Abstract

In 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 2:15

All MASC first-year students are required to attend