Modeling Interference Fits

[ptc-708002]

Is it possible to model interference fits between a shaft and slightly smaller hole in Mechanica? I'm primarily interested in the final dimensions of the parts after assembly as well as the induced stresses. I took a Mechanica class last summer and the instructor seemed to think the software could do it but neither he nor I could make it work.
This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.

[saurav.gupta]

I think you can do this Pro/M by adding contact region on cylindrical surface of shaft and hole. Please make sure there is enough interference in the body for Pro/M to realise contact region. In addition, try to add free interface for shaft and hole top/bottom surface to avoid node merging when doing AutoGEM. Once you have done this, you can run the static analysis including contact region after applying Global Temperature load of '0' (as static analysis will not work without Load). Please make sure that CTE of '0' is assigned for the material property for entire assembly . I think this would give you the stresses you are looking for.

[ptc-708002]

Thanks for your reply Saurav. I just ran a very simple interference model (1" OD shaft x 4" long centered inside a .9985" ID hole x 2" long). This amount of interference is typical of my real-world applications. I used contact elements between the shaft OD and hole ID and constrained the top of the shaft far from the contact area. I used your suggestion of zero CTE and global temperature load. In the static analysis, I used single pass adaptive and localized mesh refinement. What happens is I get the following errors while running the analysis: Warning: Nonlinear contact solution did not converge. This is likely due to a modeling error such as incorrectly defined contacts. The analysis is proceeding with the best solution found. *Contact Area: 1.08106e-01 The contact area is non-zero for zero load factor because there is initial interpenetration (interference fit) in at least one contact region. Calculating Disp and Stress Results (10:52:17) Load Increment 1 of 1 Load Factor: 1.00000e+00 ** Warning: Nonlinear contact solution did not converge. This is likely due to a modeling error such as incorrectly defined contacts. The analysis is proceeding with the best solution found. *Contact Area: 1.43759e-01 ** Warning: Contact area is small in comparison to size of adjacent element edges for one or more contacts for all load factors above marked with a "*". If you need pressure results near the contacts, use single-pass adaptive convergence and select Localized Mesh Refinement. I hope that this is just a problem with the way I set up the model and not a limitation of the software. Again, thanks for your response.

[saurav.gupta]

Hi Greg, Right now I m not infront of my computer which has seat for Pro/E. I will try modeling your example tomorrow and would suggest you what is to be done next. In the meantime you may try running MPA. I hope you have defined free inteface to avoid node merging. This has worked well so far for most of my cases. If you run into more problems then there is a way to do it in independent mode, where you mesh the parts seperately, then translate them back to assemble in the interference state. Thereafter, rerun the above analysis.

[ptc-708002]

Saurav, I have tried modeling using MPA and I seem to be getting the same kind of errors. I'm not very familiar with the free interface connection and wasn't able to apply them to the shaft ends. Below are my shafts modeled as a quarter section with symmetry. Will the free interface connection work where the ends are not flush? I'll do some searching around for using independant mode. I've never tried that before. Thanks, Greg