# yade-users team mailing list archive

## Re: [Question #683787]: Using ForceEngine to break a single JCFpm bond

```Question #683787 on Yade changed:

Description changed to:
Hello,

I'm a new user to YADE and I'm in the process of learning about the
JCFpm model. I'm currently trying to break a bond between two particles
using the ForceEngine. As described in the code bit below, I'm trying to
apply and increasing force until a break occurs between the two
particles. The bottom particle is fixed.

If I got the documentation right, the force when the breakage should happen is:
FnMax  = tensileStrength * pi*Rmin^2 [1],[2] -> FnMax = 1e6 * np.pi * pow(0.005,2) =  78.539 N

First question -
For the first trials, I tried using addF manually, using the code below (after running the script). I found that the bond breaks around O.forces.addF(1,(0,0,700)). (I first assumed that addF uses Newtons, but now I'm not so sure...). So, did I calculate FnMax correctly or not?

Second question -
After that, I tried using the ForceEngine (same code, just uncomment #ForceEngine & #PyRunner), increasing the force on the particle, but I can't get it to break. Am I using the engine correctly?

Third question -
I also looked at the InterpolatingDirectedForceEngine [3], where there is a magnitude for the force, but what is the difference between force and magnitudes in the engine (Again, I tried playing with it, with increasing magnitudes, but I still couldn't get it to break)

I would like your help. Sorry if this is too long or if my understanding
of vector physics is a bit lacking :)

### Forces Test 1, YADE ###

import numpy as np

# Define geometry
r = 0.005
intR = 1.0

# Define material
idRockTest = O.materials.append(JCFpmMat(type=1,
young=30e9,
density=2500.0,
poisson=0.1,
tensileStrength=1e6,
cohesion=1e6,
label='Rock'))

O.bodies.append([
sphere((0,0,0),r,material='Rock',color=(0.019, 0.529, 1),fixed=True),
sphere((0,0,2*r),r,material='Rock',color=(1, 0, 0))
])

# Simulation loop
O.engines=[
ForceResetter(),

InsertionSortCollider([Bo1_Sphere_Aabb(aabbEnlargeFactor=intR,label='Saabb')]),

InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom(interactionDetectionFactor=intR,label='SSgeom')],
[Ip2_JCFpmMat_JCFpmMat_JCFpmPhys(cohesiveTresholdIteration=1,label='interactionPhys')],
[Law2_ScGeom_JCFpmPhys_JointedCohesiveFrictionalPM(label='interactionLaw')]
),

# Apply gravity force to particles.
NewtonIntegrator(
gravity=(0,0,-9.81),
damping=0.2),

# Apply force on top particle
#ForceEngine(ids=[1],force=Vector3(0,0,0),label='fEngine'),

#PyRunner(command='fEngine.force[2]+=100',realPeriod=1,initRun=True),

PyRunner(command='recorder()',realPeriod=1,initRun=True),
]

# Define time step
#O.dt = 0.5*utils.PWaveTimeStep()

def recorder():
'i':O.iter,
'F':O.forces.f(1).norm(),
'T':O.forces.t(1).norm()})

plot.plots={'i':('F','T')}
plot.plot()

O.dt=0.

#### manage interaction detection factor during the first timestep and then set default interaction range
O.step();
### initializes the interaction detection factor
SSgeom.interactionDetectionFactor=-1.
Saabb.aabbEnlargeFactor=-1.

# Define time step
O.dt = 0.5*utils.PWaveTimeStep()

O.run()