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[mohsen <question403385@xxxxxxxxxxxxxxxxxxxxx>]

Question #403385 on Yade changed:
https://answers.launchpad.net/yade/+question/403385

mohsen posted a new comment:
Hi Jan

>could you please provide a MWE (how you evaluate "determined" and
>"computed" E and nu ).

E and nu are the parameters which CPM material needs. Hence the phrases 'inter particle E and nu' or 'mecro ' are clearer! Surrey for wrong phrase! 
Computed E and nu are calculated after axial loading (z axis) up to special strain (1e-2) as follows:
E=slope of sigma-epsilon graph
nu= - 0.5(epsx+epsy)/(epsz)

>Next time plese be more specific what "great difference" is (10%? 1000%?)
Yes depending on geometry it can be in the order of 1000% or even more!

Can we set a geometry which lead to macro parameters the same as micro ones?
I could not set it till now. It may be because of high desired nu which is near 0.35. Setting inter-particle nu as 0.35 causes large values of E which seems correct; however it is not may case

>do you mean that you set CpmMat(...,young=25e9) and macroscopic Young's
>modulus would be 25 GPa? 
Yes
>For sure there exists suxh geometry, but it would be very special case.
For cylinder with height to diameter ratio of two, I have not found such geometry till now. Also it may be interesting for you to check [3]. They could not achieve a set of inter particle parameters (E, nu, phi) that matches the macro ones. I think it is also the case for [2]. 

What do you think am i right?
Can we say: It is very hard to find a geometry satisfying this hypothesis: 'micro and macro parameters are the same'. If it is true then:

'Is there any reference that can interpret the difference between micro
and macro parameters theoretically '? Is it a usual case in DEM
modeling?

Anyway, my question finds still no answer: In references [1] and [2]
have they compared values of micro and macro E and nu? I could not find
any details about geometry in [2].


[3] : Wang X L, Li J C. Simulation of triaxial response of granular materials by modified DEM. Sci China-Phys Mech Astron, 2014, 57: 22972308, doi:
10.1007/s11433-014-5605-z

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