Dear LAMMPS users and developers,
Recently, I was reading a paper titled “Molecular Dynamics Study on Friction Due to Ploughing
and Adhesion in Nanometric Scratching Process”. It simulates a hard asperity sliding against a soft bulk material in nanoscale. And it classifies the friction into ploughing friction, adhesive friction, and the friction caused by the chips. I would like to figure out how to obtain this ploughing friction, but it seems the paper doesn’t provide the details. Can everyone teach me or give me some clues on how to calculate ploughing friction force in LAMMPS? Thank you.
Sincerely,
Steven
If the paper doesn’t provide all required details, the first step should be to contact the authors and carefully check for supporting information. Often example inputs are provided.
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Actually, I’ve tried to contact the authors, but so far no replies. And I didn’t find any supplemental information on that paper, but thanks for your help.
There should be other, similar papers describing similar or equivalent processes where the information is provided.
If you want more LAMMPS specific help, you need to describe at the very least how this “friction force” is defined. The more specific you can be and the more details you provide, the easier it will be to make some suggestions.
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Yes, I think there should be other similar papers, and I’m working on it.
Yes, you’re right. The thing is I don’t know how this “ploughing friction force” is defined in nanoscale either, or I may have some ideas to calculate it in LAMMPS. How this term is defined in nanoscale is what I want to ask actually.
Thanks for your help!
That is definitely a question that you need to ask domain scientists or learn from publications describing such studies. The fact that you want to apply LAMMPS for such a problem does not automatically mean that other LAMMPS users know about it.
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Yes, you’re right. I will work on it. Thank you so much for your help! Really appreciate it.
One more piece of information from my personal experience. While I am not a domain expert, I once experimented with coupling LAMMPS to a haptic device in order to get a “real feel” for manipulating atoms on the nanoscale: Virtual Atomic Force Microscope using Interactive MD with LAMMPS and VMD - YouTube
However this turned out to be a rather tricky issue. a) it was very difficult to get a stable time integration since the AFM tip is extremely heavy compared to atoms it interacts with so even a slight touching will accelerate them a lot. Add to that the fact that you have no coupling to the outside, so atoms that will be pushed away keep bouncing around the system. For the interactive use, I thus had to apply an (unphysical) dissipative thermostat to remove the excess kinetic energy since those bouncing atoms would have created all kinds of unwanted dynamics. b) the motion of the scratching can realistically only modeled by using a prescribed motion. For the haptic device I had to artificially lower the mass of the AFM tip atoms by multiple orders of magnitude in order to be able to move it at all against the force feedback (in comparison to the buckyballs also included in that system). This is no concern for regular simulations though, but it highlights how “brutal” and “extreme” any such manipulations on the atomic scale can be.
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I just watched that video. It’s really impressive!! Thank you for sharing this and your experience with me. I’ve never seen a simulation like that before. I just started learning MD and LAMMPS. And I think I can learn something from your sharing. Thank you again!