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Pretension in steps as linar static

Altair Forum User

Hello guys,

I'm modeling a wire rim with steel spokes and a composite ring with HW 14. Since the spokes (PROD elements) are under tension before any load is applied I use the pretension function with ADJUSTMENT. Goal is to get the spoke forces in a range of 1200 N +/15N and an even displacement around the rim.

Pretension with FORCE is not a solution, the forces of the spokes are almost equal but the ring is moving and the wheel gets eccentric. Also, I would need to use PBAR elements because the model would collapse.

Now my question, is it possible to do the linear pretension loadstep in steps without changing it to a non-linear-quasi-static loadstep? I stay way under the yield strength of 600 Mpa.

Thx a lot,

Felix

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Altair Forum User

Hi,

Since the spokes are in tension and forces in spokes are interal loads, you can go with preload option.

FYI

Altair Forum User

Hello Prakash,

thanks your your reply. If preload or pretension as subcase doesn't make a difference. Maybe I discribed my problem not correct.

The model is fine and works for the most part. But if the pretension is applied at once, I get uneven spokeforces. That is ok and pretty much what would happen in a real application, I just want the range to be smaller.

I think If Optistruct would appy the pretension in steps, the spoke force would be distributet more evenly.

Altair Forum User

I think If Optistruct would appy the pretension in steps, the spoke force would be distributet more evenly.

I don't see a direct way to apply pretension in steps, I will see if there is any work around to do this.

Altair Forum User

You can try this:

divide the pretension force & probably have multiple subcases and have PTFORCE in these subcases.

Altair Forum User

Hi Felix,

I think with 'pretension in steps' you mean to say that you want pretensions applied to different spokes sequentially.

In an automated assembly process, usually all bolts are pretensioned simultaneously. Sometimes, however, as you need, the tensioning may happen in sequence or in groups. In such cases, while Adjustment (change in L) is “locked” for bolts that have already been pretensioned, consecutive pretensioning force is applied to the next batch of bolts, which then become “locked” for the following step.

As mentioned, it is possible to construct more complex sequences of pretensioning, wherein some bolts have already been pretensioned (Step 2) while the next batch of bolts is being pretensioned (Step 1).

Important Note: Note that a specific tensioning sequence has an effect on the final result only in path-dependent problems, such as contact with friction or elasto-plastic materials, i.e a Nonlinear Quasi-static (NLSTAT) analysis.

Pretensioning Steps 1 and 2 require the solution of a static FEA problem. Therefore, Pretension and Statsub(Preten) commands can appear only in linear or nonlinear static subcases of the default NLSTAT type

The subcases with PRETENSION and STATSUB(PRETENS) can be used to create various sequences of pretensioning, such as tightening bolts in sequence or in groups.

In nonlinear path-dependent problems, this sequencing of pretensioning can be combined with continuation of nonlinear subcases, as controlled by subcase command CNTNLSUB, in quite arbitrary combination. STATSUB(PRETENS.

Regards,

Sandeep