# Friction less Contact 3-Point Bending

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• Last Post 06 October 2018
learn13 posted this 05 October 2018

I'm attempting to create something similar to a standard 3 point bending simulation in static structural but the default bonding definitions between the primary geometry and 'pins' pose an obvious problem.  I've attempted using the friction less contact definition with additional changes to the, connections Pinball Region, Detection Method, and substeps.  But have been unsuccessful so far.

Any tips or tutorials would be greatly appreciated.

I would prefer to use Static Structural over Explicit for this application.

peteroznewman posted this 05 October 2018
akhemka posted this 05 October 2018

Just a comment - one may try this on a 2D model as well.

learn13 posted this 05 October 2018

Thank you for your replies.  I'm working within workbench, both 2D and 3D models have been attempted (thank you @akhemka).  But the issue is defining a frictionless contact definition between the pins and primary geometry.  @peteroznewman, I learned several good points from your post that will be applicable in future projects, but I'm not sure it will represent the current problem.

The pins are placed on the top and bottom faces of a 'plate', as in a standard 3 point bending test.  I will not be fixing the outer edges of the plate.  I've also attempted splitting edges/faces for 2D or 3D cases but did not receive a satisfactory results.  The plate does not rotate/slide over the pins as it would in experimental conditions shown in the photo below. (sliding may be more in the realm of explicit).

http://www.substech.com/dokuwiki/lib/exe/fetch.php?w=&h=&cache=cache&media=3-point_flexure.png

peteroznewman posted this 05 October 2018

Is your specimen symmetric about the breadth dimension (along the loading pin length)? If so you can use Symmetry and cut the model in half again and have a quarter model.  That means when you apply the force to the cut center edge, you only apply 1/4 of the total force and don't need to model the roller.

Once you have done that, you can slice your model at the support roller and use a displacement support on the newly created edge. With just the vertical axis set to zero, that support acts like a frictionless roller, without having to model the roller.

Regards,
Peter

learn13 posted this 06 October 2018

These are great considerations.

However, if I wanted to create a model with the plate and pin, how would I create a appropriately defined frictionless contact definition?

Several different modifications to the connection definitions (frictionless), fixed face definitions (frictionless support with bonded or frictionless connections), and (as you have suggested) using an edge as a means of disallowing only vertical displacement.  The edges were in the place of the pins and modeled by splitting the bottom face in those positions.

The frictionless contact I'm trying to emulate is demonstrated within the tutorial below (skip to 14:18).  However, my pins and plate will not be made of shell elements.

Best,

Lrn13

peteroznewman posted this 06 October 2018

You can use solid elements for the beam and the support and loading rollers.

If you have symmetry, you can still use a 1/4 model.

If you have a 1/4 model then you can use frictionless contact between the rollers and beam.  If you go with a full model, you want at least one contact to be frictional, otherwise, the beam will slip away from the rollers.

You can have fixed support on the support roller(s). For the loading roller, create a Translational Joint to ground and use a Joint Load to apply either a force or the preferred choice, a displacement.

Here is another Discussion you can review.

Regards,
Peter