Multi-Physics of Elastomer Aging: Macrostructure Mechanical Properties based on Morphological Chemical Degenerations

通常称为橡胶的弹性体具有广泛的应用，可用作轴承、密封胶、轮胎和防振支座。在这样的操作下，除了循环机械载荷外，弹性体还暴露在氧气和高温下。氧气和温度会严重降低材料的性能。这种降解被称为老化，并导致表面脆化、收缩和恶化。老化过程，加上机械载荷，加剧了弹性体中的裂纹扩展，降低了它们的使用性能。衰老的实验测试必然是一个耗时的过程。拥有一个可用于模拟的理论框架将极大地加速开发具有更广泛应用范围的新的、令人兴奋的、可靠的材料。这项工作将阐明在机械载荷和老化的共同作用下，弹性体的力学响应如何随其寿命的变化而变化。这项研究将促进人们对降解对弹性体耐久性影响的科学认识。该项目的开发周期由实验工作组成，然后是建模、仿真，再回到实验验证。这种结合的方法是科学方法的理想例证，将用于通过大学项目接触K-12和少数族裔学生。这项研究还将在这一跨学科领域培养一批不同的本科生和研究生，形成美国弹性体行业在全球竞争中至关重要的下一代科学家。为了描述在热-化学-机械老化过程中弹性体的变形响应和失效机制的演变，本项目概述了一系列相互关联的化学、形态和力学变化的实验、理论和数值研究。在第一阶段的工作中，弹性体宏观结构力学性能的恶化将在实验上与其形态变化(如交联键的断裂/形成和键的转变)联系在一起。该项目的第二阶段将开发一种数学上可验证的程序，将化学实验中获得的储存和耗散的能量纳入热力学形式。在第三阶段，该项目试图了解异质老化降解对弹性体力学响应的影响。本构方程的数值模拟将被用来对照进一步的实验研究来验证该模型。有待获得的知识和有待开发的理论框架将导致高度耦合的基于物理的模型，这些模型映射出弹性体的宏观结构行为和失效机制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Elastomers, often commonly referred to as rubbers, have a wide range of applications as bearings, sealants, tires, and anti-vibration mountings. Under such operation, elastomers are exposed to oxygen and elevated temperature, in addition to cyclic mechanical loading. Oxygen and temperature heavily degrade the materials' properties. This degradation is known as aging and induces brittle, shrunken, and aggravated surfaces. The aging process, coupled with mechanical loading, intensifies crack propagation in elastomers and reduces their serviceability. Experimental testing of aging is, necessarily, a time-consuming process. Having a theoretical framework that can be used for simulations will tremendously speed up the development of new, exciting, and reliable materials with a broader range of applications. This work will elucidate how the mechanical response of elastomers changes over their lifetime under the coupled effects of mechanical loading and aging. This research will advance the scientific knowledge of degradation effects on durability of elastomers. The development cycle of the project consists of experimental work, followed by modeling, simulation, and back to experimental verification. This combined approach, which is an ideal illustration of the scientific method, will be used for outreach to K-12 and minority students through university programs. This research will also train a diverse group of undergraduate and graduate students in this interdisciplinary field, forming the next generation of scientists that the U.S. elastomer industry critically needs to compete globally. To characterize the evolution of the deformation response and failure mechanism of elastomers under thermo-chemo-mechanical aging processes, this project outlines a series of interconnected experimental, theoretical, and numerical studies of the chemical, morphological, and mechanical changes. In the first stage of work, the aggravation of macrostructural mechanical properties of elastomers will be experimentally linked to their morphological changes (such as cross-link breakage/formation, and transformation of linkages). The second stage of the project will develop a mathematically verifiable procedure for incorporating stored and dissipated energies - obtained in chemical experiments - into the thermodynamic formalism. In the third stage, the project seeks to understand the effects of heterogeneous aging degradation on the mechanical response of elastomers. Numerical simulations of the constitutive equations will be used to verify the model against further experimental studies. The to-be-obtained knowledge and to-be-developed theoretical framework will lead to highly coupled physics-based models which map the elastomers' macrostructural behavior and failure mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.