Ph.D. Proposal Presentation by James E. Shepherd
Wednesday, May 4, 2005

(Dr. David L. McDowell, Chair)

"Evolution And Effect of Nanoscale Structure on the Mechanical Behavior of Polymers by Means of Hierarchical Atomistic and Continuum Modeling"


The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures such as entanglements, crystallites, and molecular orientation. These nano-scale structures evolve during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations of the nano-scale structures. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. An internal state variable continuum model has been developed whose state variables and evolution equations are related to the nano-scale structures. In this research, separate atomistic models and methods will be developed to investigate the primary nano-scale structures that affect mechanical behavior: the evolution of entanglements, crystallization, and other molecular interactions during thermo-mechanical deformations. The results of these simulations will be used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the model's material parameters. The end result will be a continuum model that reflects the atomistic structure of the polymer. Ideally, the methods employed will be general enough to be applicable to most types of polymer systems .