Dear LAMMPS users,

I compared the Hertzian style formula in the documentaion (http://lammps.sandia.gov/doc/pair_gran.html):

Fn = 4 * G / (3 * (1 - nu)) * sqrt(R/2) * delta^(3/2)

with the formula in the Zhang paper:

Fn = 8 * G / (3 * (1 - nu)) * sqrt(R) * delta^(3/2).

If I'm doing the algebra correctly, the forces differ by a factor of 2^(3/2)?

With kind regards,

Thomas Wagner.

Jeremy - do you want to comment on this?

Steve

All,

I think I made this mistake myself before. I believe the lammps

documentation is correct; assuming that the grains have identical

properties (i.e., Shear Modulus and Poisson Ratio). You will notice the

the extra factor of 2^(3/2) appears in the Zhang and Makse paper in

their definition of the "normal overlap" just following equation 1. Can

someone verify?

In addition, the equation in the lammps documentation does match the

standard result from Hertz theory (see e.g., K. L. Johnson, "Contact

Mechanics", Cambridge University Press, pp 90-93.); again, assuming

identical materials properties.

Jeremy