Hi there,
I am looking to use a non-linear mechanical analysis to determine the effects of flange misalignment under bolt pre-load. I am making use of the new bolt-preload BC (a nice addition!) and physical contact definition between the washer and flange faces. I have an initial gap between the washer faces and the flange faces, which I had assumed would be closed under pre-load. However, I am getting the below error when trying to run the model, which suggests this initial gap may be an issue. I think I’ve de-bugged any chance of rigid body motion, so am assuming it is this gap which is the issue.
A couple of questions:-
Is there any way to avoid this issue?
If not, can a contact pair initially be in contact only via a point rather than full surfaces?
Project link is SimScale , and the model in question is the dynamic analysis (albeit I tried in static as well with the same issue).
Regards,
Jack
Hello Jack, and welcome to our Forum!
Just wanted to let you know that I am actively looking into your case, and I will come back when I have a solution for the simulation.
Thanks for your patience.
Hi Again Jack,
I was just able to complete the simulation, you can find my copy at the following link:
The problem with the simulation is that at the preload step, the slope makes the bolt slide and the friction created by the point contact is not enough to keep it into place. The solution was to add another physical contact between the bolt shank and the flange holes.
Another important point is the elastic supports. The value you see in my setup is enough to constraint the bolts.
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Hi there,
Thank you for the quick response. I hadn’t checked the elastic support co-efficient magnitude, so this is a good tip.
Regarding contact of the bolt shank and bolt hole, in the actual physical set-up I would assume the bolt pre-tensioning would be such that this contact need not actually occur (i.e. the bolt is held such that contact is avoided). I’m wondering if applying a constraint to displacement in the Z & X directions on the bolt head and nut head would prevent this? Then the pre-load simply tensions in the Y direction, and the fact that point contact is not sufficient to hold the bolt need not be an issue.
I suspect also the mesh needs refining, as where the contact seems to occur is at specific elements, as opposed to a full surface.
I notice that you also changed the contact method to ‘Penalty’ as opposed to ‘Augmented Lagrangian’. Was this motivated by any particular reason?
Regards,
Jack
I also just picked up that your changes removed the Z-direction displacement constraints from the sides of the flange. I had included these as this model is to represent a small segment (< 3 deg) of a full circular bolted flange. I’ve just completed a run with these in place. I think they should be included, but am open to hearing thoughts otherwise.
Hi Jack,
In my opinion, applying hard constraints to the bolts breaks the model, because then this constraints will take all the reaction forces, as if the bolts where externally supported by other part. It is too artificial.
Sorry I missed the Z constraint on the sides.
The penalty method tends to be more robust in the computation. The catch is that it allows some penetration, so one should be careful and adjust the penalty coefficients.
Thank you very much for the help, it’s been really useful. I’ve marked the query as solved. Look forward to continuing the conversation on further SimScale use.
Cheers,
Jack