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

聚合物和聚合物复合材料是用于无数工业和消费设备的重要工程材料，从dvd到食品包装，从汽车部件到电子电路的密封剂，再到航空航天复合材料中的基质树脂。在这些应用中，聚合物可以承受巨大的机械载荷，其中长期机械性能至关重要。在这项研究中，一类新的模型将更充分地认识到聚合物玻璃的微观结构，为工程师提供更好的预测工具来描述聚合物玻璃的力学响应。对玻璃材料行为的基本理解是凝聚态物理学中突出的问题之一，其中动态非均质性正在成为物质玻璃态的关键组织思想。建立了随机本构模型，其中首次明确承认了动态异质性。本研究的主要重点是充分理解在聚合物玻璃的本构描述中明确纳入与动态非均质性相关的纳米尺度波动的含义和价值。随机本构模型引入了一个新的视角，其中弛豫谱的形状在聚合物在其生命周期中经历的复杂热变形历史中发生变化。玻璃聚合物力学研究的一个主要缺陷是所有研究小组都能轻易地制作出非商业材料的非线性粘弹性数据集。本研究的第二个目标是为一种表征良好的玻璃化胺固化环氧树脂开发一套非线性的、随时间变化的机械性能的综合数据集。

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.