CSAR Seminar
SPEAKER: Liang Zhang, University of Iowa
TITLE:
An Atomic Level Material Stability Theory — Failure Analysis
of Nanostructures
DATE: Wednesday, July 26, 2006
TIME: 12:00 Noon
PLACE: 2240 DCL
1304 W. Springfield Ave., Urbana, IL
ABSTRACT
Local elastic instability of crystal lattices is a source of defect
nucleation and material failure. The stability analysis of an
initially pristine lattice is a well-developed subject, on which many
approaches and results have been reported. However, there is no unified
approach for detecting the local instability in a non-homogeneous
atomic system. In this paper, we develop an atomic level material
stability theory which is the atomic counterpart of the material
stability theory in continuum elasticity for atomic structures. We
define the atomic acoustic tensor as an indicator in the stability
criterion to detect material failure at the atomic level. The atomic
material stability criterion is based directly on the atomic energetic
response, in particular the non-convexity of which is the counterpart
of the non-elliptic constitutive behavior in continuum elasticity. The
theory does not resort to continuum homogenization and does not require
the lattice to be pristine. Thus, we expect it to be applicable in
defective nanoscale structures provided that the atomic energy can be
reasonably defined. In addition, the criterion can be easily
implemented in the framework of molecular dynamics/mechanics. To test
for validity, we have applied this stability theory to defective simple
crystals and found that the atomic acoustic tensor can be used to
characterize the instability modes of the defective region. We have
also performed local instability analysis on the initially defective
carbon nanotubes. The tensile limits predicted by this theory are in
good agreement with those reported in the literature.