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    COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
        Institute for Computational Sciences and Informatics
	                      (CSI 898-Sec 001) 

               Multiscale Simulations of Fracture in Silicon

                             Noam Bernstein
                Center for Computational Materials Science, 
               Naval Research Laboratory, Whashington D. C.

Phenomena such as fracture are controlled by the behavior of materials
at a wide range of length scales.  Strain on the material at the
longest scale what drives the fracture process.  This strain is
relieved when a crack in the material grows, a process which is
controlled by the breaking of interatomic bonds at the crack tip.  The
need to include both the micrometer size (or larger) region which is
under strain, as well as the details of bonding between atoms at the
crack tip, make such multiscale phenomena challenging to simulate.  By
applying appropriate methods to describe different parts of a single
system, from a quantum-mechanical description of the bonding near the
crack tip to continuum elasticity far away from the crack, fracture can
be simulated efficiently.  I describe the methods we use and how we
couple them together to form a single, dynamic simulation.  We apply
the multiscale method to the study of fracture in silicon.  By
straining a sample with a preexisting crack we cause it to grow, and
track its speed and the atomic structure near its tip.  The newly
created surface is initially smooth, but quickly becomes rough as the
material becomes disordered.  We also observe the emission of
dislocations from the crack.  The dislocations move along with the
crack tip, leaving behind an amorphous trail.

	                  Monday , November 8 1999
                                  4:30 pm
                         Room 206, Science & Tech. I

Refreshments will be served.
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Find the schedule at http://www.csi.gmu.edu/lcdm/seminar/schedule.html