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SUMMARY:Shocks in fragile matter - Professor Vincenzo Vitelli\, Instituut-
 Lorentz for theoretical physics\, Leiden University\, The Netherlands
DTSTART:20120518T130000Z
DTEND:20120518T140000Z
UID:TALK37978@talks.cam.ac.uk
CONTACT:Tracy Inman
DESCRIPTION:Non-linear sound is an extreme phenomenon typically observed i
 n solids after violent explosions. But granular media are different. Right
  when they unjam\, these fragile and disordered solids exhibit vanishing e
 lastic moduli and sound speed\, so that even tiny mechanical perturbations
  form supersonic shocks. Here\, we perform simulations in which two-dimens
 ional jammed granular packings are continuously compressed\, and demonstra
 te that the resulting excitations are strongly nonlinear shocks\, rather t
 han linear waves. We capture the full dependence of the shock speed on pre
 ssure and compression speed by a surprisingly simple analytical model. We 
 also treat shear shocks within a simplified viscoelastic model of nearly-i
 sostatic random networks comprised of harmonic springs. In this case\, anh
 armonicity does not originate locally from nonlinear interactions between 
 particles\, as in granular media\; instead\, it emerges from the global ar
 chitecture of the network. As a result\, the diverging width of the shear 
 shocks bears a nonlinear signature of the diverging isostatic length assoc
 iated with the loss of rigidity in these floppy networks
LOCATION:Small Lecture Theatre\, Cavendish Laboratory
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