I am trying to use peridynamics in lammps. I tried to simulate tensile test on a 3D bar based with similar material mentioned in lammps-peridynamics tutorial (K = 14:9 GPa). The stress-strain response is supposed to give reasonable value of “E”. But once I apply velocity boundary condition at the top of the bar its not giving any displacement in the system. I’m sure there is some mistake in the input file.
I’ll really appreciate if I can get some hint about what’s going wrong in my input file.
Thanks in advance
Best regards
Rezwan
Input file:
units si
boundary s s s
atom_style peri
atom_modify map array
neighbor 0.0010 bin
lattice sc 0.001
region bar block 0.0 0.01 0.0 0.05 0.0 0.01 units box
create_box 1 bar
create_atoms 1 region bar
Yes, I tried to analyze the velocity and force on atoms printed in dump file using the following command:
dump 1 all custom 1000 atomPERi.lammpstrj.* id type xs ys zs ix iy iz vx vy vz fx fy fz
Velocity of order 10e-6 was assigned at the initial step (observed from dump file) whereas in the input file I assigned Vy=0.001 m/s. I also observed that the velocities and forces are nonzero on some sets of atoms throughout the system. Moreover, I printed “Ly” which remains unchanged throughout the simulation. As the velocity BC is applied along Y-axis, shouldn’t “ly” be changing?
Hi,
I also have problems with the peridynamics package and I haven’t figure out how to deal with them yet. My problems are when I restart a simulation and with the addforce command. When I add a force to a particle after restart the components do not add properly. I also try to use the neigh_modify command to make an initial crack but it doesn’t seem to work. Damage is not calculated. One more thing, the restart2data tool doesn’t work with the pair/pmb. Please let me know if somebody could advise on these problems.
Best,
Harry.
Forces between particles in a PD model are not
simply pairwise neighbor forces. There are also bonds.
Setting neigh exclude does not change the bonds, which
in fact dominate.
timestep 1e-7
set group all density 2200
set group all volume 1.25e-10
region top block INF INF 0.485 INF INF INF units box
region bottom block INF INF INF 0.015 INF INF units box
group topface region top
group bottomface region bottom
group boundary union bottomface topface
group mobile subtract all boundary
compute new mobile temp
velocity mobile create 0.01 887723 temp new
velocity topface set 0.0 0.1 0.0 units box
velocity mobile ramp vy 0.0 0.1 y 0.015 0.485 sum yes units box
variable R equal 40000
fix ENG all nve
fix 2 boundary setforce NULL 0.0 NULL
thermo_style custom step temp etotal press ly
thermo 100
thermo_modify flush yes
dump 1 all custom 10000 atomPERi.lammpstrj.* id type xs ys zs ix iy iz vx vy vz fx fy fz
run $R
I put these lines in your script and looked at the 2 output files on step 0
dump 1 mobile custom 10000 tmp1.* id x y z vx vy vz
dump 2 topface custom 10000 tmp2.* id x y z vx vy vz
You have these lines defined previously:
velocity mobile create 0.01 887723 temp new
velocity topface set 0.0 0.1 0.0 units box
velocity mobile ramp vy 0.0 0.1 y 0.015 0.485 sum yes units box
All is as expected. The topface atoms all have v = 0 0.1 0.0
The mobile atoms have a small thermal component superposed on
top of something that is nearly vy = 0.0 at the y-bottom of the box, and
nearly vy = 0.1 at the y-top of the box.