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CATEGORIES:Monday Mechanics Seminars (DAMTP)
SUMMARY:Elastic moduli of 3-dimensional numerical systems 
 of spheres: comparison with experiments and role o
 f the displacement fluctuations - Ivana Agnolin\, 
 Rennes
DTSTART;TZID=Europe/London:20060220T130000
DTEND;TZID=Europe/London:20060220T140000
UID:TALK4647AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/4647
DESCRIPTION:A study is presented of numerical assemblies of sp
 heres created with the help of different preparati
 on procedures: their elastic moduli crucially depe
 nd on how \nthe samples are created. All samples m
 atch the density of assemblies used during a serie
 s of wave propagation experiments\, but differ in 
 coordination number\, that is not accessible durin
 g experiments. Samples with a low coordination num
 ber show close mechanical properties to the experi
 mental ones\, thus proving that the role of coordi
 nation number dominates on that of density\, contr
 ary to the general belief.  The shear modulus of t
 hose samples shows the 1/4-exponent power law depe
 ndence on pressure also observed during experiment
 s\, in contrast with the 1/6-exponent of the avera
 ge strain assumption.\n\nSuch exponent is related 
 to the displacement fluctuations from the average 
 strain that grains undergo in order to attain equi
 librium. These are the more relevant the smaller t
 he coordination number. They can be decomposed int
 o two distinct contributions\, that we call "struc
 tural" and "residual" fluctuations\, respectively.
  The structural fluctuations depend on the average
  structure of the assembly and determine the macro
 scopic behavior: we will test some of the approach
 es suitable to capture them in the frame of contin
 uum mechanics. On the contrary\, the residual fluc
 tuations\, often dominant in value\, originate in 
 the local deviations from the average geometry and
  contact stiffness\, but have no influence at the 
 macro-scale.
LOCATION:MR4\, DAMTP
CONTACT:Paul Metcalfe
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