Ph.D. Dissertation Defense by Rémi Dingreville
Monday, February 14, 2005

(Dr. Jianmin Qu, Chair)

"Modeling and Characterization of Mechanical Behavior of Nano-Sized Structural Elements and Nanostructured Materials"

Abstract

Over the past few years, at the intersection of diverse disciplines, the fields of nanostructure science and nanostructured materials have been growing explosively and promise new and novel performances. Steady technological progresses in all fields of nanoscale technology and probe technology have enabled us to synthesize, assemble, develop, characterize and improve nanostructured materials. The lack of understanding of their macroscopic behavior is a major roadblock for inserting these materials into engineering applications. In this proposed research, an innovative approach combining continuum mechanics and atomistic simulation will be conducted to develop a nanomechanics theory for modeling and predicting the macroscopic behavior of nanomaterials.

The research will be comprised of both atomistic simulation and modeling components of analysis. The atomistic simulation portion of this work will consist of evaluating and studying the issue of surface and interface properties and their effects on nanostructured materials. We will perform atomistic simulations using EAM potentials to study various FCC metal surfaces of different orientations and to numerically determine the surface elasticity through molecular statics. The study of surface and interface stress effects on the properties of nanostructural elements such as thin films, nanowires and nanospheres will also be investigated. Similar to the proposed work for surface properties, we will perform atomistic simulations using EAM potentials to study various nanostructural elements and numerically determine their effective properties through molecular statics. The modeling portion of this work will consist of developing models to predict the effective properties of nanostructured materials based on the discrete atomic structure and interaction near interfaces, and relevant mechanical and physical mechanisms involved. A framework will be developed to incorporate the surface details into the continuum theory of mechanics by casting its discrete atomic structure into thermodynamic quantities. Furthermore, in this proposed work, two directions will be explored to model the so-called Hall-Petch “breakdown”. First, micromechanics models will be developed by considering nanostructured materials as composite materials with grain-size dependence plasticity and they will incorporate the interfacial properties concept developed earlier. Second, a framework based on internal state variable (ISV) will also be proposed. A set of internal variables will be considered to account for different deformation mechanisms involved during the plastic flow of nanostructured materials as a second alternative to describe the Hall Petch relationship.

It is anticipated that this research will result in a comprehensive understanding of how molecular structure affects the macroscopic material behavior. In terms of engineering applications, this may prove to be a useful tool for multi-scale modeling of heterogeneous materials with nanometer scale microstructures. The results from this research will provide insights on surface properties for several material systems; these will be very useful in many fields including surface science, tribology, fracture mechanics, adhesion science and engineering, etc. This work will also provide a tool to model and predict the effective properties of nanostructured materials. This will accelerate the insertion of nano-size structural elements, nano-composite and nanocrystalline materials into engineering applications.