When you have parts that come in contact with each other and there will either be expected strain or displacement, you can sometimes economize your study by using shrink fit vs non-linear studies. If you have a displacement condition, you may be able to get away with using shrink fit instead of solving a non-linear study, although every case is different.
This technical tip draws from a Simulation tutorial for large displacement. The goal is to demonstrate two methods you may be able to use when you have a problem involving contact and displacement. You can open the tutorial or download the modified version used in this tech tip below.
The objective is to look at the shrink fit (static problem) vs a non-linear contact problem, “large displacement” problems are not the focus of this article. The large displacement tutorial is only used as a model reference. You will need to evaluate whether you have a large displacement problem, and work with it accordingly.
From the “Help Menu/Tutorials” open the large displacement contact file set (downloading the modified files will be easiest since there were changes made to both configurations and studies).
Static Study With Interference
Notice how the two parts have interference (apps. 0.85 mm along the Y-axis). Use interference detection to evaluate the interference.
The Shrink Fit
When you have interfering parts and you need a study to show information about stress, displacement, and strain you can use a shrink fit to accomplish this. Geometry can be a constraint of having the option to use a shrink fit (vs doing a non-linear study), but many times it can be a good alternative because it is available in Simulation Standard (included with SOLIDWORKS Premium), and it generally runs much faster than a non-linear study. Special contact conditions and large displacement can however sometimes create a need to use a non-linear study (even with large displacement turned on for the static study). The static study with shrink fit does enforce contact, but through the function “shrink fit”. You do not have to set up additional no-penetration contact sets.
Shrink fits are special fixtures available for static studies only, and as with most Simulation studies you will want to pay attention to mesh quality, high or low displacements, and incompatible mesh conditions (the SOLIDWORKS Help is usually very good at discussing how to set up your study for the best results for these mesh related issues).
Non-Linear Set Up Difference
Whereas the static study begins with the two parts in interference with each other, the non-linear study begins without interference but in contact. A reference fixture is added to move the slider in the X-axis for 10 mm which develops the same final position that the static study uses.
Both studies were solved using draft mesh, and you can see there is a big difference between a static and non-linear contact problem (24 seconds vs 3 minutes and 24 seconds).
You can see from the Y displacement plots below that the results are nearly identical (Static study w/shrink fit VS non-linear study with a moving part + no-penetration contact).
One bonus of running the non-linear study is that you can get intermediate results as the contact develops (see appendix 1 to download files and displacement videos).
Many of us may only think about shrink fit conditions when it comes to pressing pins into holes, but with Simulation Standard (Static Studies) you have the opportunity to use shrink fit for some situations where you ordinarily think you have to create an non-linear study. Shrink fit can be a “high value” method of cheating a contact problem down to a set up that is very simple and quick, and is a good tool to keep in your virtual Simulation toolbox in your daily simulation strategies.