fixed and then dump fx fy fz

Hi LAMMPS users,
I am conducting nanomachining simulation now. I have two questions, any suggestions are highly appreciated.
I dumped the forces between tool and worpiece, and added forces on each atoms together.

  1. The forces changed a lot in the cutting process, which is not reasonable.
  2. If I fixed the tool and workpiece ( like, fix the tool to rotate, and fix the workpiece to move linearly), could I still be able to compute the forces on tool and get the forces information between the tool and workpiece? Thanks!
    Best,
    Xiangcheng

Hi LAMMPS users,
I am conducting nanomachining simulation now. I have two questions, any
suggestions are highly appreciated.
I dumped the forces between tool and worpiece, and added forces on each
atoms together.
1. The forces changed a lot in the cutting process, which is not reasonable.

which forces change where and why is it not reasonable?

2. If I fixed the tool and workpiece ( like, fix the tool to rotate, and fix
the workpiece to move linearly), could I still be able to compute the forces
on tool and get the forces information between the tool and workpiece?

in the context of LAMMPS it is ambiguous to use the term "fix". best
you describe what you intended to do and then provide the input script
as well. it is impossible to discuss based on such vague statements.
there could be anything wrong and you just didn't notice.

axel.

Thanks for your reply!
Problem description:
I want to use diamond tip to cut silicon workpiece.
Tip dimension: 10 nm radius.
Workpiece dimension: 10018720 nm
Input file attached in the end

Cutting depth: 4.3 nm

For the cutting process, the normal force( force perpendicular to workpiece) and driving force ( force along the cutting direction) would not stabilize in the process. Both of them vary greatly in the process(from 0 nN to 30,000 nN)

Input file:

3d cutting simulation

units metal
dimension 3
boundary p p p

atom_style atomic
neighbor 2.0 bin
neigh_modify every 2 delay 6 page 50000 one 2000

create diamond tool geometry

region whole block 0 1000 0 187 0 200 units box
create_box 2 whole
region tool sphere 50 187 100 50 side in
lattice diamond 3.5667
mass 1 28.085
create_atoms 1 region tool
region Siworkpiece block 0 1000 0 100 0 200 units box
lattice diamond 5.43
mass 2 12.010700
create_atoms 2 region Siworkpiece

potential

pair_style tersoff

pair_coeff * * SiC.tersoff C Si

define groups

region left_fix block 0 10 0 100 0 200 units box
region left_thermo block 10 20 10 100 0 200 units box
region right_fix block 990 1000 0 100 0 200 units box
region right_thermo block 980 990 10 100 0 200 units box
region bottom_fix block 10 990 0 10 0 200 units box
region bottom_thermo block 20 980 10 20 0 200 units box

group tol type 1
group wor type 2

group left_fix region left_fix
group right_fix region right_fix
group bottom_fix region bottom_fix
group left_thermo region left_thermo
group bottom_thermo region bottom_thermo
group right_thermo region right_thermo
group thermolayer union bottom_thermo left_thermo
group boundary union right_fix left_fix bottom_fix thermolayer
group mobile subtract wor boundary

temperature control

compute new mobile temp
compute str wor stress/atom

initial velocities and equilibration

velocity mobile create 300.00 482748 temp new units box

fix 1 wor nve
fix 3 left_fix setforce 0.0 0.0 0.0
fix 200 right_fix setforce 0.0 0.0 0.0
fix 201 bottom_fix setforce 0.0 0.0 0.0
fix 4 mobile temp/rescale 10 300.0 300.0 5.0 1.0
fix_modify 4 temp new
fix 5 thermolayer langevin 300.0 300.0 50.0 48279
thermo 100
thermo_modify lost ignore temp new

timestep 0.001
run 100

velocity tol set 0.0 0.0 0.0 sum no units box
fix 2 tol nve/noforce

thermo 100

run 100

Approaching

velocity tol set 0.0 -700.0 0.0 sum no units box

dump 1 tol cfg 10 dump.tol..cfg id type xs ys zs vx vy vz fx fy fz
dump 2 all cfg 20 dump.all.
.cfg id type xs ys zs vx vy vz fx fy fz
thermo 100
thermo_modify lost ignore temp new
run 100

cutting with tool

velocity tol set 2000.0 0.0 0.0 sum no units box

dump 3 tol cfg 10 dump.tol..cfg id type xs ys zs vx vy vz fx fy fz
dump 4 all cfg 40 dump.all.
.cfg id type xs ys zs vx vy vz fx fy fz
thermo 100
thermo_modify lost ignore temp new
run 400

Thanks for your reply!
Problem description:
I want to use diamond tip to cut silicon workpiece.
    Tip dimension: 10 nm radius.
    Workpiece dimension: 100*187*20 nm
    Input file attached in the end
    Cutting depth: 4.3 nm
      For the cutting process, the normal force( force perpendicular to
workpiece) and driving force ( force along the cutting direction) would not
stabilize in the process. Both of them vary greatly in the process(from 0 nN
to 30,000 nN)

this looks totally unphysical. a few hundred timesteps? is that it??
how *can* this work? where is the equilibration? you assign a
ridiculous velocity. why do you ignore lost atoms? seems like a
typical case of GIGO.

axel.

