# Calculix sometimes converging

**URL:** <https://calculix.discourse.group/t/calculix-sometimes-converging/4103>\
**Category:** Model setup\
**Created:** [September 8, 2026, 7:42am UTC](https://calculix.discourse.group/t/calculix-sometimes-converging/4103 "2026-09-08T07:42:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Mishal](https://avatars.discourse-cdn.com/v4/letter/m/f17d59/32.png) [@Mishal](https://calculix.discourse.group/u/Mishal)\
**Post date:** [September 8, 2026, 7:42am UTC](https://calculix.discourse.group/t/calculix-sometimes-converging/4103/1 "2026-09-08T07:42:19Z")

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Hi Guys

Please refer to the link for the .inp file.

The simulation presents a connection where one location has a slotted hole. I am applying a fairly low pretension of 8kN on the bolts over 3 seconds, there is then 2 seconds where nothing occurs, and then I apply an incremental moment to the system for the next 7 seconds.

I am finding that the model will sometimes solve and other times not solve. I initially thought this may be an issue with using 8 cores for the simulation, but I got similar results using 1 core. Using PlastiX I have also set the PASTIX\_MIXED\_PRECISION to 0 and the issue still presists.

Has anyone experianced something similar or knows why I am having this issue?

> **[CCX connection - Google Drive](https://drive.google.com/drive/folders/1ocl2SgrLtCrzymSwqmS6wQ2C3lqlE1lx?usp=drive_link)**

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<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [September 8, 2026, 9:20am UTC](https://calculix.discourse.group/t/calculix-sometimes-converging/4103/2 "2026-09-08T09:20:19Z")

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Abaqus doesn’t want to solve this because of an overconstraint between pretension section and tie constraints. You should add contact there and only tie bolt heads/nuts if necessary.

Without this tie constraint, Abaqus reaches 6.52 s before diverging. However, adding BCs to all DOFs of the reference point apart from the one with moment makes it run to completion, also in CalculiX.

```auto
*BOUNDARY
14377, 1, 3
22674, 2, 3

```