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SUMMARY:Nonlocality and dynamic fracture: Are multiscale models the answer
  in dynamic fracture? - Florin Bobaru\, Department of Engineering Mechanic
 s\, University of Nebraska-Lincoln
DTSTART:20081021T123000Z
DTEND:20081021T133000Z
UID:TALK14440@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:Dynamic fracture is a complex phenomenon driven by what happen
 s in a finite volume around the crack tip. Under sufficiently fast loading
  conditions a straight crack branches into two (and sometimes more) cracks
  that move along with speeds measured to be no more than 10% less than the
  speed measured just before branching. In spite of sustained efforts from 
 the computational modeling and simulation community for the past few decad
 es\, the challenging problem of dynamic crack branching in brittle plates 
 has not had a satisfactory solution. Existing solutions may show branching
  of the crack path\, but the obtained crack propagation speeds are complet
 ely different from the measured values. Difficulties with mesh dependency 
 and lack of convergence are also noticed. It has been recently argued that
 \, in order to simulate dynamic fracture\, multiscale models (coupling ato
 mistic and continuum zones) may be needed. However\, the “process zone
 ” in dynamic crack branching\, for example\, may be in the order of mill
 imeters and the time scales in the order of microseconds. These scales ren
 der a multiscale approach\, even if possible\, rather impractical\, using 
 the existing computational resources.\nNonlocal models are better able to 
 eliminate mesh dependency and convergence problems in problems involving d
 amage. The new peridynamic method\, a reformulation of classical continuum
  mechanics proposed by Silling in 2000\, is used here to obtain the first 
 correct prediction by computational simulation of the velocity profile and
  crack paths in dynamic crack branching of thin brittle plates. In peridyn
 amics cracks are generated\, propagate\, and interact in an autonomous way
 . We like to say that in peridynamics cracks are not part of the problem\,
  they are part of the solution. I will also show how adaptive refinement c
 an be developed for this nonlocal method and give an example of mixed-mode
  fracture (the four-point bending problem).\nIn the introduction\, I will 
 also give an overview of other research areas in my group: shape optimizat
 ion and the shape of stegosaurus’ cooling plates\, flexing granular mate
 rials and particle-size dependence\, enhancing mixing and segregation in g
 ranular matter\, penetration in granular materials\, etc.\n
LOCATION:The Committee Room\, Bragg Building\, Cavendish Laboratory\, Depa
 rtment of Physics
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