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## [Question #678440]: young in PeriTriaxController

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```New question #678440 on Yade:
https://answers.launchpad.net/yade/+question/678440

Hi,

That's my other question.  (https://answers.launchpad.net/yade/+question/678348)

Let me give another example.Copying script from (https://yade-dev.gitlab.io/trunk/tutorial-examples.html)

Using my own custom materials.

materials.append(FrictMat(young=64e9,poisson=0.12,density=2650,frictionAngle=0.23)

In the second compression, change triax.maxStrainRate=(0,0,0).If I adjust young's modulus to young=64e7, it can maintain the stress of the first isotropic compression, otherwise the stress becomes 0.

I wonder why young's modulus can cause such a big change? How can I adjust:)

Thanks

#####################
# encoding: utf-8

sigmaIso=-1e5

#import matplotlib
#matplotlib.use('Agg')

# generate loose packing
from yade import pack, qt, plot

O.periodic=True

sphere=O.materials.append(FrictMat(young=64e9,poisson=0.12,density=2650,frictionAngle=0.23,label='sphere'))
sp=pack.SpherePack()
sp.makeCloud((0,0,0),(2,2,2),rMean=.1,rRelFuzz=.3,periodic=True)
sp.toSimulation()

O.engines=[
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom()],
[Ip2_FrictMat_FrictMat_FrictPhys()],
[Law2_ScGeom_FrictPhys_CundallStrack()]
),
PeriTriaxController(label='triax',
# specify target values and whether they are strains or stresses
goal=(sigmaIso,sigmaIso,sigmaIso),stressMask=7,
# type of servo-control
dynCell=True,maxStrainRate=(10,10,10),
# wait until the unbalanced force goes below this value
maxUnbalanced=.1,relStressTol=1e-3,
# call this function when goal is reached and the packing is stable
doneHook='compactionFinished()'
),
NewtonIntegrator(damping=.2),
PyRunner(command='addPlotData()',iterPeriod=100),
]
O.dt=.5*PWaveTimeStep()

def addPlotData():
plot.addData(unbalanced=unbalancedForce(),i=O.iter,
sxx=triax.stress[0],syy=triax.stress[1],szz=triax.stress[2],
exx=triax.strain[0],eyy=triax.strain[1],ezz=triax.strain[2],
# save all available energy data
Etot=O.energy.total(),**O.energy
)

# enable energy tracking in the code
O.trackEnergy=True

# define what to plot
plot.plots={'i':('unbalanced',),'i ':('sxx','syy','szz'),' i':('exx','eyy','ezz'),
# energy plot
' i ':(O.energy.keys,None,'Etot'),
}
# show the plot
plot.plot()

def compactionFinished():
# set the current cell configuration to be the reference one
O.cell.trsf=Matrix3.Identity
# change control type: keep constant confinement in x,y, 20% compression in z
triax.goal=(sigmaIso,sigmaIso,-.2)
triax.stressMask=3
# allow faster deformation along x,y to better maintain stresses
triax.maxStrainRate=(0,0,0)
# next time, call triaxFinished instead of compactionFinished
triax.doneHook='triaxFinished()'
# do not wait for stabilization before calling triaxFinished
triax.maxUnbalanced=10

def triaxFinished():
print 'Finished'
O.pause()

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