Yade

Rolling, static and kinetic friction in Yade

Asked by Alexander

Hello everybody.

I'm a little bit confused with types of frictional contact in Yade. Lets consider CohFrictPhys class and 3 types of friction rolling, static and kinetic.

In the documentation there are only static and kinetic friction well described (I mean shear force computation for them), so where is rolling friction coefficient and how shear force depends on it?

Also lets consider simple example: One sphere lies motionless on the plane which is parallel to the ground (no cohesion links). Then we start to pull it with the force parallel to the plane. So how Yade chooses what this sphere should do (roll or slide) on the plane when maximum shear force is reached? (i mean the end of static friction).

with regards Alexander

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Alexander (karavaev-alexander) said : 		#1

Hm, may be sphere will begin roll and slide simultaneously?

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Bruno Chareyre (bruno-chareyre) said : 		#2

Hi Alexander,
There is no kinetic friction, there is shear, rolling and twisting.

>so where is rolling friction coefficient...
https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.CohFrictMat.etaRoll

>... and how shear force depends on it?
No dependency. Rolling friction limits the bending to etaRoll*radius*normalForce.

>So how Yade chooses what this sphere should do (roll or slide)

It deends which threshold (friction vs. etaRoll) is reached first.

Bruno

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Alexander (karavaev-alexander) said : 		#3

Hi Bruno, thank u for response.

Am i right that:

1) The limit for twisting is etaTwist*radius*normalForce?

2) The twisting doesn't depend on shear and rolling and may start to work independently (there is now "friction vs. etaTwist" or "etaRollvs. etaTwist")?

3) Also, does computation of rolling and twisting components depend on CohFrictPhys::cohesionDisablesFriction = True (False)

with regards, Alexander

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Alexander (karavaev-alexander) said : 		#4

And the last one today:)

If etaTwist < 0 or etaRoll < 0, it means there is no "twisting" or "rolling" friction?

with regards, Alexander

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Launchpad Janitor (janitor) said : 		#5

This question was expired because it remained in the 'Open' state without activity for the last 15 days.