[niallmcgoo1304]

Hi I'm new to ANSYS software and this forum. I'm doing a project where I have to calculate the insertion force and retention force of a snap fit connector. I have set up a non-linear problem with a non linear material where the snap moves into a locked position. Im using displacement to move it (I cant figure out how to use a force yet) and I haven't a clue how to get insertion or retention forces from it.

Please any help greatly appreciated.

Thanks Niall

[jbreunig]

Is there a reason to use displacement rather than force? My first inclination would be to use a ramped force on the button. You can then plot force and displacement over time to see when the button snaps. That's just how I'm thinking of it.

If you still want to use displacements, then if you have a contact region setup, you can use a contact probe tool to get the contact forces. There's also a force reaction probe that might be of use to you.

EDIT: I now see that you tried doing the input force method, but weren't able to. I still recommend using the probe tools. It's meant for what you're doing. And IMHO you're correct to do a Non-Linear analysis.

[Gweher]

Well Jim, in my opinion using a force as an input is not a good approach as what he’s looking for is a force as an output quantity and not an input one. Plus in this case the model will be more robust if you define the displacement from the “free” position to the “locked” position and then proceed to the pull out for the force estimation.


You have several options to solve your problem. For the insertion /pull out simulation I would suggest using either a static structural analysis (without or with CE depending on your geometry) or a slow dynamics using a transient analysis. The analysis systems you choose depends on the geometry you want to model, for instance if you have a gradual slope between the two parts you can use a simple static structural system.


I would suggest starting with surface model to reduce the simulation time (take a slice of your 3D geometry).


If you give some additional inputs I can help you out and guide you through the process

[jbreunig]

Originally Posted by Gweher

Well Jim, in my opinion using a force as an input is not a good approach as what he’s looking for is a force as an output quantity and not an input one. Plus in this case the model will be more robust if you define the displacement from the “free” position to the “locked” position and then proceed to the pull out for the force estimation.

Maybe I wasn't clear. I was just offering how I would have done it. It's quick 'n dirty. When the snap closes, look at the INPUT force, and that's the force required to close the snap. Cheap 'n easy.

Also, perhaps you didn't see the remainder of my post. ANSYS has probe tools meant just for this type of analysis. Wouldn't it be easier to use the probe tools than to try to re-create the whole analysis?

[Gweher]

Well if it’s just a rough estimation he can directly estimate the force by hand calculation (snap contact angles, depending on the geometry complexity of course). The ramping force approach as you suggest could do the trick as a quick estimate but you also need to properly define your force increment. It’s not a huge additional effort nor computational time to have a proper time history of the force for the overall insertion / pull out process.

[jbreunig]

Agreed. His method of doing displacement is more accurate than force input method.

Grabbing the forces using the probe tool is probably the best way to do it. Here's some guidance the OP may find useful.

https://www.youtube.com/watch?v=WLwZ_9WCRSQ
https://www.youtube.com/watch?v=t-QeuIxJ40Y

And about transient forces
https://www.youtube.com/watch?v=tQIXYzFHXag

[niallmcg]

Hi

I lost my password and set up a new account.

First of all let me say, Thank you both soooooo much for your help and input. I appreciate the help from both of you so much. Thank you.

[niallmcg]

I am trying to apply a small force to the snap/cantilever a, but all these errors are appearing. Please help.............

An internal solution magnitude limit was exceeded. (Node Number 51, Body Cantilever (a), Direction UX) Please check your Environment for inappropriate load values or insufficient supports. You may select the offending object and/or geometry via RMB on this warning in the Messages window. Please see the Troubleshooting section of the Help System for more information.
The solution failed to solve completely at all time points. Restart points are available to continue the analysis.
The unconverged solution (identified as Substep 999999) is output for analysis debug purposes. Results at this time should not be used for any other purpose.
Large deformation effects are active which may have invalidated some of your applied supports such as displacement, cylindrical, frictionless, or compression only. Refer to Troubleshooting in the Help System for more details.
Although the solution failed to solve completely at all time points, partial results at some points have been able to be solved. Refer to Troubleshooting in the Help System for more details.
For more details, please see the ANSYS Performance Guide which is part of the ANSYS Help system.
Solver pivot warnings or errors have been encountered during the solution. This is usually a result of an ill conditioned matrix possibly due to unreasonable material properties, an under constrained model, or contact related issues. Check results carefully.
Contact status has experienced an abrupt change. Check results carefully for possible contact separation.

[niallmcg]

Ps.

Im literally a beginner, I only know how to do a static structural barely. If I uploaded some of my conditions could one of you maybe take a quick look????????? I would be so grateful of your help. Thanks

[jbreunig]

I'd recommend youtube to learn what you need to do.

If you've never operated an FEA program before, then you may want to start with the user manual. You can access the manual through the ANSYS customer portal.

Unfortunately, I can't help directly. This is a CFD forum, so you may want to try something a little more specialized for FEA.

[Gweher]

You can post process the result and identify the problematic area, in your case node nb 51. If you use RMB you can select the node by id number and see where it’s located.


A hint in the solver output file concerns the contact definition, how did you model it, with which formulation. It can be caused by different factors, but to identify the problematic areas you can plot the N-R residuals which show the force imbalance. An option would be to change the contact definition, and manually “help” the software. For instance the Detection method of the contacts is by default Gauss point (default “program Controlled”) you can change it to “Nodal-Normal to target” which often solves the problem. If that doesn’t work you can also reduce the default contact stiffness to a smaller value say 0.5 or 0.3.



If that doesn’t work you need to provide more details cause it’s a bit difficult to solve the problem with a little amount of information.