Dislocations, their dynamics, and their organization into patterns
represent
a system of great importance, not only for materials structure, but for
broader questions such as melting, the nature of glassy materials, and
systems with competiting interactions.
In the context of friction, two crystalline materials sheared
against each other work harden and form microstructure over time.
The grain boundaries composing this microstructure
are constructed from dislocations that have emerged from the
interface and coalesced in a process that remains poorly understood.
Dislocations are also known to play an important role in the melting
of crystals, and enormous effort has been expended
to understand this role, but many questions remain open.
For example, the nature of glassy systems remains poorly defined.
In systems with competing interactions at different length scales,
complex patterns including stripes and clumps can form. Such phenomena
occur in systems as diverse as electrons in copper oxide planes to
patterns on a zebra.
Dislocations fall into this class of systems;
due to the dipolar nature of the interactions, the dislocations
are repelled from each other at long range, but are attracted at short
range to form grain boundaries.
Thus a better understanding of the organization of dislocations into boundaries
also addresses this larger question of pattern formation.
Computer simulations have made detailed
studies of dynamical processes possible in these systems.
To better analyze and understand these systems,
novel, local probes are needed, which fully take advantage of the
capabilities of the computers being used to generate the data.
Illustrated above is the dislocation density as a function of distance
from the interface over time.
Collaborators include
T.C. Germann, B.L. Holian, J.E. Hammerberg, and M. Mineev.