Tensile test on AL Cu/ CNT composite

Dear LAMMPS users

I’m modeling a tensile test on Aluminum copper/CNT composite

the Minimization is achieved by the following stages

min_style cg
minimize 1e-6 1 500000 1000000

timestep 1e-5

fix 1 all temp/rescale 1 0 700 0.02 0.5

fix 2 all nve

run 1000000

unfix 1

unfix 2

reset_timestep 0

timestep 1e-5

fix 1 all temp/rescale 1 700 300 0.02 0.5

fix 2 all nve

run 1000000

unfix 1

unfix 2

reset_timestep 0

timestep 1e-3

fix 1 all npt temp 300 300 $(100.0*dt) aniso 0 0 $(1000.0*dt)

run 100000

I have noticed that the CNT atoms are distorted after the minimization and the CNT is deformed before the tensile force is applied

I have tried to add a fix box/relax iso with a negative pressure to expand the simulation box and allowing the atoms to move to their right position, but it didn’t help at all

Can someone please advice on a way I can follow to further relax the atoms

Regards
Isra

There is not enough information here since your quoted input is incomplete. Atoms go where the forces tell them to go. And those forces are determined by your geometry and the force field.

Thank you for your response

The Al Cu matrix has cylindrical shape with the CNT embedded exactly at the center of the matrix with no gap between the matrix and the CNT
with regards to the interatomic potentials, I have used the following

#####EAM potential for Al-Cu interaction#######
#####AIREBO potetial for C-C atomic bonds#######
#####Morse potential for C-Al interaction#######
#####Morse potential for C-Cu interaction#######
pair_style hybrid eam/alloy airebo 2.0 1 1 morse 2.5 morse 6
pair_coeff * * eam/alloy AlCu.eam.alloy Al Cu NULL
pair_coeff * * airebo CH.airebo NULL NULL C
pair_coeff 1 3 morse 1 0.4691 1.738 2.246
pair_coeff 2 3 morse 2 0.1 1.7 2.22

Hope this helps
Regards
Isra

This all doesn’t matter and there is nothing to add to what I already explained.

I didn’t quite understand what I need to change or add to the code to fix this issue

Well, I don’t know either.
Let me summarize:

  • the choice of fix deform vs. fix npt doesn’t matter since they change the system with the same mechanism
  • how you set up your geometry and force field is your choice and that crucially determines where the atoms “want to go”.

There is no “magic command” that will tell LAMMPS to ignore the physics of your model and instead let the atoms move the way you want them to move. That is the difference between science and computer animation. Now to figure out why exactly atoms move in unexpected or undesired ways, is part of the science/research of your calculation and thus not a LAMMPS issue.

Thank you