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Amethyst

## Problem in specifying rotation constrainsts

Actually, i am working on a differential which getting some forces from pinion.

These forces would make an impact on the body to rotate bolt in x-direction.

So, i want to hold the bolt in x-direction of rotation to see the effects of forces.

But as i am doing this i am geeting a warning that these constrainsts wont make any effect.

Ihow should i move forward to analyse the case correctly

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## Re: Problem in specifying rotation constrainsts

Yes a cylindrical csy (created in simulate mode) is a way to do this.  Always attempt a Free Body Diagram.  You seem to be missing the loads/constraints at the output shafts. (R in my image).

Also, the pinion load may be statically redundant if using 2 pinion gears as is typical.  The load may be higher on one pinion gear than another based on manufacturing tolerances and wear.  I would not assume full halving of stress and load is happening due to the 2nd pinion gear.

Also see this for my quiz on mechanizing a differential.

FEA RING GEAR

21 REPLIES 21
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## Re: Problem in specifying rotation constrainsts

A basic, fundamental fact of 3D solid elements is that they do not/cannot possess DOF in rotational directions. I will assume you are modeling the areas you wish to apply rotational DOFs with solid elements. If so, Simulate will not allow this type of constraint. Some codes allow for "tricks" through clever interface coding to allow some application of rotational BCs - and these are usually limited, like the "TLAP" in Simulate.

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## Re: Problem in specifying rotation constrainsts

What should I do in such case if I want to restrict the rotation?

If it was not possible, then it would have been shown greyed. But at this point, i can apply it but it's not making an effect.

Am I doing something wrong while defining other parameters or its just not possible?

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## Re: Problem in specifying rotation constrainsts

Can you use a pin/cylindrical joint constraint? This should allow you to trap the desired direction.

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## Re: Problem in specifying rotation constrainsts

The rotation of the pin joint can be allowed or suppressed about the axis of the cylinder surface.

In this case in the x-direction.

But here I want it to restrict rotation in the Y direction to solve the purpose.

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## Re: Problem in specifying rotation constrainsts

Yes a cylindrical csy (created in simulate mode) is a way to do this.  Always attempt a Free Body Diagram.  You seem to be missing the loads/constraints at the output shafts. (R in my image).

Also, the pinion load may be statically redundant if using 2 pinion gears as is typical.  The load may be higher on one pinion gear than another based on manufacturing tolerances and wear.  I would not assume full halving of stress and load is happening due to the 2nd pinion gear.

Also see this for my quiz on mechanizing a differential.

FEA RING GEAR

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## Re: Problem in specifying rotation constrainsts

Even after using the cylindrical co ordinates. it is showing same Warning box after applying rotational constraints

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## Re: Problem in specifying rotation constrainsts

You can't fix the rotation of a surface in that manner.

If you want to fix the rotation and you are not interested of surface deformation, then you might use the pin constraint. Otherwise you should put a point in the centre of the hole, then use a weighted link and then put a ground spring on the point with a very high values of all stiffness.

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## Re: Problem in specifying rotation constrainsts

i would try that fraulini

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## Re: Problem in specifying rotation constrainsts

When using cylindrical CSY, Theta is the rotation.

Degree of freedom 1 is R (radial), DOF 2 is Theta (rotation about Z) and DOF 3 is Z translation.

Leave those other rotations free. (DOF 4,5,6)

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## Re: Problem in specifying rotation constrainsts

Hey SweetPeasHub,

i have tried the same constrainst and its running good at linear analysis. But its taking like 3 days for non linear analysis and still it is not completed.

I have given contacts between different components with finite co-effcient of friction.

What do you suggest in this situation?

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## Re: Problem in specifying rotation constrainsts

Contacts can be very difficult and take several tries.  There are many related articles in the community.

1. Do not have Creo automatically find contact pairs.  Manually pair all combinations.

2. Do not expect large sliding distances to work very well.  Even a single plastic clip engaging or disengaging can be difficult.

3. Start with defining the most simple contacts first.  Reduce/Limit the number of contacts. (# reported in the run information)

4. Check constraints.  Sometimes adding some spring idealizations can add force feedback to stabilize a model constrained by friction.

