How to define internal friction angle

Submitted by venes520 on Mon, 02/13/2012 - 17:18

Hi guys!

I am currently learning LIGGGHTS to simulate the Direct Shear Box Test for soil and thinking about the Granular package.
Under the pair_style gran/hertz/history/stiffness command, I am able to define the stiffnesses of soft contact and damping constants etc,
however, I also want to define the internal friction angle of particles to describe the particle-particle friction coefficient.

Anyone can help me out on that?

Forums:

cstoltz | Tue, 02/14/2012 - 12:22

There is a paper by Ketterhagen et al that provides a connection between internal friction angle and particle-particle friction coefficient based on their work and that of some others on flow from bins & hoppers. Should be a good place to start.

Ketterhagen et al, Powder Technology, 195 (2009), 1-10

Best regards,
Chris

venes520 | Wed, 02/15/2012 - 07:47

Dear Chris,

Thanks for the reply,
What confuses me is that, under the pair_style gran/hertz/history/stiffness command, I am able to define the K_n, K_t, gamma_n, gamma_t (stiffnesses and damping constants), This command uses the Hookean contact model, which is bound by an upper limit: shear force should be smaller than normal force (F_s<= coeff * F_n), 0<=coeff<=1
Therefore, we should also be able to define the upper limit, which is the coefficient of friction, or friction angle between particles.

Then I looked into the pair_style gran/hertz/history/stiffness doc file and found that there is actually a xmu(represents the coefficient of friction) built in the C++ script.
So, I figure if I can use the similar fix command to define the value of xmu:

fix coeff_friction all property/global xmu peratomtypepair 3 0.5 0.6 0.6

Do you think liggghts can understand it and is it the right way to do it?

Thanks!
Anson Liang
lzefeng@gmail.com

Cheers
Anson Liang

venes520 | Wed, 02/15/2012 - 08:51

Yes, I know that is the limit,
However, I found nowhere to input this coefficient of friction, shouldn't the limit be defined by users ?

Cheers
Anson Liang

tdl | Fri, 02/17/2012 - 15:08

I will be soon doing a similar simulation, and I have the same perplexity. Maybe I missed something?
BTW, thank you for your effort both in writing the program and supporting users.
Best,
Alessandro