Ph.D. Dissertation Defense by Douglas E. Spearot
Tuesday, July 12, 2005
(Dr. David McDowell, Chair)
" Atomistic Calculations of Nanoscale Interface Behavior in FCC Metals"
This dissertation focuses on the behavior of homogeneous FCC metallic interfaces on the nanoscale. Specifically, atomistic calculations (molecular statics and molecular dynamics) with embedded-atom method potentials are used to study the fundamental failure processes that occur at a bicrystal interface in Cu and Al as a result of a mechanical deformation. There are four primary objectives to this dissertation. First, molecular statics calculations are used to determine the most appropriate (minimum energy) structure of homogeneous bicrystal interfaces in Cu and Al. Interface structures and energies are reported in this work, with comparison to both theoretical and experimental characterizations of interface configuration. Second, molecular dynamics simulations are performed to provide a characterization of atomic scale inelastic behavior, including both dislocation and void nucleation activities which lead to interfacial failure. Specifically, two ‘types' of interfaces are highlighted in this work: a mirror symmetric interface in aluminum and an asymmetrically dissociated interface in copper. Distorted interface structures (after the dislocation nucleation event) are discussed in terms of partial dislocations or disclinations. Third, molecular dynamics simulations are used to investigate potential relationships between interface structure and interface properties or morphology. The orientation of the primary slip planes with respect to the loading direction and the porosity within the interface region are found to be critical factors in defining the strength of the bicrystal interface, for example. Finally, results of the atomistic calculations are utilized to motivate improved forms for continuum interface separation potentials, ultimately increasing the applicability of these relationships to include cohesive failure in ductile crystalline materials.