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Bolt Pretension – Strange Behaviour

    • tortju


      I have a pipe model with three flanged bolted connections:

      I have defined two load steps for which the first one is used to pretension the bolts (only by a force of 100 N). The pretensioning is then locked in the second load step. I have used local coordinate systems for pretensioning each of the bolted connections such that the pretension cutting plane is in the middle between each pair of flanges. This ensures that the pretensioning is not applied where bonded contact is defined. An example showing two of the pretensioned flanged connections:

      When running the analysis two of the connections seem to be unaffected by the pretensioning while the third appears to be stretched instead of pulled together:

      What can be the reason for this behaviour? I have tried redefining the local coordinate systems and going over the contact defininitions but with no luck.

      I am attaching a .wbpz-file in case anyone would like to investigate the model:

      (The loads in load step 2 can be disregarded as they are not part of the problem).


    • Mickle Palmer


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    • tortju

      Thank you!

      However, it would look even more professional if it worked as intended. Do you have any suggestions for how to achieve this?

    • Aniket
      Ansys Employee

      Are you using bonded contact between flanges? Ideally, it should be frictional.

      1. Underside of the bolt head to flange
      2. Underside of Nut to Flange 
      3. Nut to Bolt

      above three contacts should be bonded. Also, is your bolt shank cylindrical? If yes, simply take an imprint of nuts on the bolt and apply pretension on the cylindrical face between nut and bolt head. This way you will not have to worry about coordinate systems definitions.


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