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Angular bearing

Angular bearing

Angular bearing

(OP)
What is the methodology to analyze angular bearing?
1. What co-ordinance system should I use?
2. How to constrain inner, outer and the balls? (particularly the balls?)  
3. What contact should I use for balls and rings?

 

RE: Angular bearing

prym,

What are you trying to accomplish with your analysis?  Are you trying to design/optimize the components sizes or materials?  Are you trying to model behavior under dynamic loads?  Are you trying to get a rough factor of safety or detailed deflections?  Knowing your objective may help tailor our advice for you.

If you are simply looking at axial (thrust) loading, you could probably simplify your model by using radial symmetry (e.g. analyze a "pie piece").
However, if you are looking at unbalanced or dynamic loads, you probably need to retain at least half the model.  This means a lot more elements and contact surfaces, but it can be done.  In any event, I recommend using symmetry as much as possible (this will help with your constraints as well as decrease your model size)  

I expect that, whatever your objective, you'll be using a cylindrical coordinate system (r, theta, z).

With regards to constraining the balls, the contact surfaces with the races should be enough to keep them from "flying off".  But, if you encounter problems, I have found success with attaching weak ground springs.

Hopefully, some of this gets you started.  Feel free to feed back with questions or images and we can help you out.

Pete
 

RE: Angular bearing

(OP)
Hello PetieSmo
Many thx for reply

I will be trying to analyze contact behaviour and only in static mode, applying axial and radial forces and case hardened groove surface.
I have got few more advanced cases with balls but first I need to understand how to analyze simple radial or thrust bearing.

Regarding to 'weak ground springs' - I have never used that before. Could you tell me more about that? If you consider Radial Bearing and radial force to outer ring the ball could 'flying off' In reality there is a cage and the balls always stay at the same place - that could be the example that balls should be constrained in some way.

1. What contact type would you use between balls and races? Is it only interface contact?
2. Should I apply infinity friction in the 'contact'?
3. Does Infinity Friction stop moving balls from position?
 

RE: Angular bearing

prym,

As with any FEA model, the challenge/trick is to appropriately constrain the model in space without influencing the result.

I would suggest you begin with the simple radial bearing (cylindrical rollers), so that you can take advantage of planar symmetry.  (You will not be able to use symmetry for tapered rollers).  I would then suggest restraining the roller cage and the inner race in the Theta dimension.

For the outer race, there are probably different approaches depending upon how the bearing is constrained in real life.  For the purposes of learning, I would suggest you start by constraining the outer surface of the outer race in Theta & Radial (R) dimensions. (Note, with this constraint, the outer race will not expand/swell, which may be an OK approximation if the bearing is pressed into a very rigid plate/housing)

With regards to contact, I would only expect radial interface contact for the radial bearing situation.  If you set your default interface to "contact", you may save some time by not having to define each contact region separately (although, Mechanica may define many more contact regions than you would normally choose to define on your own).

To answer your question about 'infinity contact': This feature prevents two surfaces from sliding tangentially to one another when they are in contact.  Without knowing more about your application, I think it will probably help you to have this feature applied.  

I will save any description of weak ground springs for a future post.  Hope this helps.  Let me know how things go as you progress.  Send a picture of your results.

Peter

RE: Angular bearing

(OP)
Hello
The assembly finished with fatal error - I had to forget something
Could you have look - belowe is the messange and attached pdf (explaining what I did)

Fatal Error; Run Terminated
Wed Apr 28, 2010   14:57:48

The model is insufficiently constrained for the analysis.
Please review the element connections, properties, and
constraints. If this is a modal analysis, then you may
be able to obtain a solution by requesting additional
modes.

You may be able to locate your model's problem area by
using Mechanica database ID numbers. ID numbers can be
queried using the "Entity ID" macro in Mechanica
Standalone.  The following ID numbers are associated
with this error:

748466
776534
779656
876264
876384
876530
877256
877258
878178
878180
878428
878976
878978
880870
881504
881506
906308
906456

The unconstrained degree of freedom can be seen by running
a constrained Modal Analysis with rigid mode search.
Animating the rigid modes will display the unconstrained
degrees of freedom.  If the error still occurs, then the
issue could be caused by material properties or unattached
spring/mass idealizations.
 

