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[behzad majidi <question248206@xxxxxxxxxxxxxxxxxxxxx>]

New question #248206 on Yade:
https://answers.launchpad.net/yade/+question/248206

Hi,

Imagine we have a material sample composed of let's say five spheres with the same radius of 1, touching in line creating a a vertial beam. (as given below)
We put this sample between two facets and apply a certain velocity to the facet(s) to compress the sample. 
So, it's a simple compression test on a sample. 
I wonder how can we plot the stress-strain curve of this sample. 
I guess it can work if I put;

stress=utils.bodyStressTensors()
 and then I call for stress[box_2[[2][2] it should work.
But how this stress is calculated? Does Yade get it from the area estimated from the sphere/facet penetration? 
If it's the case what happens if the sample is composed of a random packing of spheres making a cylinder? Does Yade calculate the stress automatically from each contacting spheres or I need to get the force on the facet and then divide it by the area of the sample?

=======================
O.reset()
from yade import utils, plot
from yade import pack, qt


id_Mat1=O.materials.append(FrictMat(young=1e8,poisson=0.3,density=1000,frictionAngle=1))
Mat=O.materials[id_Mat1]

id_Mat2=O.materials.append(FrictMat(young=1e10,poisson=0.3,density=1000,frictionAngle=1))
Rigid=O.materials[id_Mat2]


s1=utils.sphere([0.0,0.0,1.0],1.0,fixed=True,material=Mat)
s2=utils.sphere([0.0,0.0,3.0],1.0,fixed=True,material=Mat)
s3=utils.sphere([0.0,0.0,5.0],1.0,fixed=True,material=Mat)
s4=utils.sphere([0.0,0.0,7.0],1.0,fixed=True,material=Mat)
s5=utils.sphere([0.0,0.0,9.0],1.0,fixed=True,material=Mat)

O.bodies.append(s1)


box_1 = O.bodies.append(box((0,0,0),(1,1,.001),fixed=True,material=Rigid))
box_2 = O.bodies.append(box((0,0,10.0),(1,1,.0001),fixed=True,material=Rigid))

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()]
),
NewtonIntegrator(damping=0.7,gravity=[0,0,0]),
PyRunner(command='AutoData()',iterPeriod=1000)
]


O.bodies[box_2].state.vel=(0,0,-0.001)

qt.View()

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