[lammps-users] Void growth simulation

Hello everybody,

I am a beginner in LAMMPS and am trying to modify the shear.void example of LAMMPS both to learn LAMMPS and to study the effects of different parameters on the void growth mechanism. I have modified the input file such that the voided body is not under shear anymore and experiences tension. I have a few questions in this regard:

  1. How can I get the tensile force induced by the applied velocity? I tried the “fix setforce” command for the upper boundary and lower boundary but it always generates zero force.

  2. Why does the failure always take place at the place where the voided body is connected to the upper boundary? This is clearer when the void size is rather small.

  3. I modified the ramp velocity command for the tension problem. Does it look OK?



Here is the modified script for your information:

3d metal shear simulation

units metal

boundary s s p

atom_style atomic

lattice fcc 3.52

region box block 0 30.0 0 30.0 0 2.828427

create_box 3 box

lattice fcc 3.52 orient x 1 0 0 orient y 0 1 1 orient z 0 -1 1 &

origin 0.5 0 0

create_atoms 1 box

pair_style eam

pair_coeff * * Ni_u3.eam

neighbor 0.3 bin

neigh_modify delay 5

region lower block INF INF INF 0.9 INF INF

region upper block INF INF 20.1 INF INF INF

group lower region lower

group upper region upper

group boundary union lower upper

group mobile subtract all boundary

set group lower type 2

set group upper type 3


region void cylinder z 15 10 4 INF INF

delete_atoms region void

temp controllers

compute new3d mobile temp

compute new2d mobile temp/partial 0 1 1


velocity mobile create 300.0 5812775 temp new3d

fix 1 all nve

fix 2 boundary setforce 0.0 0.0 0.0

fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0

fix_modify 3 temp new3d

thermo 25

thermo_modify temp new3d

timestep 0.001

run 100


velocity upper set 0 1.0 0

velocity mobile ramp vy 0 1.0 y 0.9 20.0 sum yes

unfix 3

fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0

fix_modify 3 temp new2d

dump 1 all atom 100 dump.shear

thermo 100

thermo_modify temp new2d

reset_timestep 0

run 3000

You can apply tension by pulling on boundaries (set initial velocity,
turn off force, integrate), or using fix deform.