Learning Forum

[Mariah Alves Pereira]

Dear ANSYS Community,

I am developing a Transient Structural analysis of a mechanical watch mechanism. One component needs to be elastically pre-compressed to fit into its assembled position before the transient motion starts.

I am trying to model this in a first load step with Time Integration turned off, to obtain the preloaded state before starting the transient analysis.

In its undeformed geometry, the component has significant interference with another part, as shown in the screenshot. It behaves similarly to a tweezer/flexible spring, with a pivot allowing rotation while both arms can move and deform.

I can obtain the expected deformation by applying a Fixed Support on one side and a force on the other, but this is not realistic. During the actual assembly, both sides can move while the component bends, so fixing one side changes the deformation behavior.

What would be the best approach to model this pre-compression while allowing both the rotation and elastic deformation of the component?

I have also tried an Interference Fit/contact-based approach, but so far I have not been able to obtain the expected deformation. I have attached a screenshot of the geometry to illustrate the problem.

Thank you in advance for any suggestions.

 

[peteroznewman]

Dear Mariah,

The best approach is to use two Frictional Contacts in the model, one on each end of the spring body.  During Step 1, with Time Integration turned off, the contact elements should push the tips to resolve interference with the other parts. I would also suggest that the model include a Revolute Joint at the pin-hole pivot of the spring.  Resolving contact interference at the tips may be challenging to obtain convergence.  Under Analysis Settings, set the initial substeps for Step 1 to a large number such as 20.  Editing the CAD model (or using Part Transform in Mechanical) to rotate the spring a few degrees clockwise would reduce the large interference on the thick end while creating a small interference at the thin end. This may be a more favorable initial condition to resolve the interference.