Material Science Seminar

From Electrons To Finite Elements: A Concurrent Multiscale Approach For Metalsby
Gang LuDepartment of Physics, California State University, Northridge, CA 91330-8268In this talk, I will discuss how multiscale modeling can be applied to study (1) Hydrogen
enhanced local plasticity in Al, which is crucial to understanding of H embrittlement of
metals. The atomic and electronic mechanism for enhanced dislocation mobility is
explored; (2) Ductile fracture in Al under mode I loading. The atomistic mechanisms of
dislocation nucleation from the crack tip, and crack propagation are investigated. The
electronic states at the crack tip during the fracture process are examined in detail.
Multiscale modeling of material properties has emerged as one of the grand challenges in
materials science and engineering. Multiscale modeling is necessary because the
macroscopic properties of materials are largely determined by the microscopic processes,
taken place particularly at lattice defects. A typical example is the mechanical response of
metals to external loads, which is characterized as ductile or brittle at the macroscopic
scale, depending on the ability of the material to absorb the load by plastic deformations.
This response can be drastically altered by the presence of impurities and their influence
on bonding between the atoms in crucial regions like the crack tip and dislocation core.
The delocalized nature of electronic states in a metal makes the description of such
effects particularly challenging. We have recently developed a multiscale modeling
approach that concurrently couples quantum mechanical calculations for electrons, to
empirical atomistic simulations for classical atoms, and to continuum mechanical
modeling for finite elements, in a unified description [1]. In specific, the electronic
structure calculations are performed with the plane-wave pseudopotential method based
on the density-functional theory (DFT), the classical atomistic simulations with the
embedded-atom method (EAM), and the continuum modeling with the Cauchy-Born rule
in the local Quasicontinuum (QC) formulation [2]. The multiscale method is
implemented in the context of the QC framework with the additional capability to include
DFT calculations for a selection of non-local QC atoms. A novel coupling scheme has
been developed to combine the DFT and EAM calculations [3] in a seamless fashion to
deal with non-local QC atoms.
Reference:
[1] G. Lu, E.B. Tadmor, and E. Kaxiras, Phys. Rev. B 73, 024108 (2006).
[2] E.B. Tadmor, M. Ortiz, and R. Phillips, Philos. Mag. A 73, 1529 (1996).
[3] N. Choly, G. Lu, W. E and E. Kaxiras, Phys. Rev. B 71, 094101 (2005).Refreshments served at 2:15All MASC first-year students are required to attend

Location: John Stauffer Science Lecture Hall (SLH) - 102

Audiences: Everyone Is Invited

Contact: Petra Pearce