Dear Lammps Users,
I am using Lammps to simulate the compression test on copper single crystal and polycrystal samples at 300K. In the beginning, I used 16 nodes to run the simulation. When I used a bigger sample for the same simulation, I had to use 64 nodes to run the same simulation. I plotted the stress-strain curve for both the results and surprisingly there was a big difference between them. As you can see from the attached graph, for 16 nodes, the yield strength of single crystal is smaller than that of polycrystal. But for 64 nodes, the yield strength of single crystal is much bigger than that of polycrystal. Now this makes the situation totally contradictory as the polycrystal’s result can either be smaller or bigger than the single crystal’s, and not be both.
I noticed in the Lammps website, there are some discussions about the problems of using different numbers of processors. I had used “velocity” command in my simulation so, I tried to change the “Loop” option from “all” to “geom” but it still gave the same problem with the curves. I also tried to use “read_data” instead of “create_atoms” to create my single crystal sample but in vain.
I would really appreciate if you could provide me with some suggestions to fix this problem.
Thanks a lot for your time.
Shuyin
comparison.pdf (124 KB)