# I am seeing some strange CPRESS results

**URL:** <https://calculix.discourse.group/t/i-am-seeing-some-strange-cpress-results/486>\
**Category:** Uncategorized\
**Created:** [March 14, 2021, 3:12pm UTC](https://calculix.discourse.group/t/i-am-seeing-some-strange-cpress-results/486 "2021-03-14T15:12:21Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![LukeR](https://avatars.discourse-cdn.com/v4/letter/l/9de053/32.png) [@LukeR](https://calculix.discourse.group/u/LukeR)\
**Post date:** [March 14, 2021, 3:12pm UTC](https://calculix.discourse.group/t/i-am-seeing-some-strange-cpress-results/486/1 "2021-03-14T15:12:21Z")

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I have a model I have built that is giving me some strange CPRESS stresses, (my first proper Calculix model but I am coming for quite a bit of experience with Abaqus although it has been a couple years since used it every day)

This is created and post processed in PrePoMax, I have not tried to postprocess the results in any other software yet which should probably be my first step if I had anything else installed 🙂

This is a cam/piston lock mechanism. It is basically an an offsent pin turns in a slot and drives a piston which moves linearly. It took a while to get the model running correctly but it does what I expect now although it is a bit large and takes 12 hours on my fairly powerful computer. (this is run 17 so I have been working on it off and on for a while 🙂 I forgot to request the reaction force on the rotation BC on the pin but will do that next time I run it.

The attached pictures show the issue. The cam pin is slightly (0,02mm smaller than the hole it is in) and I think I have contact adjustment turned off. At the step shown in these pictures there should be near zero load as the cam is just rotating a few degrees and is not yet touching the slot wall. If I plot load on the cam surface or load on the working end of the piston there is no real load at this point but I see these very high stresses all around the bearing ends of the cam pin.

thanks

Luke

 ![strange_cpress](https://global.discourse-cdn.com/free1/uploads/calculix/original/1X/12d831a5d208d2bfd6d619b94200be370c3c87fe.jpeg)

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**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://calculix.discourse.group/u/Matej)\
**Post date:** [March 15, 2021, 9:25am UTC](https://calculix.discourse.group/t/i-am-seeing-some-strange-cpress-results/486/2 "2021-03-15T09:25:35Z")

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Dear Luke,

it might be something wrong with the PrePoMax so post-processing in another software is the first step.

The other reason could be the mesh. When the mesh is created, the cylindrical surface it turned into a polygonal surface. For the solid cylinder, the polygonal surface is inscribed into a cylindrical surface making it smaller. Similar goes for the hole.

Did you use a node to surface or a surface to surface contact?

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<div class="post-metadata">

**Author:** ![LukeR](https://avatars.discourse-cdn.com/v4/letter/l/9de053/32.png) [@LukeR](https://calculix.discourse.group/u/LukeR)\
**Post date:** [March 15, 2021, 2:11pm UTC](https://calculix.discourse.group/t/i-am-seeing-some-strange-cpress-results/486/3 "2021-03-15T14:11:09Z")

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Thanks Matej  
I used Surface to Surface interaction without adjustment.  
The holes are 0,02mm over size (on a 10mm hole), perhaps I should have made the holes a bit larger.

I need to get my Linux machine and try some other post processing.  
Luke