how to change the properties of the material on the boundary conditions

Hello,

I'm using the uniax.py [1] example to perform some tensile simulation with minor modifications and I would like to ask how to change the material proprietaries only on the boundary layers (i.e on posIds and negIds)? I want to make the Poisson ratio there equal to zero to avoid any deformation.

here is my code:

# -*- encoding=utf-8 -*-
from __future__ import division
from __future__ import print_function

from future import standard_library
standard_library.install_aliases()
from yade import plot,pack,timing
import time, sys, os, copy
#import matplotlib
#matplotlib.rc('text',usetex=True)
#matplotlib.rc('text.latex',preamble=r'\usepackage{concrete}\usepackage{euler}')

# default parameters or from table
readParamsFromTable(noTableOk=True, # unknownOk=True,
 young=24e9,
 poisson=.2,

 sigmaT=3.5e6,
 frictionAngle=atan(0.8),
 epsCrackOnset=1e-4,
 relDuctility=30,

 intRadius=1.5,
 dtSafety=.8,
 damping=0.4,
 strainRateTension=.05,
 strainRateCompression=.5,
 setSpeeds=True,
 # 1=tension, 2=compression (ANDed; 3=both)
 doModes=1,

 specimenLength=.1e-5,
 sphereRadius=3.5e-8,

 # isotropic confinement (should be negative)
 isoPrestress=0,
)

from yade.params.table import *

if 'description' in list(O.tags.keys()): O.tags['id']=O.tags['id']+O.tags['description']

# make geom; the dimensions are hard-coded here; could be in param table if desired
# z-oriented hyperboloid, length 20cm, diameter 10cm, skirt 8cm
# using spheres 7mm of diameter
concreteId=O.materials.append(CpmMat(young=young,frictionAngle=frictionAngle,poisson=poisson,density=4800,sigmaT=sigmaT,relDuctility=relDuctility,epsCrackOnset=epsCrackOnset,isoPrestress=isoPrestress))
sps=SpherePack()
#sp=pack.randomDensePack(pack.inHyperboloid((0,0,-.5*specimenLength),(0,0,.5*specimenLength),.25*specimenLength,.17*specimenLength),spheresInCell=2000,radius=sphereRadius,memoizeDb='/tmp/triaxPackCache.sqlite',returnSpherePack=True)
sp=pack.randomDensePack(pack.inAlignedBox((-.25*specimenLength,-.25*specimenLength,-.5*specimenLength),(.25*specimenLength,.25*specimenLength,.5*specimenLength)) & pack.notInNotch(centerPoint=(.1*specimenLength,0,0),edge=(0,1,0),normal=(0,0,1),aperture=.01*specimenLength),spheresInCell=2000,radius=sphereRadius,rRelFuzz=.4,memoizeDb='/tmp/triaxPackCache.sqlite',returnSpherePack=True)
sp.toSimulation(material=concreteId)
bb=uniaxialTestFeatures()
negIds,posIds,axis,crossSectionArea=bb['negIds'],bb['posIds'],bb['axis'],bb['area']
O.dt=dtSafety*PWaveTimeStep()
print('Timestep',O.dt)

mm,mx=[pt[axis] for pt in aabbExtrema()]
coord_25,coord_50,coord_75=mm+.25*(mx-mm),mm+.5*(mx-mm),mm+.75*(mx-mm)
area_25,area_50,area_75=approxSectionArea(coord_25,axis),approxSectionArea(coord_50,axis),approxSectionArea(coord_75,axis)
O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb(aabbEnlargeFactor=intRadius,label='is2aabb'),],verletDist=.05*sphereRadius),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom(interactionDetectionFactor=intRadius,label='ss2sc')],
  [Ip2_CpmMat_CpmMat_CpmPhys()],
  [Law2_ScGeom_CpmPhys_Cpm()],
 ),
 NewtonIntegrator(damping=damping,label='damper'),
 CpmStateUpdater(realPeriod=.5),
 UniaxialStrainer(strainRate=strainRateTension,axis=axis,asymmetry=0,posIds=posIds,negIds=negIds,crossSectionArea=crossSectionArea,blockDisplacements=True,blockRotations=True,setSpeeds=setSpeeds,label='strainer'),
 PyRunner(virtPeriod=1e-6/strainRateTension,realPeriod=1,command='addPlotData()',label='plotDataCollector',initRun=True),
 PyRunner(realPeriod=4,command='stopIfDamaged()',label='damageChecker'),
]
#O.miscParams=[Gl1_CpmPhys(dmgLabel=False,colorStrain=False,epsNLabel=False,epsT=False,epsTAxes=False,normal=False,contactLine=True)]

