Screw thread simulation with ansys

[Ignicolist]

Hi all!

I´m trying to simulate the tightening of a screw. It sounds easy, but I can´t get any result.

First, I have created a 3D file with a screw and a long nut (see picture).
The outer cylinder with the thread is fixed.
The plate between schre head and thread is also fixed.
The total tightening torque is given to the screw head.
Contacts:
Between screw head and plate: friction (u=0,2)
Between screw thread and cylinder thread: friction (u=0,12)
Between cylinder thread and plate: frictionless

I have also set a cilindrical support on the screw heat with axial and tangencia directions free.
The problem is divided in substeps, but I it is not working. Large deflections activated.
I have also attached the geometry.

I would appreciate a little help with this! Thanks in advance

 

[Ignicolist]

And the overview

 

[karachun]

Maybe your model is poorly constrained. Screw have some gap and bolt can rotate and translate in axial direction free. Fix rotations and apply axial force equal to bolt preload. Also maybe your mesh have bad quality.
Try to simplify problem.
1. Assume that threads are cylindrical, not helical. With this assumption, you can model bolt and nut in asymmetry.
2. After achieving solution in asymmetry you can model bolt in 3D with cylindrical threads. Symmetry plane can help to reduce model size.
3. And only after that, you can model bolt with actual thread geometry.
Nonlinear contact in FEA isn’t easy task, if this is your first project in FEA then I recommend you to start from Ansys tutorials for contact.
Link

 

[JGard1985]

Agree with karachun... even though it seems simple what you're asking ANSYS to do is really....really computationally expensive. You need a very fine mesh to ensure your threads are captured correctly with no penetrations. ANSYS also has to evaluate/assess contacts at every timestep which is exhasustive, since small elements drive smaller time steps.

You may also probably need an explicit time-history based solver vs. large deformation implicit solver to capture the motion

If you're interested in thread loads, I'd start with a 2D approximation (several examples online)



Jeff
Pipe Stress Analysis
Finite Element Analysis

http://www.xceed-eng.com

 

[L_K]

http://www.padtinc.com/blog/the-foc...s-in-threaded-fasteners-with-ansys-mechanical