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[Christian Sommerfeld <question211358@xxxxxxxxxxxxxxxxxxxxx>]

Question #211358 on Yade changed:
https://answers.launchpad.net/yade/+question/211358

Christian Sommerfeld posted a new comment:
Hi,

@Chareyre: i measured the force with a load cell.

I did a Calculation of the normal force  and i get a force of 365 N. But this is not the force i want to measure. So i took a look on the wiki page of contact mechanics  http://en.wikipedia.org/wiki/Contact_mechanics  
So i implemented the force into my code and  i get nearly the force that i'm looking for. 


from yade import  plot, geom, utils

#parameters:

r1 = 0.003
r2 = 0.003
E1 = 210e9
E2 = 90e9
poisson1 = 0.3
poisson2 = 0.14
frictionAngle = .5
density1 = 7900
density2 = 2500
g = 9.81
h = 0.1

#computation:

k1 = 2*E1*r1
k2 = 2*E2*r2

kn = (k1*k2)/(k1+k2)

V1 = 4.0/3.0*math.pi*r1*r1*r1
V2 = 4.0/3.0*math.pi*r2*r2*r2

#m1 = density1*V1
m2 = density2*V2 

m1 = 0.0004

Epot = m1*g*h

d = ((2*Epot)/kn)**(1/2.0)

Etot = 1.0/((1.0-poisson1**(2.0))/E1+((1.0-poisson2**(2.0))/E2))

Fres = 4.0/3.0*Etot*r1**(1.0/2.0)



O.materials.append(FrictMat(young=E1,poisson=poisson1,frictionAngle=frictionAngle,density=density1, label='mat_ground'))

O.materials.append(FrictMat(young=E2,poisson=poisson2,frictionAngle=frictionAngle,density=density2,
label='mat_spheres'))

O.bodies.append(utils.sphere([0,0,0.103],0.003,color=[1,1,0],
material='mat_spheres'))

O.bodies.append(utils.sphere([0,0,0.003],0.003,color=[1,1,1],
fixed=True, material='mat_ground'))

O.engines=[
   ForceResetter(),
   InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb()]),
   InteractionLoop(
      [Ig2_Sphere_Sphere_ScGeom(),Ig2_Facet_Sphere_ScGeom()],
      [Ip2_FrictMat_FrictMat_FrictPhys()],
      [Law2_ScGeom_FrictPhys_CundallStrack()]

   ),
  NewtonIntegrator(damping=0.5, gravity=(0,0,-9.81)),
 PyRunner(iterPeriod=5,command="myAddPlotData()")
]

O.dt=1*utils.PWaveTimeStep()

def myAddPlotData():
	force=plot.addData(t=O.time,F=(O.forces.f(0).norm()/kn)**(3.0/2.0)*Fres)

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

from yade import qt
v=qt.View()

Now i have two question: 1. What is the physical meaning of the normal
force from cundall and strack? Why is that force so high for a ball with
a radius of 3 mm

2. If i want to calculate the normal stiffness kn i need a length
proportional to the radius from both bodies. Like for a sphere k=E*2*r.
How can i obtain this lenght for  a facetcylinder? Is this the radius of
the base?

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