Physics Colloquium
Friday, Sept. 14th, 2007,
4:00 P.M.
E300 Math/Science
Center; Refreshments at 3:30 P.M. in
Room E200
Michael Falk
Materials Science and Engineering
University of Michigan
The statistical mechanics of shear banding in metallic glasses
Metallic glasses represent a promising high strength
material, but their use is limited by the onset of a
shear banding instability when their material
strength is exceeded. Recent simulation studies of
the initiation and development of localized
deformation in molecular dynamics simulations of a
number of amorphous systems reveal the structural
changes that accompany plastic deformation and
localization involve a decrease in the local short
range ordering. We have simulated both
two-dimensional and three-dimensional systems in
nanoindentation [1], uniaxial tension [2] and
compression [3] in plane strain. The degree of
strain localization depends sensitively on the
quench rate during sample preparation, with
localization only arising in more gradually quenched
samples. A systematic analysis of simulated systems
in simple shear geometries [4] reveals that a
Boltzmann-like relationship between strain rate and
structure holds over large variations in both the
applied strain rate and the initial structural state
of the glass. Scaling is observed over eight orders
of magnitude in strain rate. The consequences of
this scaling for constitutive models of glass
plasticity will be discussed.
[1] Y. Shi and M.L. Falk, Structural transformation
and localization during simulated nanoindentation of
a non-crystalline metal film, Applied Physics
Letters, Vol. 86, pp. 011914 (2005).
[2] Y. Shi and M.L. Falk, Strain localization and
percolation of stable structure in amorphous solids,
Physical Review Letters, Vol. 95, pp. 095502 (2005).
[3] Y. Shi and M.L. Falk, Atomic-scale simulations
of strain localization in three-dimensional model
amorphous solids, Physical Review B, Vol. 73, pp.
214201 (2006).
[4] Y. Shi, M.B. Katz, H. Li and M.L. Falk,
Evaluation of the disorder temperature and free
volume formalisms via simulations of shear banding
in amorphous solids, Physical Review Letters, Vol.
98, 185505 (2007).
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