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[Rong Zhao <question684078@xxxxxxxxxxxxxxxxxxxxx>]

New question #684078 on Yade:
https://answers.launchpad.net/yade/+question/684078

I am using  TriaxialStressController to conduct the triaxial test numerically. Bur, why is the strain equal to 0 in the triaxial test after the code is implemented?  Here is my code. 

from yade import pack, qt

############################################
###   DEFINING VARIABLES AND MATERIALS   ###
############################################

# The following 5 lines will be used later for batch execution
nRead = readParamsFromTable(
	num_spheres = 1000,  # number of spheres
	compFricDegree = 30, # contact friction during the confining phase
	key = '_triax_base_', # put you simulation's name here
	unknownOk = True
)

from yade.params import table

num_spheres = table.num_spheres  # number of spheres
key = table.key
targetPorosity = 0.43  #the porosity we want for the packing
compFricDegree = table.compFricDegree  # initial contact friction during the confining phase (will be decreased during the REFD compaction process)
finalFricDegree = 30  # contact friction during the deviatoric loading
rate = -0.02  # loading rate (strain rate)
damp = 0.2  # damping coefficient
stabilityThreshold = 0.01  # we test unbalancedForce against this value in different loops (see below)
young = 5e6  # contact stiffness
mn,mx = Vector3(0,0,0), Vector3(1,1,1)  # corners of the initial packing


# create materials for spheres and plates
O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=radians(compFricDegree),density=2600,label='spheres'))
O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=0,density=0,label='walls'))

# create walls around the packing
walls = aabbWalls([mn,mx],thickness=0,material='walls')
wallIds = O.bodies.append(walls)

## use a SpherePack object to generate a random loose particles packing
sp = pack.SpherePack()
sp.makeCloud(mn,mx,-1,0.3333,num_spheres,False, 0.95,seed=1) #"seed" make the "random" generation always the same
O.bodies.append([sphere(center,rad,material='spheres') for center,rad in sp])
 #or alternatively (higher level function doing exactly the same):
 #sp.toSimulation(material='spheres')

############################
###   DEFINING ENGINES   ###
############################

triax = TriaxialStressController(
	maxMultiplier=1.+2e4/young, # spheres growing factor (fast growth)
	finalMaxMultiplier=1.+2e3/young, # spheres growing factor (slow growth)
	thickness=0,
	stressMask=7,
	internalCompaction=True, # If true the confining pressure is generated by growing particles
)

newton = NewtonIntegrator(damping=damp)

O.engines = [
	ForceResetter(),
	InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
	InteractionLoop(
		[Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
		[Ip2_FrictMat_FrictMat_FrictPhys()],
		[Law2_ScGeom_FrictPhys_CundallStrack()]
	),
	GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8),
	triax,
	newton
]

#Display spheres with 2 colors for seeing rotations better
Gl1_Sphere.stripes = 0
if nRead == 0: yade.qt.Controller(), yade.qt.View()

#######################################
###   APPLYING CONFINING PRESSURE   ###
#######################################

#the value of (isotropic) confining stress defines the target stress to be applied in all three directions
triax.goal1 = triax.goal2 = triax.goal3 = -10000

while 1:
  O.run(1000, True)
  ##the global unbalanced force on dynamic bodies, thus excluding boundaries, which are not at equilibrium
  unb = unbalancedForce()
  # print(f"unbalanced force:{unb},mean stress:{triax.meanStress}")
  print 'unbalanced force:',unb,' mean stress: ',triax.meanStress
  if unb < stabilityThreshold and abs(-10000-triax.meanStress)/10000 < 0.001:
  	break

O.save('confinedState'+key+'.yade.gz')
print "###      Isotropic state saved      ###"

###################################################
###   REACHING A SPECIFIED POROSITY PRECISELY   ###
###################################################

import sys #this is only for the flush() below
while triax.porosity > targetPorosity:
	## we decrease friction value and apply it to all the bodies and contacts
	compFricDegree = 0.95*compFricDegree
	setContactFriction(radians(compFricDegree))
	print "\r Friction: ",compFricDegree," porosity:",triax.porosity,
	sys.stdout.flush()
	O.run(500,1)

O.save('compactedState'+key+'.yade.gz')
print "###    Compacted state saved      ###"

##############################
###   DEVIATORIC LOADING   ###
##############################


triax.internalCompaction=False

# Change contact friction (remember that decreasing it would generate instantaneous instabilities)
setContactFriction(radians(finalFricDegree))

# set stress control on x and z, we will impose strain rate on y
triax.stressMask = 5
# now goal2 is the target strain rate
triax.goal2 = rate
# we define the lateral stresses during the test, here the same 10kPa as for the initial confinement.
triax.goal1=-10000
triax.goal3=-10000

# we can change damping here. What is the effect in your opinion?
newton.damping=0.1

O.engines= O.engines + [PyRunner(iterPeriod=20,command='history()',label='recorder')]

# Save temporary state in live memory. This state will be reloaded from the interface with the "reload" button.
O.saveTmp()

#####################################################
###    Record and plot data     ###
#####################################################

from yade import plot

# a function saving variables
def history():
	plot.addData(
		e11=-triax.strain[0],e22=-triax.strain[1],e33=-triax.strain[2],
		s11=-triax.stress(triax.wall_right_id)[0],
		s22=-triax.stress(triax.wall_top_id)[1],
		s33=-triax.stress(triax.wall_front_id)[2],
		DeviatorStress=(-triax.stress(triax.wall_top_id)[1]-(-triax.stress(triax.wall_right_id)[0]-triax.stress(triax.wall_front_id)[2])/2)*1e-6,
		i=O.iter
	)


plot.plots={'i':('s11','s22','s33'),'i ':('e11','e22','e33')}
plot.plot()

O.run()


Thanks!

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