(Drs. David McDowell and Karl Jacob, co-advisors)
"Interface Cohesion Relations Based on Molecular Dynamics Simulations"
Using molecular dynamics simulations based on embedded-atom method (EAM) potentials (Daw and Baskes, 1983; 1984), a methodology is presented to develop continuum cohesive interface separation constitutive laws over various length scales. These laws differ from existing continuum models in that discrete atomistics are used to incorporate effects of atomic structure at the interface, including imperfections. The EAM supplies the functions necessary to describe the energy associated with the electrostatic force between adjacent atoms as well as the energy required to embed an atom within the electron field distribution of a crystalline lattice. Atomistic calculations are used to explicitly characterize some of the first-order relevant length scale effects on interfacial separation. Specifically, ratios between specimen width, depth, height and interface radius of curvature, relative to the equilibrium interatomic spacing, are shown to effect the peak stress and displacement associated with peak stress. Internal state variable (ISV) theory is used to incorporate nanoscale effects, similar to those studied with the atomistic simulations, into a constitutive law to characterize the structure and evolution of an interface. Additionally, investigations of path-history dependence and interface damage are performed for use in the continuum separation law. Two atomic geometries are studied in this preliminary investigation, beginning with a planar copper interface with 45-degree angle misorientation between lattices and then examining the effect of interface curvature on the same lattice misorientation structure.