create an initial crack

Hello all.

i want to create an edge and a center crack in boron-nitride sheets. i just want to know that what is the best way for creating this crack?

should i delete few rows atoms by delete-atoms comment to create crack? or there is a better way to do that?

I already defined some block region and create crack by delete-atoms comment but the crack tip is not enough sharp as i want. See the comments below:

Region 1 (Left side)

region leftSide block 0 247.2 INF INF INF INF units box

group leftSide region leftSide

Region 2 (right side)

region rightSide block 252.8 500 INF INF INF INF units box

group rightSide region rightSide

Region 3 (lower side)

region lowerSide block INF INF 0 220 INF INF units box

group lowerSide region lowerSide

Region 4 (upper side)

region upperSide block INF INF 280.5 500 INF INF units box

group upperSide region upperSide

group center-crack subtract all leftSide rightSide lowerSide upperSide

There is any better way that i can use?

Thank you so much in advance and i really appreciate for your help.

With the best regards,

Rouzbeh

Hello all.

i want to create an edge and a center crack in boron-nitride sheets. i just want to know that what is the best way for creating this crack?

should i delete few rows atoms by delete-atoms comment to create crack? or there is a better way to do that?

I already defined some block region and create crack by delete-atoms comment but the crack tip is not enough sharp as i want. See the comments below:

Region 1 (Left side)

region leftSide block 0 247.2 INF INF INF INF units box

group leftSide region leftSide

Region 2 (right side)

region rightSide block 252.8 500 INF INF INF INF units box

group rightSide region rightSide

Region 3 (lower side)

region lowerSide block INF INF 0 220 INF INF units box

group lowerSide region lowerSide

Region 4 (upper side)

region upperSide block INF INF 280.5 500 INF INF units box

group upperSide region upperSide

group center-crack subtract all leftSide rightSide lowerSide upperSide

There is any better way that i can use?

Thank you so much in advance and i really appreciate for your help.

With the best regards,

Rouzbeh

Thank you so much dear Ray,
I’ve already seen the example, but as I’m not pro in lammps, I just understood that a few region is defined, but I could’nt fine which comments have been used to create the crack. Could you guide me about that? I really appreciate for your help
This is the input that you mentioned:

dimension 2
boundary s s p

atom_style atomic
neighbor 0.3 bin
neigh_modify delay 5

# create geometry

lattice hex 0.93
region box block 0 100 0 40 -0.25 0.25
create_box 5 box
create_atoms 1 box

mass 1 1.0
mass 2 1.0
mass 3 1.0
mass 4 1.0
mass 5 1.0

# LJ potentials

pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 2.5

# define groups

region 1 block INF INF INF 1.25 INF INF
group lower region 1
region 2 block INF INF 38.75 INF INF INF
group upper region 2
group boundary union lower upper
group mobile subtract all boundary

region leftupper block INF 20 20 INF INF INF
region leftlower block INF 20 INF 20 INF INF
group leftupper region leftupper
group leftlower region leftlower

set group leftupper type 2
set group leftlower type 3
set group lower type 4
set group upper type 5

# initial velocities

compute new mobile temp
velocity mobile create 0.01 887723 temp new
velocity upper set 0.0 0.3 0.0
velocity mobile ramp vy 0.0 0.3 y 1.25 38.75 sum yes

# fixes

fix 1 all nve
fix 2 boundary setforce NULL 0.0 0.0

# run

timestep 0.003
thermo 200
thermo_modify temp new

neigh_modify exclude type 2 3

#dump 1 all atom 500 dump.crack

#dump 2 all image 250 image.*.jpg type type &
# zoom 1.6 adiam 1.5
#dump_modify 2 pad 4

#dump 3 all movie 250 movie.mpg type type &
# zoom 1.6 adiam 1.5
#dump_modify 3 pad 4

run 5000

Quoting Ray Shan <[email protected]>:

Thank you so much dear Ray,
I’ve already seen the example, but as I’m not pro in lammps, I just
understood that a few region is defined, but I could’nt fine which
comments have been used to create the crack. Could you guide me about
that? I really appreciate for your help
This is the input that you mentioned:

dimension 2
boundary s s p

atom_style atomic
neighbor 0.3 bin
neigh_modify delay 5

# create geometry

lattice hex 0.93
region box block 0 100 0 40 -0.25 0.25
create_box 5 box
create_atoms 1 box

mass 1 1.0
mass 2 1.0
mass 3 1.0
mass 4 1.0
mass 5 1.0

# LJ potentials

pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 2.5

# define groups

region 1 block INF INF INF 1.25 INF INF
group lower region 1
region 2 block INF INF 38.75 INF INF INF
group upper region 2
group boundary union lower upper
group mobile subtract all boundary

region leftupper block INF 20 20 INF INF INF
region leftlower block INF 20 INF 20 INF INF
group leftupper region leftupper
group leftlower region leftlower

set group leftupper type 2
set group leftlower type 3
set group lower type 4
set group upper type 5

# initial velocities

compute new mobile temp
velocity mobile create 0.01 887723 temp new
velocity upper set 0.0 0.3 0.0
velocity mobile ramp vy 0.0 0.3 y 1.25 38.75 sum yes

# fixes

fix 1 all nve
fix 2 boundary setforce NULL 0.0 0.0

# run

timestep 0.003
thermo 200
thermo_modify temp new

neigh_modify exclude type 2 3

It is this command here by excluding type 3 atoms from the neighbor lists of type 2 atoms and vice versa, it effectively creates a “crack” where these two types of atoms don’t see each other. Note several lines above the set commands were used to change atom types for groups leftupper and leftlower.

Ray