Different friction for different stl

Hi,
I'd like to use different friction for different stl.
For example I'd like to set friction on stl 1 grater than stl 2.
I tried something like:
fix cad1 all mesh/gran/stressanalysis stl1.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix cad2 all mesh/gran/stressanalysis stl2.stl 2 0.001 0. 0. 0. 0. 0. 0.
But it request me 2 atom types.
Have I to set 2 atom types?
If yes, how have I to set the friction between the 2 types: fix fr all property/global coefficientFriction peratomtypepair 2 value_11 value_12 value_21 value_22 ?

Thanks for any help

Andrea

Forums:

LIGGGHTS® - User Forum

raguelmoon | Tue, 05/03/2011 - 14:32

Hi, you should define two

Hi,
you should define two types of particles: type 1 and type 2; and then define material properties for each. For two different frictions, you use this:

fix m5 all property/global coefficientFriction peratomtypepair 2 0.5 0.0 0.0 0.0

where the friction between particles type 1 and 1 is 0.5 while between type 1 and 2 is 0.0. Now, you can use these material for your wall or particle.
Best,
Ram

andrea.pasquali | Tue, 05/03/2011 - 15:27

If I understood well I have

If I understood well I have to write:

fix m5 all property/global coefficientFriction peratomtypepair 2 0.5 0.0 0.0 0.01

and then:

fix cad1 all mesh/gran/stressanalysis stl1.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix cad2 all mesh/gran/stressanalysis stl2.stl 2 0.001 0. 0. 0. 0. 0. 0.

In this way I will have friction 0.5 between particles and cad1 and 0.01 between particles and cad2?
Between particles friction will be 0. Is it correct?
When I use friction for 1 type of particles, like:

fix m5 all property/global coefficientFriction peratomtypepair 1 0.5

also the friction between particles iz zero?

Thanks
Andrea

raguelmoon | Wed, 05/04/2011 - 13:53

Hi, >>When I use friction for

Hi,
>>When I use friction for 1 type of particles, like:
>>fix m5 all property/global coefficientFriction peratomtypepair 1 0.5
>>also the friction between particles iz zero?

no, the friction between particles is 0.5. For your case, you have to define three materials, one for particles, one for cad1 and one for cad2. And, use this logic to apply friction:

11 12 13 21 22 23 31 32 33

Where 11 is friction between particles and 12 between particles and cad1 and 13 between particles and cad2 and so on..
Best,
Ram

andrea.pasquali | Wed, 05/18/2011 - 18:09

Hi, Finally I used: fix m4

Hi,
Finally I used:

fix m4 all property/global coefficientFriction peratomtypepair 2 0.3 0.001 0.001 0.001
...
fix cad1 all mesh/gran/stressanalysis cad1.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix cad2 all mesh/gran/stressanalysis cad2.stl 2 0.001 0. 0. 0. 0. 0. 0.

In this way cad1 has friction 1 = 0.3 (like particles) and cad2 has friction 2 = 0.001, right?
I have another question about different material for walls.
If I write:

fix boxwalls_x all wall/gran/hertz/history ${fr_w} ${co_w} xplane ${mX} ${pX} 2

also xplane will be the friction 2 = 0.001 ?
I run a simulation with this but it doesn't seem to work properly.

Thanks

Andrea