Contact constants

Submitted by CARLOS AVILA on Wed, 10/06/2010 - 05:46

I am using Hertz contact in LAMMPS. Would some body please let me know a set of equations that I can use to compute normal and tangential stiffness, normal and tangential dumping coefficients from material constants like E, G, mu. Thank you in advance

Forums:

ckloss's picture

ckloss | Wed, 10/06/2010 - 08:10

Hi Carlos,

this is readily implemented in LIGGGHTS. Please see the LIGGGHTS doc of pair/gran that comes with the LIGGGHTS tarball - or search "discrete element contact law" on sciencedirect for papers.

Christoph

CARLOS AVILA | Wed, 10/06/2010 - 18:03

Hi Christoph,
Thank you so much for your reply.
I've been using the equations proposed in the manual for Kn and Kt. My question araises since I am trying to calibrate the parameter of my infinite slope model. In order to do so, I am running a very simple simulation where I drop only one(1) particle inside of a simulation box.
What I am observing is rare since the particle bounce back to its original position or even slightly higher as many times as it is allow by the time domain that I set in the input file.
It seems obvious to me that the damping factors that I am using are incorrect and I've been playing with very different values for gamma-n and gamma-t.
I've not been able to find in the manual equations for gamma(damping factor) and that was the reason of my question. Any thoughts about my problem. THank you so much in advance.
Regards,
Carlos

ckloss's picture

ckloss | Wed, 10/06/2010 - 19:18

Hi Carlos,

are you sure you are using LIGGGHTS, not LAMMPS? in LIGGGHTS, not the damping values gamman, gammat are specified, but the coefficient of restitution (COR) - gamman, gammat are calculated so that the COR provided by the user is reached - the formula is given in the doc of pair_gran

>>What I am observing is rare since the particle bounce back to its original position
This is governed by the COR - have a look in part 1 of the LIGGGHTS course documents - you will find the relationship there

Cheers,
Christoph