Stress concentration at the volume discontinuity

[R.Gillen]

Hello,

I have a problem with modeling a rod-shaped solid volume with a breakthrough.
Basically, I have three volumes that together form a rod-shaped component. These are referred to below as the left, middle, and right volumes. This division was chosen in order to be able to use a volume mesh refinement in the area around the hole in the middle volume. The hole in the middle volume is cut in using a Boolean operation.
Now to the problem: when I then calculate the model, there are stress concentrations at the contact surfaces of the volumes that should not actually be expected there (see image 1 - bending stress for illustration).

Now to the hints and possible solutions:

1. Without the hole, there are no problems
2. The contact surfaces of the touching elements are defined by the same lines and thus lie exactly on top of each other.
3. As soon as the middle volume is provided with the hole, the FE mesh of the left or right volume no longer matches that of the middle volume (see image 2).
   
   
   
   It seems that as a transition between the two mesh sizes, there is only a line mesh refinement around the end face of the left or right volume. A manually specified surface mesh refinement such that both FE meshes fit together at the contact surfaces makes no difference.
4. (And maybe also relevant: after cutting the hole, some nodes and lines are merged/deleted)

I hope I have described my problem somewhat understandably.
So how can I ensure a clean force transmission?

Thank you very much for your help in advance.

[stefan.hoffmann]

Hi R.Gillen,

Thank you for your message and welcome to the community!

Please check how your result smoothing is set. Have you also switched to Continuous within all volume bodies here?

https://www.dlubal.com/en/downloads-and-info/documents/online-manuals/rfem-6/001104

To analyze the problem more precisely otherwise, the model file would be very helpful:

Click on File → Save As and select the following settings to reduce the file size:

Then upload the file here (e.g., *.rf6, *.rs9) – this way the community can also contribute to the solution.

Do you not want to share the file publicly? No problem – send it to me via direct message: click on my profile picture or my username → Message.

Best regards
Stefan Hoffmann

[R.Gillen]

Thank you very much for the reply,

I have meanwhile found a workaround by inserting a short intermediate volume with volume mesh refinement at the problem spot. However, this only circumvents the problem and is not a real solution.

Therefore, I am attaching the file here:
Balken mit Durchbruch.rf6 (1.6 MB)
Brief explanation of the model:
Looking in the negative Y direction, from left to right there is the workaround, the problematic component, a reference component without a hole, and a reference rod.

I had already unsuccessfully tried the solution with result smoothing in volume bodies.

Best regards
Ruben Gillen

[stefan.hoffmann]

Hi R. Gillen,

thank you for the model. I can understand it now. Due to your modeling, there are still overlapping surfaces that you need to eliminate.

So assign surfaces 11 and 16 to volume body 21 instead of boundary surfaces 47 and 48; delete surfaces 47 and 48:

Then everything looks as expected:

Best regards
Stefan Hoffmann