RE: Angular bearing

Where is your symmetry constraint on the outer race?

 

Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com  

RE: Angular bearing

Also, as a technical point of interest the rotational constraints in the constraint dialog box are not applicable to solid elements regardless of the coordinate system of reference (e.g. cartesian, cylindrical, spherical).

Steve

Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com  

RE: Angular bearing

(OP)
Hi

I applied symmetry constraint on the outer race also but I just did not show it

I will remove rotation constrain  

RE: Angular bearing

A couple of questions:

1) Do you have contacts set up for each roller?

2) Do you have contacts setup for the inteface between the roller/inner race and the roller/outer race?

Steve
 

Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com  

RE: Angular bearing

(OP)
I have removed the rotation constrain  but there is still the same error?
Should I constrain rollers?  

RE: Angular bearing

What do you mean "only on one side of the bearing"?  Do you have contacts estabished on the outer surface of the inner race and the inner surface of the outer race?

Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com  

RE: Angular bearing

(OP)
There is 11 rollers, and using symmetry constraint we can see 5 of them so these 5 are in the contact with inner and outer race (so I have got 10 interface contacts)
I must be doing some big mistake because my any analyse with contact end up with the same fatal error and the same note.
EX. two block with interface contact between them, one is constrained and second has got applied force and at the end I have got the same note about 'The model is insufficiently constrained for the analysis...' and showing red mesh like above
 

RE: Angular bearing

Try simplifying the anlaysis to start with.  Remove all but one of the rollers.  Apply your contacts. Run the simulation.  If it works then keep adding rollers until you find the problematic roller.  If the analysis fails with only one roller, then you should be able to find the issue quickly in the simplified model.

You could also try posting a zip file of the model so that I could take a look if you still are having troubles finding the problem.

Steve
 

Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com  

RE: Angular bearing

prym,

Was on vacation for awhile - sorry i didn't respond sooner.  One thing that pops out at me - there is no Z constraint on the outer race or any of the rollers - this could be the source of your constraint issues.

Another possible issue - your load condition on the outer race is not truly symmetric.  You might try deleting the symmetry condition of the outer race and replacing with a constraint in R on the cut plane (permits the outer race to move along the Y axis, while maintaining radial continuity with the removed material).

Just a couple ideas.  Keep us updated.  Like seymours said, you can send us a file to play with, if desired.

Peter

RE: Angular bearing

(OP)

I am trying to analyze the same think but using very simple assembly and there is the same issue of course
Could please have a look on that assembly and check it what is wrong, it always shows the same error like on the attached picture
Could please set it up correctly so I would know for future how to do it?
it looks that there is mesh problem only but you may find something more perhaps
 

RE: Angular bearing

(OP)
I have just noticed that non-linear box is unticked and contact box as well!
Since I have got them 'on' there is no more mesh problem

RE: Angular bearing

(OP)
Hello

I am trying to analyze just 3 rollers and inner ring having 3 contacts set in the same way and there is a worning that:

1. Contact is not possible for
Contact: 360262

Contact is not possible for
Contact: 360264

One or more contacts in the model will
            have no effect because it is not possible for
            any of the elements on one side of the contact
            region to contact any of the elements on the
            other side. See the log file for a list of
            contacts for which this applies.


but when I finished analyze the result shows stress in all 3 contacts what means that contact was applied

Can anybody explain me this wornig?

There is mesh about 25000 elements and 0.5 mm in contact, all parts are tangent and i used 'infinite friction' in the contacts

RE: Angular bearing

prym,

How did you define your contacts?  If you defined them surface-to-surface, then i wouldn't expect that message.  If you defined your contacts as part-to-part, it's possible that contact definitions were created for other surfaces (e.g., the flat end faces).

Seems like you're starting to get on the right track with models of increasing complexity.  Good luck

Peter

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