5. Element sizes are much more important at the contact locations.

6. Try some small initial part inter-penetration at the start.

7. Set the number of steps higher (for example user defined steps 81, space equally)

8. When too much is going on in terms of contacts I resort to other software using H-element codes like Nastran/Optistruct. (Many others)

Can you share your model so we can take a closer look?  (Use Choose Files button).

Please, for images in your post, do not cut and paste, nor use the choose files button, instead use the Photos button in the toolbar above your post to load them right into your post text.

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## Re: Problem in specifying rotation constrainsts

Here are the files and assembly of the following...

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## Re: Problem in specifying rotation constrainsts

You have to zip the file(s) before attaching.

Select all the files, Right Click, Send to , Compressed (zipped) folder.

Then attach the .zip.

Include the .asm and .prt files needed.

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## Re: Problem in specifying rotation constrainsts

yes, I have zipped them before attaching... You can have a look now

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## Re: Problem in specifying rotation constrainsts

My take on this model is attached.

Analysis1 has bolt preload but no finite friction on the contacts (CREO limitation) To run this you need to turn friction to none on the four contact interfaces (Interface2,4,5,6)
Analysis2 does not have bolt preload but has finite friction. The interface frictions might need to be turned back on. I used a Creo parameter named MU_STATIC to control the friction from a parameter. Instead of typing 0.2, type MU_STATIC. To change the value use TOOLS - PARAMETERS.

Some parts were de-featured and element size increased to reduce element count (to about 50k elements)
Volume regions were used to separate key contact areas better and to reduce contact searches.
Bolt preload was modeled as volume prismatic preload using the portion of the bolt within the clearance hole.
Some light springs were added to prevent unconstrained parts. (roll pin and pinion bolt)
The 3 gear loads were merged into one load defined by three components. Also surface regions were added to the gear to spread the load over portions of 3 gear teeth.
The ring gear was made a free interface to the housing and then a contact interface defined at the bolt face to absorb the bolt preload.
I think the axial force that opposes the helix angle will be taken by the end of the housing not the pinion bolt so I only held the pinion bolt in Theta. (The light spring was used to stop any small movement)
Your solver memory was set to 512MB. This should be about 1/2 machine ram up to 16384MB.
I used 4000MB.  Analysis1 took about 40 minutes.  Analysis2 has not finished yet.

Analysis1 Result

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## Re: Problem in specifying rotation constrainsts

Hello SweetPeasHub,

I really appreciate your efforts and I don't know how to thank you for your efforts.

I had a question like in which version have you solved this analysis. Because i am having creo 4.0 and it is showing as invalid file

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## Re: Problem in specifying rotation constrainsts

Hi,

You wrote:

"... Analysis2 ... has finite friction. ... Analysis2 has not finished yet. ..."

finite friction doesn't good work

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## Re: Problem in specifying rotation constrainsts

Yes, finite friction does not work well.  However this worked.  It took about 2 hours to run.

Analysis2 Results

Note  that results are very similar to Analysis1, however the contact pressure shows how we are missing the contact pressure due to bolt preload.  My opinion is that the finite friction is not needed.  I might compare friction None to friction Infinite but doubt that makes much difference either.

The shear stress at the pin is about 130MPa by hand calculation.  The model has the pinions further from the housing than reality so bending stress is artificially introduced to the pin.  This is to keep St Venant's principal working as we get to the housing by having the constraint further away.  For more correct stress on the pin, the pinion gears would need to be included, with contacts to the pin, or the constraint must be replaced by a bearing load and then constraining at the gear tooth instead of loading.  Or a third option is to have full free body loads and applying inertia relief constraint.

Sorry about using Creo5.  When I get time I will try to demonstrate how this was done so it can be replicated in Creo4.

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## Re: Problem in specifying rotation constrainsts

Hey SweetPeasHub,

This explanation isn't helping perfectly. as I have tried doing it but still landing on some errors with contact and constraints.

Is there any way to convert your files and open in Creo 4.0

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## Re: Problem in specifying rotation constrainsts

I don't know of a way to convert from Creo 5 to Creo 4.  Also there are just so many steps taken to describe.  I can give images... sorry too many words to explain.  I will let you ask the questions where it is unclear.

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