# yade-users team mailing list archive

## [Question #677194]: Unstable clump

```New question #677194 on Yade:

Hi guys,

I tried to model a single particle crushing test form a clump (used CohfrictMat contact model), for initial step, everything looks good but when I run the model the Clump (cluster) collapses immediately in initial stages. Does anyone know how I can settle this issue?

Hessam

Part of my code:

# encoding: utf-8

from yade import pack, utils, ymport, export
import numpy as np
import matplotlib.pyplot as plt
import os.path

try:
os.mkdir('VTKFiles')
except:
pass

#cell geomtry
# cell dimentions
sp=ymport.textExt('ClumpSpheres-57Spheres.spheres', 'x_y_z_r',color=(0,0.3,0.6))

mn=[]; mx=[]
for i in [0,1,2]:

#Approximate center of Clump
Circen=((mn[0]+mx[0])/2,(mn[1]+mx[1])/2,(mn[2]+mx[2])/2)

#Changing the dimension of the CLump to desired size.

# changing the positions, radiuses of the spheres and the cell dimentions to desired scale.
for b in sp:
b.state.pos*=SizeR

mn=[SizeR*b for b in mn]
mx=[SizeR*b for b in mx]

#  M.A: Hessam you should be more confident about the selection of loading rate. Note to have enough reasons.
displacementRate = 1.6667e-6 # m/s

young =3e8
poisson = 0.25
density = 1950
frictionAngle = 20
normalCohesion = 70e9
output='./out/'+identifier
rate = abs(mn[1]-mx[1])*0.01# you should change it
stabilityThreshold=0.01
iterper=1000
shearCohesion=20e9

#frictionless walls

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

# M.A: Hessam you can not use your previous command yimport .... since the bodies geometry has been changed.
for b in sp:

triax = TriaxialStressController(
thickness=0,
internalCompaction=False,
)

O.engines=[
ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
[Ip2_FrictMat_FrictMat_FrictPhys(),Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(label="cohesiveIp")],
[Law2_ScGeom_FrictPhys_CundallStrack(),Law2_ScGeom_CohFrictPhys_CohesionMoment(
useIncrementalForm=True, #useIncrementalForm is turned on as we want plasticity on the contact moments
always_use_moment_law=False, #if we want "rolling" friction even if the contact is not cohesive (or cohesion is broken), we will have to turn this true somewhere
label='cohesiveLaw')]
),
GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.5),
triax,
VTKRecorder(iterPeriod=iterper,initRun=True, Key=identifier, fileName='VTKFiles/'+'-', recorders=['all']),
NewtonIntegrator(damping=0.9)
]

O.dt = 0.3 * utils.PWaveTimeStep()

--