ago, when still working for a different company. This is unfortunately written in German Language for a fastener analysis conference of the “Verein Deutscher Ingenieure” and a little bit outdated regarding Mechanica (today, you could solve the problem much more comfortable due to several software enhancements). But, it should show you what you can do with Mechanica. Also this paper is so detailed that you should be able to built up the model and rerun it.

If you work through these presentations, it should be no problem for you to analyze your threaded pipe joint.

Hope it helps,

Roland

[RolandJakel]

Richard,

just another remark: You write that in your application the highest stress occurs at the root of the last engaged thread. You'll find that this is the case my paper presented above for the nut, too. When writing the paper more than 5 years ago, I wasn't sure from where this effect comes, because usually at the university you learn that the first engaded thread is loaded highest, not the last. My guess was that the used friction free contact model caused this, because friction would prevent the nut from "putting over" and pulling the first thread out of the contact.

To provide the answer here: Even with "normal" finite friction (probably not with infinite friction) you will find this effect: At the conference where I presented the paper I met a guy from a bolt manufacturing company who could detect yielding of nuts at the last engaged thread(s) in experiments. So, this effect is really present and you will be able to simulate it with Mechanica.

Best regards,

Roland