Hello everyone,
I am simulating single layer of graphene. I pulled the sheet in x direction with 0.001/ps strain and got the image output from dump image command in LAMMPS. At 32000 steps, I can see bonds are breaking although the stress is only 28 GPa but the stress are not decreasing. I see this happening again on 63000 steps and several other steps before the actual break at 289000 steps. The fracture stress is 172 GPa and strain is 0.289. What can cause the earlier breakage of the bonds?
I have attached the image file here. Thank you for any suggestion.
Dear Baig,
what do you mean by "pulling the sheet in x direction with 0.001/ps strain"? I suppose that you specified the velocity of boundary particles. It is not the best way of simulating quasi-statics. Motion of the boundary causes waves travelling in the material (it could be the reason for bond breakage). The best way to simulate quasi-statiс behavior is the following:
1) impose small uniform affine strain (multiply x coordinates of particles by 1+eps)
2) wait for some time (say 10-100 atomic periods) while material relaxes (uniform affine deformation is not an equilibrium state for the graphene)
3) measure stress
4) repeat step 1
This algorithm allows to avoid waves in the material and to simulate quasi-static behavior.
I have used this algorithm in the attached papers.
Good luck!
Best regards,
Vitaly
Hello Dear Vitaly,
I actually did not impose any velocity on the boundary particles. I generated random velocities in all directions. I used fix deform command to impose an engineering strain along x direction but did not relax the box in intermediate steps. I will try to code your described procedure. Here is some portion of my actual code:
------------Velocity----------------
variable T equal "1000" # Kelvin
velocity graphene create ${T} 12345 temp mobile_temp dist gaussian mom yes rot no
------------Box Deformation--------------------
fix 8 all nvt temp ${temp} ${temp} 5.0 drag 1
fix 9 all deform 1 x erate ${erate1} units box remap x
Dear Vitaly,
Can you give me a link to the paper You were talking about? I did not see any attachment.
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