Thanks for your reply! I am sorry, I am only a newbie.

  1. The experimental velocity is only in Micron/second level, so the velocity is really ridiculous. But I ran this simulation on my PC, this is only a test of my input file.
  2. For the “ignore lost atoms” I found this sentence when I read the Manual “However in some scenarios it may be desirable to only issue a warning or ignore it and skip the computation of the missing bond, angle, etc”.
    I will follow your suggestions and try to run slower velocity with more time steps. Thanks!

And I have another question, I want to add the XY vibration of the tool, and this time I want to set the workpiece move linearly. So I use fix command for both of them. Could I modify the input file like this? I want to calculate the force between the tool and workpiece. Thanks!

3d cutting simulation

units metal
dimension 3
boundary p p p

atom_style atomic
neighbor 4.0 bin
neigh_modify every 2 delay 6 page 50000 one 2000

create diamond tool geometry

region whole block -500 1000 0 120 -400 1000 units box
create_box 2 whole
region tool sphere 250 120 200 30 side in
lattice diamond 3.5667
mass 1 28.085
create_atoms 1 region tool
region Siworkpiece block 0 500 0 100 0 400 units box
lattice diamond 5.43
mass 2 12.010700
create_atoms 2 region Siworkpiece

potential

pair_style tersoff

pair_coeff * * SiC.tersoff C Si

define groups

region left_fix block 0 10 0 100 0 400 units box
region left_thermo block 10 20 10 100 0 400 units box
region right_fix block 490 500 0 100 0 400 units box
region right_thermo block 480 490 10 100 0 400 units box
region bottom_fix block 10 490 0 10 0 100 units box
region bottom_thermo block 20 480 10 20 0 400 units box

group tol type 1
group wor type 2

group left_fix region left_fix
group right_fix region right_fix
group bottom_fix region bottom_fix
group left_thermo region left_thermo
group bottom_thermo region bottom_thermo
group right_thermo region right_thermo
group thermolayer union bottom_thermo left_thermo
group boundary union right_fix left_fix bottom_fix thermolayer
group mobile subtract wor boundary

temperature control

compute new mobile temp
compute str wor stress/atom

initial velocities and equilibration

velocity mobile create 300.00 482748 temp new units box

fix 3 left_fix setforce 0.0 0.0 0.0
fix 200 right_fix setforce 0.0 0.0 0.0
fix 201 bottom_fix setforce 0.0 0.0 0.0
fix 4 mobile temp/rescale 10 300.0 300.0 5.0 1.0
fix_modify 4 temp new
fix 5 thermolayer langevin 300.0 300.0 50.0 48279
fix ro tol move rotate 220 160 200 0.0 1.0 0.0 0.005 units box
fix 2 wor move linear 1000 0 0
thermo 100
thermo_modify lost ignore temp new

timestep 0.001
run 10

velocity tol set 0.0 0.0 0.0 sum no units box
fix 1 tol nve/noforce

thermo 100

run 10

cutting with tool

dump 1 tol cfg 2 dump.tol..cfg id type xs ys zs vx vy vz fx fy fz
dump 2 all cfg 2 dump.all.
.cfg id type xs ys zs vx vy vz fx fy fz
thermo 100
thermo_modify lost ignore temp new
run 40

By the way, I did have tried 1,000 m/s velocity, but just got the same results-----Both the normal force and driving force varied a lot.

By the way, I did have tried 1,000 m/s velocity, but just got the same

mach 3 is still a joke as velocity. also i suspect you don't really
understand the input units.

results-----Both the normal force and driving force varied a lot.

again, with only a few time steps and without proper equilibration,
all you get is garbage.

since you are new to the field, i suggest you take up some classes
and/or get some tutoring from a person that can properly clue you in.
there is no way to do this over a mailing list and also, there is no
point in doing a complex input before you have properly understood the
basics.

axel.

Thank you for your advise!