Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

How to take acount of residual torque and force for screw/nut in FEA?

How to take acount of residual torque and force for screw/nut in FEA?

How to take acount of residual torque and force for screw/nut in FEA?

I work on a shaft which is taking a part sandwiched between a nut and the shoulder of thus said shaft.
Before installation of the shaft into an assembly, the nut is torqued at 75 Nm.
Once the nut screwed, the torque of 75 Nm is relaxed. So the equilibrium of the nut is as follow :
  • An axial clamping force between the shaft shoulder and the nut flat surface
  • A residual torque which is there because of the thread friction
The clamping force is calculable with screw calculations.
However, how to calculate the residual torque?
How to put this residual torque in the FEA since it is only concerning the interface of the threads?
Joel Lapointe

RE: How to take acount of residual torque and force for screw/nut in FEA?

Depending on the complexity of your model, you probably could include the thread in the geometry and simulate the screwing process so that all residual stresses are automatically considered in the analysis with actual loading.

RE: How to take acount of residual torque and force for screw/nut in FEA?

I have frankly never heard anyone ask about "residual torque" beofre. Not in 40 years (god, that sounds a long time).

Why is "anyone" doing FEA on a nut ? Nuts (and screws) have defined allowable loads. What's the concern ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: How to take acount of residual torque and force for screw/nut in FEA?

rb - maybe they are a squirrel (sorry, couldn't resist).

Modelling the threads of a bolt/nut is, at best, a nightmare.

I have seen bolt preload modelled by using an initial temperature change with material CTEs. But it still takes a lot of "sorting out"

RE: How to take acount of residual torque and force for screw/nut in FEA?

I did a small study on some weld studs. In the field some were fracturing from fatigue and it wasn't clear why. The claim was that they were over-stressing them in tension somehow.

My hypothesis was that the good ol' boys in our World Class Factory, were just grunting the nuts in place and paying no attention to the torque specs, which might be OK, if item was remaining in place.

So I had them weld up a bunch of studs to a plate and I got the nuts and started some twisting of my own, ti see if they snapped off just from tension.

What I found was that, if one just didn't stop turning the nut, the stud would elongate until the pitch on the threads was too much to fit in the nut. On the first install that would be no problem as the stud would have the full pre-load, but on any subsequent install the nut would hit the end of where the threads were good, the torque would shoot up, and the joint would not have the expected pre-load, allowing the part to shift back and forth until the stud snapped off.

What I didn't see, up to the point where the thread stretch was too much to fit anymore, was the body of the weld stud twisting. Maybe there is a tiny amount, but it doesn't seem consequential. For certain there is friction with the nut and the thread and the nut and the part and that friction will retain, for some time, the torque according to the amount of friction. But if the nut/screw unwound to remove that torque I doubt there would be a noticeable change in stress or pre-load and will be below all other contributors to variability.

In any case the residual torque cannot be more than friction at the screw thread radius can provide.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close