Simplified bolt connection with beam element, rigid constraints and thermal pre-load

General Questions
1

Hi all,

I have set up a thermo-mechanical model with two screws (Beam Element B32, diameter 4 mm) connected to the bore wall via rigid body elements, with contact defined, and I am simulating a preload using temperature. (Inspired by link)

It works, too; my manual calculation yields a prestress of 6386 N at a temperature difference of 220 K. However, the FE result is 2470 N (Reaction Forces)

Thermal Preload
Screw Diameter 4 mm
Screw Area 12.57 mm2
E Modulus 210000 N/mm2
alpha 1.10E-05 [1/K]
delta Theta 220 [K]
epsilon 2.42E-03 [-]
sigma 508.2 N/mm2
F 6386.2 N

beam32_preload.pmx (4.0 MB)

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image1622×890 162 KB

I think it has to do with the post processing of the data, i have tried section forces and total forces but both were not reasonable.

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2

You don’t have to use coupled analysis, it can be regular static step with *TEMPERATURE defined field.

In Abaqus, I get the following section forces for the same model (just using static step):

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image524×507 29 KB

It might be due to hinge-like behavior of such beam-rigid body connections in CalculiX: Simplified bolt connection with beam element and rigid constraints - #100 by FEAnalyst

3

When i use a static step and define two very different initial temperatures:

  • Bolts: –200 °C

  • Structure: +20 °C

the results doesn’t look reasonable.

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image1447×1143 240 KB

beam32_preload_static.pmx (3.8 MB)

4

I was rather thinking about defining it this way:

beam32_preload_static_mod.pmx (804.4 KB)

5

Thank you for your input, the Reaction Force is about 115N and i would expect something around 6380N. Am I doing something wrong during the evaluation of the results?

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image1385×852 158 KB

6

This is most likely the issue that I’ve mentioned before - hinge-like behavior of these kinds of connections. Run a frequency analysis and you should see it. The same model provides reasonable reaction forces in Abaqus where this issue is not present (due to proper implementation of rotational DOFs, MPCs and beam elements). As a workaround, you could try with 3 beams per bolt as shown here: Simplified bolt connection with beam element and rigid constraints - #100 by FEAnalyst

But, to be honest, if you check other related posts on this forum (especially the recent long discussions about bolted joints), you will see that beams are not really recommended for bolt modeling in CalculiX due to various significant limitations. In fact, it’s pretty much always easier and better to just use simple solids (cylinders) instead.

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