Dear all

My name is Divas and I am trying to perform a simulation regarding “quasi-static shear deformation” on a 2D system of athermal disks. I am using lammps version of July 2021.

I have a 2D triclinic system of 8192 particles with particle diameter 1.0 and 1.4, with equal mass 1.Initially the tilt has been kept as 0.0 for xy , xz and yz.

Initially I created a box and randomly generate the particles. The particles are interacting via a linear elastic spring model. I have relaxed the system by using minimization technique FIRE. After the energy minimization , the overlapping between the particles got removed. the average total force on the particle and the kinetic energy of the system are of order 1.0e-10 and 1.0e-18 respectively.

After this process , I am trying to implement “Quasistatic shear deformation” and trying to implement LEES EDWARD boundary conditions. While doing so I am trying to implement an incremental strain of 0.0001 over the boundary of the box in xy plane. Now as the system is getting deformed under shear, the boundary of the box are moving but the total velocity of the particles are not changing. The total shear stress on the system is getting reduced too. The particles should flow with the shear deformation.

I am not able to understand the reason for the same. Any help is appreciated.

I have attached the input script to apply shear deformation and the data file of the particles. I am using granular pairstyle to implement the linear elastic spring model with stiffness 1000. I am using fix_deform delta (keyword) to apply the strain increment. The area packing fraction of the system is 0.9 This is the code I am using:

units si #si units of parameters

atom_style sphere

dimension 2

boundary p p p

newton off

comm_modify vel yes

read_data data.stiffness_1000

group 1 type 1

group 2 type 2

set type 1 mass 1

set type 2 mass 1

neighbor 1.2 bin

neigh_modify delay 0 every 1 check no

comm_modify vel yes

pair_style granular

pair_coeff * * hooke 1000.0 00.0 tangential mindlin 0.0 1.0 0.0 damping mass_velocity

compute peratom all stress/atom NULL pair

compute p all reduce sum c_peratom[1] c_peratom[2] c_peratom[3] c_peratom[4]

variable area equal (102*102)

variable press equal -(c_p[1]+c_p[2])/v_area

variable sigmaxy equal -c_p[4]/v_area

variable kinetic equal ke

fix 3 all enforce2d

timestep 0.0001

variable i loop 1000

label loop

fix 1 all deform 1 xy delta 0.0001 remap v units box

thermo 1

thermo_style custom step ke v_press v_sigmaxy

dump 50 all custom 1 *.stress_strain id type diameter x y z vx vy c_peratom[1] c_peratom[2] c_peratom[3] c_peratom[4]

dump 40 all atom 100 shear_aqs.dump

dump_modify 50 sort id

run 1

undump 50

next i

jump SELF loop

regards

Divas Singh Dagur