Bearing vs Force

[RichardOliver4462]

I have a model, and when I apply a bearing load to a lug get very different global results to a force of the same magnitude applied. I believe that this is only the case since the 2018 update...the bearing load seems to apply forces radially and not just sinusoidal distribution in the direction of the load.

I suspect that the application of a bearing load is not what I was expecting. For instance if one has a beam with a lug in the middle and fixed at the ends, applying a vertical bearing load  to the lug, to simulate a shackle pin does not give vertical reactions at each end of half the applied load. In fact the reactions vertically are very small and there is a large transverse load at each constraint.

Can you confirm, if either the bearing load application is not working correctly, or I have misunderstood the type of loading applied.

[esteffes]

I would suggest removing the ability to use the bearing load if it doesn't work, When I used it I was suspect and checked the values using both inventor professional FEA that still works and Ansys.  As for the verification manual, I don't think they have used it in some time, I started going through it and found files that are do not work.

I agree they should at least go back to the previous version or disable the commands if it doesn't work.

[RichardOliver4462]

Totally agree that this should have been disabled in the update following the error being found.

Users can not reasonably be expected to know which functions give reliable results and those that don't.

[David.Kind]

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@John_Holtz wrote:

Hi @David.Kind

I received your post, and we are working on a reply.

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@John_Holtz any update?

[Anonymous]

Actually I don't believe that this will be fixed before the new IN-CAD 2019.

We don't use IN-CAD 2018 due instability issues with the newes patch (several crashes with simple linear part simulation) and wrong bearing force distribution.

It is really unfortunate that a complete version of a product isn't reliably usable!

[John_Holtz]

Hi @Anonymous and everyone else.

The fix for the bearing load is scheduled to be released as part of 2018.2 hotfix 1 according to the release notes. As you may know from the thread Nastran In-CAD 2018.2 unstable, we are working on the kinks to get the hotfix posted to the download page.

[David.Kind]

@John_Holtz, to be clear, I'm interested in an update with respect to Autodesk's approach to quality on the Nastran-In-CAD product.

[Anonymous]

Hello @John_Holtz,

thanks for the update!

We are happy that a hotfix was released and will try 2018 in the next project 🙂

[Anonymous]

Nice to see that bearing load is now working in Nastran In-CAD 2018.2.1 and 2019 on the whole and has a new option to switch between "Normal To Surface" and "Components". Great so far. But there is still an issue with bearing loads at a cylindrical outer face. The load acts in the wrong direction with the option "Normal To Surface". The pictures should tell it all. With the Option "Components" it is working OK.

Model

Result

[David.Kind]

$10 says they tell you this is normal and consistent with the UCS (glyphs be damned).

[Anonymous]

Someone else any idea why bearing load is working in the wrong direction in Nastran In-CAD 2018.2.1 and 2019 using option "Normal To Surface"? Maybe @John_Holtz ?

[John_Holtz]

Hi @Anonymous

Thanks for the feedback. (Sorry it took me so long to try this out.)

I agree with your findings. I created a similar model so that I could test the bearing load on the outside of a cylinder and on the inside of a hole, like this:

These are the results that I obtained. I will report this to the developers.

Load direction	On shaft (outside)	In hole (inside)
+Y	Wrong	Okay
+X	Wrong	Okay
-X	Wrong	Okay
-Y	Okay	Okay

[Anonymous]

@John_Holtz

Hi John,

thank you for your investigation. Good to know that it's not only me. But I'm wondering why the bearing load on a shaft is working okay for you in one direction (-Y) and is not in all other directions. For me the bearing load on a shaft is working reverted in all directions if the option is set to "Normal To Surface" and is okay if the option is "Components". Bearing load inside of a hole is working okay with both options and in all directions here.

Thank you again.

[RichardOliver4462]

I am correct in saying that the bearing load still gives incorrect values? I have a model and if I apply the same load as bearing or a force I get different SPC summations?!

[John_Holtz]

Hi @RichardOliver4462

What version of In-CAD are you using? (From within the In-CAD environment, click "Nastran Support > About").

There are two different issues discussed in this thread, so it depends on which scenario you are using:

1. The magnitude of the bearing load applied to the inside of a hole was inaccurate. This was most easily seen in the support reactions (SPC Summation). From what I can see, this is fixed in versions 2018.0.2, 2018.2.1, and 2019.0. (I see there is an article on the Autodesk Knowledge Network which has not been updated to indicate that it is fixed. I will revise that article.)
2. The bearing load applied to the outside of a shaft could be in the wrong direction when the load is "Normal to Surface". This was most easily seen by the model displacing in the wrong direction. This fix is scheduled to be released soon (pending final testing, of course)

[RichardOliver4462]

Hi John,

It might have been my mistake.... but, if you select bearing force and instead of Components use Normal to Surface (which was the default on the model I was using) for the Direction, even though the force is then applied according to one Vector Fy for example the SPC summation is not the same as the applied load.

I don't think the Normal to Surface option should be available for a bearing load....

[John_Holtz]

Hi Richard,

I am seeing a small difference between using "Components" versus "Normal to Surface", but it is not to the level in my test model where I would say that one is right and the other is wrong.

Bearing load Components

Bearing load Normal to Surface

How different are your results? What version of In-CAD are you using?

I suspect that a finer mesh would produce more accurate reaction forces in my test model.

[RichardOliver4462]

I was getting an 11% difference, after a bit of mesh refinement it is down to 2% difference. I would expect though that the SPC Summation would always give the same as the applied loads..... 

I'm using version 2019.1

[matthew.cookXCL5S]

Hi Guys,

Hoping I don't need to ask, but, was this ever fixed completely? Designing a chain hook for a 300 ton ROM hopper right now and I would certainly like to know.

Edit: I suppose I could test it, but still would be nice for this to be closed out.

Cheers

[bmcwilliam]

Also looking for an update, are bearing loads in Nastran In-Cad functioning correctly now? Or are there still inconsistencies in certain scenarios? 

If resolved, from which Inventor version onwards was it fixed?

[John_Holtz]

Hi everyone,

This article applies to Inventor Nastran versions 2019 and onward: Bearing load applied normal to surface affected by mesh size in Inventor Nastran (autodesk.com)

In summary, applying the bearing load using "Components" produces the most accurate reaction force. Using "Normal to surface" is not as accurate.

John