Collaborative Research: Nonlinear Mechanical Spectroscopy of Glassy Polymers to Probe Viscoelastic Constitutive Behavior

该奖项支持研究，以表征玻璃状聚合物的非线性粘弹性行为。了解玻璃态聚合物的长期力学行为对于确保玻璃态聚合物在需要低密度和高比强度材料的应用中（如汽车、体育和航空航天工业）作为独立材料或作为先进复合材料的基体材料使用时的耐久性至关重要。该项目将采取措施，从根本上解决这一挑战，使用一种新的非线性指纹识别方法，有望为开发优质产品带来重要进展，从而使美国工业和社会受益。在过去，指纹识别方法已被用于表征聚合物流体。该奖项通过新颖的实验和适当的非线性本构建模和验证，将该方法扩展到聚合物玻璃。该项目的研究生将接受这项前沿研究的培训，其中涉及时间相关材料的实验和计算力学，玻璃态聚合物物理学以及工程聚合物的结构-性能关系。该项目还将利用德克萨斯理工大学和德克萨斯大学达拉斯分校的STEM外展项目，激发K-12学生对科学和工程的兴趣。该项目将研究与固体聚合物的非线性粘弹性行为相关的基础知识。这就需要一个通用的方案来对各种观察到的行为进行分类，并使用这些观察结果来挑战相关的本构方程。该研究将使用大振幅振荡剪切和机械光谱烧孔指纹识别方法相结合，提供一系列玻璃状聚合物的非线性粘弹性行为的指纹，并挑战他们对一组非线性本构关系的预测从几个领先的模型从文献。这项工作不仅表明该方法可以应用于玻璃状聚合物，而且通过选择检查具有不同程度的非均匀性的聚合物，如通过β-松弛强度估计的，该方法可以区分不同类型的非线性行为，并且原则上确定动态非均匀性的细节如何影响指纹和本构模型参数。这为聚合物非线性力学中的结构-性能关系提供了一个重要的进展。此外，这项工作提供了一个关键的评估指纹范式，目前开发的剪切变形的非线性流体，通过在非体积保持条件下进行测量，即，拉伸和压缩，以形成作为所述变形几何形状的函数的材料指纹，并将它们与剪切结果进行比较。

This award supports research to characterize the nonlinear viscoelastic behavior of glassy polymers. Understanding the long-term mechanical behavior of glassy polymers is critical for assurance of the durability of glassy polymers in their use as stand-alone materials, or as matrix materials for advanced composites, in applications that require low-density and high specific strength materials, such as in automotive, sports, and aerospace industries. This project will take steps to address the challenge from a fundamental perspective using a novel nonlinear fingerprinting methodology that promises to bring important advances for development of premier products, hence benefiting US industry and society. In the past, the fingerprinting methodology has been used to characterize polymeric fluids. This award extends the method to polymer glasses, both through novel experiments and through appropriate nonlinear constitutive modeling and validation. The graduate students on the project will be trained in this cutting edge research, which involves experimental and computational mechanics of time-dependent materials, glassy polymer physics, and structure-property relations for engineering polymers. The project will also leverage STEM outreach programs at both Texas Tech University and University of Texas Dallas to excite K-12 students about science and engineering.Fundamental knowledge related to the nonlinear viscoelastic behavior of solid polymers will be pursued in this project. This requires a general scheme to classify the variety of observed behaviors and use these observations to challenge the relevant constitutive equations. The research will use the combined Large Amplitude Oscillatory Shear and Mechanical Spectral Hole Burning fingerprinting methodology to provide fingerprints of the nonlinear viscoelastic behavior of a series of glassy polymers and to challenge them against a set of nonlinear constitutive law predictions from several leading models from the literature. Not only will the work show that the method can be applied to glassy polymers, but by choosing to examine polymers with different degrees of heterogeneity, as estimated by the strength of the beta-relaxation, the method can differentiate among different types of nonlinear behavior and, in principle, determine how the details of the dynamic heterogeneity impacts the fingerprints and the constitutive model parameters. This provides an important advance in ideas of structure-property relations in the nonlinear mechanics of polymers. Furthermore, the work provides a critical evaluation of the fingerprinting paradigm, currently developed for shearing deformations in nonlinear fluids, by making measurements in non-volume preserving conditions, viz., tension and compression to develop material fingerprints as a function of said deformation geometries and comparing them to the shearing results.