Doing too much with too little knowledge. 2

[castleMadrid]

Does this work in WB?
All I just need from you guys is to tell me whether I am doing nonsense here or if otherwise—I just need to learn how to do it.

I have an assembly in WB of 7 parts (every part with defined contacts, some are auto-assigned, some I simplified by taking away unused surfaces) and 8 bolts (two of which are with bolt pre-stress).

The “solution” setup is as advised by cbrn on thread569-183819. (Large Defl., time steps, etc.)

1. I tried to run with all contacts bonded. It ran for few hours with no problem.

2. All contacts “no separation” with “Never update stiffness”. It ran for quite longer with a warning “weak springs added to converge to a solution”.

3. Like (2) above but with one of the contacts “Update stiffness >> Each equilibrium iteration”. It run for the whole day and did not converge to a solution.

 

[cbrn]

Hi,
sorry, but first of all when using Contacts in Ansys (WB or Classical it doesn't matter) you'd better have read with extreme care all that the help manual says about them.
Secondly, you have to be aware of the physics of your problem and not dumbly apply "things" that were possibly valid for others and not for you. In the setup you recall from my advices in another thread, for example, are you sure that YOU need large deflection? As for the time steps, as a second example, the thread you mention had an "impact-type" problem, or more generally contacts where the cont/surf were alternatively in open and closed contact: are you sure this applies for you? (I have no idea of your assy, but from what you describe I strongly suspect not...)
Do you have a clear idea of when to use "bonded", "no separation", etc etc? In fact, the difference btw your case 1 and 2 is that in 2 you allow sliding: I'm about sure that you have incomplete constraints on your model, or the sliding in reality would be carried by the contact itself, but then the choice of "no separation" is absurd because it has no friction.
My advice is to give another read to the manual and let us know if it ameliorates your situation...

Regards

 

[gurmeet2003]

castle,

I am going to answer part of the problme posed by you. When you bond all the parts togather and run your model, only one part of the assembly has to be constrained with respect to the ground. However when you use no-separation contact, the parts are free to slide, but can not separate. Therefore some of the parts may be undergoing rigid body motion, leading to comment about addition of soft springs. Work bench will automatically add soft springs to the model to prevent rigid body motion, when required. However it gives a warning to that effect. You need to make sure that soft springs are really 'soft'. You can do this by looking at the force developed in these springs.

Gurmeet

 

[castleMadrid]

One part is grounded and I thought it is possible just to rely on the bolts' contact, underneath their heads and around thier shanks, for the stability of the connected parts.

Thanks a lot

 

[cbrn]

Hi,
yes, indeed you can, but you must ensure that you use a contact formulation which will take the frictional force into account. And, if the externally applied force is higher than the maximal bearable one without sliding, that there is "something, somewhere" that will stop the forced part to fly away: it can be the bolt shank against the hole, of course.
To cut a long story short: it seems there is only one formulation adapted to your case: "frictional" (or "bonded", but not realistic when speaking about bolts...).

Regards

 

[castleMadrid]

Thanks Brian,

All the while I was thinking that I can use frictionless contact on my bolt heads since I have contacts at the shanks. It now works without contacts on the shanks but "Frictional" on the heads and nuts.

That's a great help. Cheers