[lammps-users] Stress Fluctuations in Granular System

Dear LAMMPS Users,
I simulated a granular system (about 4000 particles in a cubical box, with gravity downwards direction and application of shear on the walls). When i plotted the shear stress on the wall (the plot is attached) i see that the stress fluctuations dies off after some initial time steps and stress profile becomes very smooth. I am calculating the stress on the wall as = Force on the wall / Wall area.

Is this the right behavior of the stress with time in the granular systems? My feeling is that the stress should keep fluctuating as the shear force will keep changing the configuration of granular (or co-ordination number) particles. I am not very sure about this behavior of stress evolution, can anybody please help me in understanding it or share his/her experience.


Shear Stress vs Time.jpg

Granular systems are damped, so over time things tend to settle
and stresses die out. Unless you are driving the system in some
other manner (shaking, flowing, etc), then what you see is typical.


Hi Steve,
Thanks for the reply, as i mentioned earlier I am applying continuous shear (by moving the walls) to the system, does it not count towards driving the system?


I didn't see that - yes, if you are shearing you are putting
energy into the system. You might be losing stress fluctuations on
the walls if the granular particles are ordering next to the
wall. Viz might help with that.