Contact model for differentiating between static and dynamic friction

Hi Paul,

I think that there is no ready-for-use function, but you can try to periodically inspect simulations to check whether they are sliding (e.g. Ip2_FrictMat_FrictMat_MindlinPhys() provides 'isSliding' parameter). First I would try to modify the interactions with a Python function. See example code below.

Cheers,
Karol

############
from yade import plot
###### PARAMS
mu_static = 0.8
mu_dynamic = 0.5

angle_static = atan(mu_static)
angle_dynamic = atan(mu_dynamic)

##### FUNCTIONS
def check_interactions():
    for ii in O.interactions:
        if ii.phys.isSliding:
            ii.phys.tangensOfFrictionAngle = mu_dynamic
        """ uncomment this part if it is logical in your case that interaction becomes static again
        else:
            ii.phys.tangensOfFrictionAngle = mu_static
        """

###### MATERIALS
O.materials.append(FrictMat(label='static'))
O.materials['static'].frictionAngle = angle_static

###### BODIES
sp1 = O.bodies.append(sphere((0,0,0),0.1, fixed = True, material = O.materials['static']))
sp2 = O.bodies.append(sphere((0,0.199,0),0.1, fixed = True, material = O.materials['static']))

# rotate one sphere
O.bodies[sp2].state.angVel = (5e-5,0,0)

###### ENGINES

O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb()]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_MindlinPhys()],
  [Law2_ScGeom_MindlinPhys_Mindlin()],
 ),
 NewtonIntegrator(),
 PyRunner(command = "plot.addData(t = O.time, F = O.interactions[0,1].phys.shearForce.norm())", virtPeriod = 1),
 PyRunner(command = "check_interactions()", iterPeriod = 100),#
]

O.dt = PWaveTimeStep()*0.5

plot.plots = {'t':'F'}
plot.plot()

O.run()

Thanks Karol Brzezinski, that solved my question.

Thanks for your feedback, Karol and thanks for the sample code,

that helped me a lot and also answered my question so far. I just have a small question about this, which is rather less related to the friction value itself:
Why does the rotational speed of the particle sp1 not decrease despite the counteracting friction force. How can friction dissipation be activated in the Mindlin-material-model?

In addition, for future readers, I would like to extend the above example in the code shown below to include the friction values from the different material pairings distinguished in my other question.

With best wishes, Paul

############
from yade import plot
###### PARAMS
mu_static00 = 0.8
mu_static01 = 0.4
mu_static11 = 0.1
mu_dynamic00 = 0.5
mu_dynamic01 = 0.3
mu_dynamic11 = 0.1

##### FUNCTIONS
def check_interactions():
    for i in O.interactions:
        b1, b2 = O.bodies[i.id1],O.bodies[i.id2]
        if i.phys.isSliding:
            if b1.mat.id == idMat0 and b2.mat.id == idMat0:
                i.phys.tangensOfFrictionAngle = mu_dynamic00
            elif (b1.mat.id == idMat0 and b2.mat.id == idMat1) or (b1.mat.id == idMat1 and b2.mat.id == idMat0):
                i.phys.tangensOfFrictionAngle = mu_dynamic01
            elif b1.mat.id == idMat1 and b2.mat.id == idMat1:
                i.phys.tangensOfFrictionAngle = mu_dynamic11
            else:
                print("Kombination Gleitreibpartner nicht vorgesehen")
        else:
            if b1.mat.id == idMat0 and b2.mat.id == idMat0:
                i.phys.tangensOfFrictionAngle = mu_static00
            elif (b1.mat.id == idMat0 and b2.mat.id == idMat1) or (b1.mat.id == idMat1 and b2.mat.id == idMat0):
                i.phys.tangensOfFrictionAngle = mu_static01
            elif b1.mat.id == idMat1 and b2.mat.id == idMat1:
                i.phys.tangensOfFrictionAngle = mu_static11
            else:
                print("Kombination Haftreibpartner nicht vorgesehen")

###### MATERIALS
idMat0 = O.materials.append(FrictMat(frictionAngle = atan(mu_static00), label='Mat0'))
idMat1 = O.materials.append(FrictMat(frictionAngle = atan(mu_static11), label='Mat1'))

###### BODIES
sp1 = O.bodies.append(sphere((0,0,0),0.1, fixed = True, material = O.materials['Mat0']))
sp2 = O.bodies.append(sphere((0,0.199,0),0.1, fixed = True, material = O.materials['Mat1']))

# rotate one sphere
O.bodies[sp1].state.angVel = (2.5e-3,0,0)

###### ENGINES
O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb()]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_MindlinPhys()],
  [Law2_ScGeom_MindlinPhys_Mindlin()],
 ),
 NewtonIntegrator(),
 PyRunner(command = "plot.addData(t = O.time, F = O.interactions[0,1].phys.shearForce.norm(), v1 = O.bodies[sp1].state.angVel[0], v2 = O.bodies[sp2].state.angVel[0])", virtPeriod = 1),
 PyRunner(command = "check_interactions()", iterPeriod = 100),#
]

O.dt = PWaveTimeStep()*0.5

plot.plots = {'t':(('F','b-'),None,('v1','g--'),('v2','r--'))}
plot.plot(subPlots = False)

O.run()

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