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:
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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.
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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.
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I modified the ramp velocity command for the tension problem. Does it look OK?
Best,
Amir
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
void
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
equilibrate
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
shear
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