# [lammps-users] FW: [Needs some ideas]

I’m working on nanmachining. I have a single crystalline copper and

Isn't friction the force that the surface exerts on the workpiece?
I would find some papers that measure surface friction/stiction
and see what they calculate.

Steve

Hi, Mayank. The way to go about this is to either (if you’re very lucky) find someone who’s done similar simulations before, or (usually) to look on search engines like ISI Web of Science, do topic-searches for papers with the relevant keywords, and sift through what you find. Tedious, but that’s the way most people operate.

Best,
Rob

The frictional force would be calculated from dump Force dump files. Where at every time step Fx, Fy, Fz force components on each atom of workpiece and tool dumped out.

Right now I have calculated cutting force and thrust force during cutting by processing the dump files. I made a code which averages the force acting on a atom by other atoms within a certain radius. The cutting force and thrust force all calculated using all atoms of workpiece and tool.

Frictional force is the force applied on tool by workpiece atoms. But for calculating the frictional force I should be considering the atoms near the tool tip (if I’m not wrong). A diamond rigid tool is used. Isn’t the case that I should only be using only one or few layers of tool which are experiencing frictional force?

Some researchers have calculated frictional force as cutting force per unit length (length of cut, in case of indentations). But tool used in my research has same width as workpiece. Can I also calculate frictional force by dividing the cutting force by length of cut?

If this not the case then should I be to only calculating the cutting force experienced by atoms in near proximity of tool? Or only the force exerted by workpiece atoms on tool atoms?

If this is the case I have few questions-:

1. How do I know which atoms of tool and/or workpiece are in cutting region? As I have a dump file for cutting force (and stress), and is there any way in which I can differentiate between these atoms or other atoms?

2. In force dump file force acting Fx, Fy, Fz on each atom at every time step is present. With this I have atom ID and type info. in force dump file. Does Lammps follow some pattern when creating a Copper FCC structure? Like extreme left bottom corner atom is given atom ID ‘1’.

3. Or should I simply divide the cutting force by cutting length?

Thanks
Mayank

1. How do I know which atoms of tool and/or workpiece are in cutting region?
As I have a dump file for cutting force (and stress), and is there any way
in which I can differentiate between these atoms or other atoms?

2. In force dump file force acting Fx, Fy, Fz on each atom at every time
step is present. With this I have atom ID and type info. in force dump file.
Does Lammps follow some pattern when creating a Copper FCC structure? Like
extreme left bottom corner atom is given atom ID '1'.

3. Or should I simply divide the cutting force by cutting length?

I presume you are also dumping the xyz coords of each atom, so most
of your questions seem related to the geometry of your model, which
you setup and therefore should know. If you sum the forces on all
atoms in the workpiece, you get the net force of the substrate on it.
Thus it is OK to include atoms far from the cutting location, b/c forces
between those atoms will cancel. You can also look at compute group/group
which will give you energy/force between 2 groups of atoms (workpiece,
substrate),
but will only work if you are using a pair potential.

Steve