Tensile test on aluminum copper CNT nanocomposite

Dear LAMMPS users and developers
I’m conducting a tensile test on Al/Cu alloy reinforced with CNT
The potentials that I have used are

  1. morse potential for the interaction between the C and Al, and between C and Cu

  2. EAM for the interaction between the Al and Cu

  3. and Airebo potential for C C interaction
    The parameters of the morse potential I obtained them from the literature for Al-C and Cu-C
    What I’m expecting to get is an elongation in both the matrix and the CNT until breakage occurs in the matrix followed by a breakage at the CNT
    I’ll explain what I have done so far to achieve this and what were the results

  4. I created the matrix with a hole at its center exactly as the diameter of the CNT and inserted the CNT in it
    the minimization took place as the following

  5. conjugate gradient energy minimization algorithm

  6. the composite was heated from 0 to 700 K then annealed to 300 K using fix tem/rescale

  7. relax the structure at pressure of 0 bar and temperature of 300 K using fix npt
    The result that I got from this is that the atoms of the matrix were causing an early deformation an both end of the CNT during minimization

  8. To fix this I put a gap between the matrix atoms and the CNT, so the hole inside the matrix is larger that the diameter of the CNT, same minimization as above was used
    The result: atoms of the matrix during minimization filled fully or partially the gap between the matrix and the CNT

  9. to fix it, I added a wall at the inner wall of the matrix using the fix wall/region lj93, it was applied on the matrix atoms and the region was of the matrix as well, the minimization was as above
    The result: the CNT moved and got stuck to one side of the matrix

  10. I added a fix move linear on the atoms of the CNT with velocities at x and y were fixed to zero so the cnt will stay at the center of the matrix, same minimization steps as above
    The result: atoms were lost from the CNT

  11. I added the wall/region as above on the inner side of the matrix, and fix move linear on the cnt atoms and did the minimization for the matrix atoms only
    using the following steps of minimization

  12. conjugate gradient energy minimization algorithm

  13. relax the structure at pressure of 0 bar and temperature of 300 K using fix npt

This was followed by removing the fix move linear and minimizing the CNT atoms only
Then the deformation was applied as following

fix 1 all nvt temp 300 300 $(100.0*dt)
fix 3 all deform 1 z erate ${strate} units box remap x

The result: the CNT had perfect structure and stayed at the center after minimization but during deformation instead of having the elongation on the composite, all atoms were moving horizontally and leaving the simulation cell and entering again

  1. In the deformation I changed nvt to fix all langevin
    The result: elongation occurred but it caused a collapse at both ends of the CNT instead of breakage at the center

Please advise


Nothing you are asking about are questions about LAMMPS but questions about how to do your research. Thus you are not likely to get much help on that, since this is off-topic for this forum and more a topic for a discussion with your adviser and collaborators. Please note that most of your “fixes”, i.e. steps 8 and onward read like you are less interested in the science but in computer animation. In general, if something does not behave like you expect it, it is not sufficient to just prevent that from happening, but you first need to understand why. It could just as well be that your expectations are incorrect and not your simulation.