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# Small Sliding

Hello,

I have a question regarding contacts in Sol 101.

My collegues showed me that in Abaqus there is the possibility to apply a contact called small sliding contact.

The second possibility is finite sliding contact which is in my opinion comparable to the surface to surface contact of NX in Sol101.

My question now is, is in NX also something like the small sliding contact of Abaqus available?

Thank you.

Regards,

Georg

6 REPLIES
Solution
Solution
Accepted by topic author GStrickner
‎08-26-2015 04:32 AM

## Re: Small Sliding

[ Edited ]

Dear George,

If the problem is linear (ie, if the geometric nonlinearities present in the FE can be neglected and both contact surfaces are touching physically, ie, initial gap zero), then I am sure the contact Stress solution obtained by both NX NASTRAN SOL101 & Abaqus will be similar. But if you have large displacements effect (or not small displacements) then the linear surface-to-surface contact is useless, you need to run the Advanced Nonlinear Solver SOL601,101 with genuine nonlinear contact.

In Linear Contact (SOL101) the software assumes that penetration of the hitting point occurs along the direction of the hitting face normal. Therefore, wedge-type problems with finite sliding may be poorly simulated using linear contact analysis because contact elements are created only once using the initial geometry of the problem.

Also in Linear Contact (SOL101) when two surfaces are separated by an initial gap and the direction of motion is significantly different than the surface normal, then significant errors may occur (for example, wrong location for target face stresses). If the initial gap is zero (or very small), the error may be negligible.

In Advanced Nonlinear (SOL601) you have features like "Small Displacement Contact": the contact constraints are generated once in the beginning of the analysis and are kept constant. This feature is useful when there is very little relative deformation around the contact region. For such problems, it is much more computationally efficient to perform only one detailed contact search at the beginning of the analysis, rather than repeating the search every iteration. Also, in some cases, convergence can also be slow or unachievable with the general algorithm, for example as nodes oscillate between one target segment and another equally valid neighboring target segment.

Surface-to-Surface Contact in Advanced Nonlinear (SOL601) is really powerful, here you are an overview:

• The points of contact are assumed not known a priori.
• Friction can be modeled according to various friction laws (only standard Coulomb friction for Solution 701).
• Both sticking and sliding can be modeled.
• Repeated contact and separation between multiple bodies is permitted in any sequence.
• Self-contact and double-sided contact are permitted.
• Tied contact can be modeled (Solution 601 only).
• A small displacement contact feature is available.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

## Re: Small Sliding

Hello Blas,

thank you for your detailed answer.
I raised this question because I need to consider two bearing rings in my model. Usually I would glue them, but in this special case I need to keep the relative rotation to each other free, so that I can transmit a rotational moment from on ring over a console to the frame on which the second ring is mounted. Therefore I am using the usual surface-to-surface contact as available in Sol101.
Unfortunately this contact slows down my calculation a lot because it is used in several subcases.

Is there any other option to keep the rotational movement free between the two rings?

Regards,

Georg
Solution
Solution
Accepted by Ganesh_S (Community Manager)
‎08-26-2015 04:32 AM

## Re: Small Sliding

Dear Georg,

Yes, and is very easy & practical, no need to enter in the world of surface-to-surface contacts unless you need to know locally the contact stress: the key is to use CBUSH elements!!.

For instance, to set up an example, in the image below the link arm is modeled using 1-D CBEAM elements. The link rotates freely around the axis of bracket holes meshed with 3-D Solid CHEXA elements, then to achieve this movement a CBUSH node-to-node elements was used between the node of the CBEAM element and the INDEPENDENT core node of RBE2 spider-like element in the center of the bracket hole.

In the properties of the CBUSH element simply enter a big value (say 1E6) for the translational stiffness and let zero the rotational DOF stiffnes, this way you define a local pin joint.

To check that everything runs as expected, simply I let the end of the link free and run a Modal vibration analysis: the 1st mode should be the zero rigid-body mode shape with the rotation of the link around the bracket hole!.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

## Re: Small Sliding

Blas,

thanks a lot for your fast answer and the hint. I will try your solution. I guess it will work.

Thank you.

Georg

## Re: Small Sliding

CBUSH is not the only option on this. CBAR/CBEAM can be used in the same manner with end releases. RBAR/RBE2 can also be used with Pin Flags.

## Re: Small Sliding

And definitely more elegant, and looks better in presentations too