# plot stresses in ¼, ½ and ¾ if desired as well; too crowded in the graph that includes confinement, though
plot.plots={'eps':('sigma',)} #,'sigma.50')},'t':('eps')} #'sigma.25','sigma.50','sigma.75')}

O.saveTmp('initial');

O.timingEnabled=False

global mode
mode='tension' if doModes & 1 else 'compression'

def initTest():
 global mode
 print("init")
 if O.iter>0:
  O.wait();
  O.loadTmp('initial')
  print("Reversing plot data"); plot.reverseData()
 else: plot.plot(subPlots=False)
 strainer.strainRate=abs(strainRateTension) if mode=='tension' else -abs(strainRateCompression)
 try:
  from yade import qt
  renderer=qt.Renderer()
  renderer.dispScale=(1000,1000,1000) if mode=='tension' else (100,100,100)
 except ImportError: pass
 print("init done, will now run.")
 O.step(); # to create initial contacts
 # now reset the interaction radius and go ahead
 ss2sc.interactionDetectionFactor=1.
 is2aabb.aabbEnlargeFactor=1.

 O.run()

def stopIfDamaged():
 global mode
 if O.iter<2 or 'sigma' not in plot.data: return # do nothing at the very beginning
 sigma,eps=plot.data['sigma'],plot.data['eps']
 extremum=max(sigma) if (strainer.strainRate>0) else min(sigma)
 minMaxRatio=0.5 if mode=='tension' else 0.5
 if extremum==0: return
 import sys; sys.stdout.flush()
 if abs(sigma[-1]/extremum)<minMaxRatio or abs(strainer.strain)>(5e-3 if isoPrestress==0 else 5e-2):
  if mode=='tension' and doModes & 2: # only if compression is enabled
   mode='compression'
   O.save('/tmp/uniax-tension.yade.gz')
   print("Saved /tmp/uniax-tension.yade.gz (for use with interaction-histogram.py and uniax-post.py)")
   print("Damaged, switching to compression... "); O.pause()
   # important! initTest must be launched in a separate thread;
   # otherwise O.load would wait for the iteration to finish,
   # but it would wait for initTest to return and deadlock would result
   import _thread; _thread.start_new_thread(initTest,())
   return
  else:
   print("Damaged, stopping.")
   ft,fc=max(sigma),min(sigma)
   if doModes==3:
    print('Strengths fc=%g, ft=%g, |fc/ft|=%g'%(fc,ft,abs(fc/ft)))
   if doModes==2:
    print('Compressive strength fc=%g'%(abs(fc)))
   if doModes==1:
    print('Tensile strength ft=%g'%(abs(ft)))
   title=O.tags['description'] if 'description' in list(O.tags.keys()) else O.tags['params']
   print('gnuplot',plot.saveGnuplot(O.tags['id'],title=title))
   print('Bye.')
   O.pause()
   #sys.exit(0) # results in some threading exception

def addPlotData():
 yade.plot.addData({'t':O.time,'i':O.iter,'eps':strainer.strain,'sigma':strainer.avgStress+isoPrestress,
  'sigma.25':forcesOnCoordPlane(coord_25,axis)[axis]/area_25+isoPrestress,
  'sigma.50':forcesOnCoordPlane(coord_50,axis)[axis]/area_50+isoPrestress,
  'sigma.75':forcesOnCoordPlane(coord_75,axis)[axis]/area_75+isoPrestress,
  })
plot.plot(subPlots=False)
#O.run()
initTest()
waitIfBatch()

Best regards,
Mahmoud

[1] https://gitlab.com/yade-dev/trunk/-/blob/master/examples/concrete/uniax.py