Crack initiation in molecular dynamics

 In this blog, I will be showing how to initiate a crack in the molecular dynamics method. For this, I am using aluminium as an example.

Input script

####distance-amstrongs,mass-gram/mole

units metal 

boundary s s p 

atom_style atomic 

neighbor        0.3 bin

neigh_modify    delay 5

####to print values from thermo command

log logfile.txt 

####dimensions of simulation box-this dimension should generate 48000 Al atoms

region          1 block 0 159.44 0 119.58 0 39.86 units box 

create_box      5 1

####filling atoms inside the simulation

lattice         fcc 3.986

create_atoms    1 region 1 basis 1 1 basis 2 1 basis 3 1 basis 4 1 units box

####this should create 5 regions and 5 groupes

region          2 block 0 51.818 59.79 111.608 0 39.86 units box

group           leftupper region 2

region          3 block 0 51.818 7.972 59.79 0 39.86 units box

group           leftlower region 3

region          4 block 0 159.44 0 7.92 0 39.86 units box

group           lower region 4

region          5 block 0 159.44 111.608 119.58 0 39.86 units box

group           upper region 5

####this should assign 5 atom types to 5 groups

set             group leftupper type 2

set             group leftlower type 3

set             group lower type 4

set             group upper type 5

####mass of Al atom is 26.982 gram/mole. * indicates all atom types ie. 1 and 2

mass            * 26.982

pair_style eam

pair_coeff * * Al_jnp.eam

####energy minimization

minimize        1e-7 1e-9 10000 10000

timestep        0.001

####crack formation

group           boundary union upper lower 

group           mobile subtract all boundary

velocity        mobile create 298 887723 dist gaussian mom yes rot yes

velocity        upper set 0.0 0.3 0.0

velocity        mobile ramp vy 0.0 0.3 y 7.04 98.56 sum yes 

fix             1 all nve 

fix             2 boundary setforce NULL 0.0 0.0

neigh_modify    exclude type 2 3

dump dump_1     all custom 500 dump.min id type x y z ix iy iz vx vy vz

thermo          500 

thermo_style    custom step time temp pe etotal press vol

run             40000

unfix           1

unfix           2

undump          dump_1

####end

Visit LAMMPS Manual page for detailed explanation of commands used.

Potential file used here can be found in LAMMPS directory of your computer.

Simulation

Explanation

1. Bottom region of the simulation box was fixed and a small velocity was applied to the top region. Hence a crack was initiated and propagated. 

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