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Difference between the internal friction angle of material and the interparticle friction angle?

Asked by Chien-Cheng Hung

Hi all,

According to the comments in [1], Luc mentioned not to mix up the internal friction angle of a material and the interparticle friction angle.

I was wondering what the differences are between these two parameters.
Looking forward to getting your answer.

[1] https://answers.launchpad.net/yade/+question/678523

Cheers,
Chien-Cheng

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Jérôme Duriez
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Jan Stránský (honzik) said : 		#1

Hello,

please provide more information [2].

What is "internal friction angle of material"? Yade material value? Yade overall macroscopic value? Parameter of a real material? ... ?

What is "interparticle friction angle"? Some Yade value? Or a value of real particles? Or ... ?

Cheers
Jan

[2] https://www.yade-dem.org/wiki/Howtoask

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Chien-Cheng Hung (chiencheng) said : 		#2

Hi Jan,

Sorry, let me make it clear.

As far as I know, the friction angle we assign or modify in [1] and [2] stands for the internal friction angle of the material.
In the meanwhile, these two parameters also represent the interparticle friction angle that describes the contact friction between particles.

I happened to see Luc's comment in [3] saying not to mix up the internal friction angle of material and the interparticle friction angle which I think are the same thing based on my understanding.

So I would like to ask whether the values in [1] and [2] can also be considered as the interparticle friction coefficient?

Cheers,
Chien-Cheng

[1] https://yade-dem.org/doc/yade.wrapper.html?highlight=frictionangle#yade.wrapper.FrictMat.frictionAngle
[2] https://yade-dem.org/doc/yade.utils.html?highlight=setcontactfriction#yade._utils.setContactFriction
[3] https://answers.launchpad.net/yade/+question/678523

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Best Jérôme Duriez (jduriez) said : 		#3

Above [1] and [2] point to a contact property between 2 Discrete Elements, that's it.

If you take any DEM paper from the literature with some macro-scale shear strength considerations (e.g. triaxial testing), and compare the deduced material friction angle (e.g. Mohr-Coulomb criterion friction angle) with that contact property you will see how different both can be (except in few instances where you would be very lucky -- or unlucky -- and get an equality between the two).

See e.g. https://www.sciencedirect.com/science/article/pii/S0266352X21005309 where Mohr Coulomb friction angle is above 35 degrees, vs a contact friction angle at 31° for a polyhedron model ("Set 2 parameters" in Table 5).

Most convincing example would certainly be your own YADE simulations of triaxial tests, with zero FrictMat.frictionAngle.

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Chien-Cheng Hung (chiencheng) said : 		#4

Thanks Jérôme Duriez, that solved my question.