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[Bruno Chareyre <question269063@xxxxxxxxxxxxxxxxxxxxx>]

Question #269063 on Yade changed:
https://answers.launchpad.net/yade/+question/269063

Bruno Chareyre proposed the following answer:
>So is it correct to apply force (pressure) to sphere without taking
into account it's size, or i need to multiply by it's radius, diameter
or volume?

None of them ;)
You need to multiply pressure by area, as always. When you change the size of spheres you also change the thickness of the plate.

>Also Bruno about your formula macroStress =
sphereStress*sphereVolume/cubeVolume. How it will work for non regular
packing?

https://yade-dem.org/doc/user.html?highlight=microstress#micro-stress-
and-micro-strain

>Yes Ansys solution is exact for uniaxial tension

I don't think Ansys gives the displacement field that you can derive analyticaly for a sphere array. It gives the exact solution for a homogeneous isotropic material, instead. I really mean to write on the paper the displacement of each sphere in an array, you don't need DEM for that.
Exemple for a single chain of spheres (diameter D) where sphere 0 is fixed, the displacement of sphere "i" is:
u[i]=F/kn*i

An equivalent expression exhibits equivalent stress and strain:
u[i]/(iD)=F/(kn*D) = F/D² * 1/Young
since kn (contact stiffness) is defined as kn=Young*D.
The meaning of this last one is strain=stress/Young

You should go through this type of thing to understand how DEM will or
will not do what you expect. It will also help clarify what is strain
and what is stress.

Besides I vote as Jan suggests about closing this discussion.

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