Nonlinear Viscoelastic Behavior of Glassy Polymers: Discriminating Experiments and Constitutive Modeling

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Polymers and polymer composites are important engineering materials used in a myriad of industrial and consumer devices, ranging from DVDs to food packaging to automotive components to encapsulants for electronic circuits to matrix resins in aerospace composites. In these applications the polymer can experience significant mechanical loads, where long term mechanical performance is critical. In this research a new class of models will be more fully developed that acknowledge the microscopic structure of polymer glasses, providing engineers with better predictive tools for describing mechanical responses of polymer glasses. A fundamental understanding of the behavior of glassy materials is one of the outstanding problems in condensed matter physics, where dynamic heterogeneity is emerging as a critical organizing idea for the glassy state of matter. A Stochastic Constitutive Model has been developed, where for first time dynamic heterogeneity is explicitly acknowledged. The primary focus of this research is to fully understand the implications and value of explicitly incorporating nanoscale fluctuations associated with dynamic heterogeneity in a constitutive description of polymer glasses. The Stochastic Constitutive Model introduces a new perspective, where the shape of the relaxation spectra changes during the complex thermal-deformation history that a polymer experiences during its life. A major research deficiency in the mechanics of glassy polymers is comprehensive data set of the nonlinear viscoelastic data for a non-commercial material that can be readily produced by all research groups. A second objective of this research is to develop a comprehensive data set of the nonlinear, time dependent mechanical properties for a well characterized, glass forming amine cured epoxy resin.