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   COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS        
                   School of Computational Sciences	
                           (CSI 898-Sec 001) 
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                      Smart Nonlinear Modeling:
               Dislocations and the Martensitic Embryo

                            Andrew Reid
 Materials Science Department, Northwestern University, Chicago, Ill

The Martensitic phase transition is one in which a solid undergoes 
a first-order change in crystalline structure.  This transition 
occurs by a process of nucleation and growth, but Martensite 
particles are mechanically constrained by the host matrix, a 
combination of features which has presented a considerable challenge 
to theorists and modelers for many years. The on-going large 
increases in available computer power have motivated new modeling 
approaches in materials science, which have begun to close the
gap between the various length scales.  Some investigators have 
had notable success building heterogeneous multi-scale model systems, 
in which methods which explicitly model individual atoms are directly 
combined with more traditional finite-element type mechanical models.
Another approach, which will be the focus of this presentation, is 
to take a conventional large length-scale modeling technique and 
enrich it with additional degrees of freedom, thus creating what
may be called a "smart" mesoscopic model.  The extra degrees of 
freedom account for the mesoscopic effects of physical processes 
whose origin lies at length scales not directly accessible to the model.
In the current example, discrete dislocations are added to a fully 
nonlinear, nonlocal continuum elastic model of the Martensitic 
phase transition, in order to gain some insight into the 
relationship between the geometry of dislocation arrays and their kinetic
role in the nucleation of Martensite.  The new model suggests that 
pretransformation phenomena known as "embryos" may be quite common.

                        Monday , October 16, 2000
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served at 4:15 PM.
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Find the schedule at http://csi.gmu.edu/lcdm/seminar/schedule.html