Contact (dilation) angle between particles

Asked by Chien-Cheng Hung

Hi all,

I am simulating the direct shear of a granular assemblage with different particle size distributions (PSD) (e.g., normal distribution and power-law distribution).
I want to output the contact angle between all the particles to see the distribution of it in the entire granular packing for different PSD models.
Is there any way to do that?
Thanks in advance!

Cheers,
Chien-Cheng

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Jérôme Duriez (jduriez) said :
#1

As far as I'm concerned, I would need to know what is a contact angle between particles ?

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Chien-Cheng Hung (chiencheng) said :
#2

Hi,

The contact angle using here means dilation angle (ψ). The value of ψ=0 corresponds to the volume that preserves deformation while in shear.
Since the angle of dilation (ψ) controls the amount of plastic volumetric strain and macroscopic friction developed during plastic shearing, I would like to know how the dilation angle (or contact angle) distribute in the granular layer for different PSDs and to see its relation to the volumetric strain and macroscopic friction.
I hope this is clear for you.

Cheers,
Chien-Cheng

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Chien-Cheng Hung (chiencheng) said :
#3

Just for further clarification.

In 2D, if there are two particles of the same size in contact with each other in the horizontal direction, then the contact angle between these two particles would be 90 degrees.
Similarly, if the one is right on top of the other one, then the contact angle would be 0 degrees.
The contact angle described here is what I want to output as a distribution.
I can imagine it would be a bit tricky for a 3D simulation since there are some vector issues...

Chien-Cheng

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Jan Stránský (honzik) said :
#4

Hello,

> I hope this is clear for you.

No, sorry, the question is very (and actually more and more) confusing..

How is "contact angle using here means dilation angle (ψ)" from #2 related to "the contact angle described here" from #3?

The #3 definition is really an angle (or vector in 3D) of the interaction. You have many interactions, access to the data, you can easily do whatever with the data, e.g. output a distribution.

The #2 definition is some macroscopic dimensionless quantity which is called angle "by chance" because the value can be interpreted as an angle in a graph. (similarly to the friction angle).

AFAIK ψ is a ratio of volumetric strain and shear strain.
How would you / do you want to define it for one contact / region (to make a distribution)?

> if there are two particles of the same size ...

any difference from the case of different size?

> ... horizontal ... would be 90 degrees. ... right on top of the other one ... would be 0 degrees.

How is this clear purely geometric meaning related to dilation angle (ψ) (volumetric strain / shear strain)?

Please make clear what you want.

Cheers
Jan

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Launchpad Janitor (janitor) said :
#5

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