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SUMMARY:Elastic moduli of 3-dimensional numerical systems of spheres: comp
 arison with experiments and role of the displacement fluctuations - Ivana 
 Agnolin\, Rennes
DTSTART:20060220T130000Z
DTEND:20060220T140000Z
UID:TALK4647@talks.cam.ac.uk
CONTACT:Paul Metcalfe
DESCRIPTION:A study is presented of numerical assemblies of spheres create
 d with the help of different preparation procedures: their elastic moduli 
 crucially depend on how \nthe samples are created. All samples match the d
 ensity of assemblies used during a series of wave propagation experiments\
 , but differ in coordination number\, that is not accessible during experi
 ments. Samples with a low coordination number show close mechanical proper
 ties to the experimental ones\, thus proving that the role of coordination
  number dominates on that of density\, contrary to the general belief.  Th
 e shear modulus of those samples shows the 1/4-exponent power law dependen
 ce on pressure also observed during experiments\, in contrast with the 1/6
 -exponent of the average strain assumption.\n\nSuch exponent is related to
  the displacement fluctuations from the average strain that grains undergo
  in order to attain equilibrium. These are the more relevant the smaller t
 he coordination number. They can be decomposed into two distinct contribut
 ions\, that we call "structural" and "residual" fluctuations\, respectivel
 y. The structural fluctuations depend on the average structure of the asse
 mbly and determine the macroscopic behavior: we will test some of the appr
 oaches suitable to capture them in the frame of continuum mechanics. On th
 e contrary\, the residual fluctuations\, often dominant in value\, origina
 te in the local deviations from the average geometry and contact stiffness
 \, but have no influence at the macro-scale.
LOCATION:MR4\, DAMTP
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