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SUMMARY:Shock Compression of Metals: From Monocrystals to Nanocrystals\, f
 rom Explosives to Lasers - Marc André Meyers\, University of California S
 an Diego
DTSTART:20080923T123000Z
DTEND:20080923T133000Z
UID:TALK13574@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:Shock compression creates a state of uniaxial strain in which 
 large deviatoric stresses\, far surpassing the material strength\, are gen
 erated. Ductile metals respond by the (profuse) generation and (limited) m
 otion of dislocations. There is also an associated temperature increase\, 
 that seems\, in a few cases\, to significantly exceed the Rankine-Hugoniot
  predictions.\nWe have subjected metallic specimens (copper\, nickel\, and
  vanadium) to high-amplitude shock waves using explosives\, gas-guns\, and
  lasers. The pulse durations varied from a few microseconds to a few nanos
 econds.\nThe predictions of molecular dynamics computations are compared w
 ith post-shock experimental measurements by transmission electron microsco
 py and there is an equivalence in the results. However\, the defect spacin
 gs differ by orders of magnitude. This conundrum is resolved through the s
 uggestion that most dislocations generated in shock compression are annihi
 lated during the release and post-release portion. \nTime permitting\, rec
 ent results on laser-induced fragmentation on vanadium will be presented.\
 n
LOCATION:The Committee Room\, The Bragg Building\, Cavendish Laboratory\, 
 Department of Physics
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