Predicting the Lifetime of Polymer Pipes in Corrosive Environments

低成本聚合物越来越多地用于民用基础设施应用，例如用于水和天然气输送的管道、波纹排水管、卫生管道和土工膜。 在这些应用中，机械载荷和环境条件的组合可加速聚合物的降解并导致称为应力腐蚀开裂（SCC）的裂纹形成和扩展。SCC的主要特征是多个小裂纹的演化，当其中一个裂纹扩展时最终发生失效。由于聚合物材料的机械和传输性能的随机性，聚合物组分的寿命可能会发生显著变化。 在该项目中，将开发一个数值模型，将断裂行为与液体环境的扩散和随后的聚合物降解相结合。 将进行一系列实验，其中聚合物的机械性能表征为聚合物降解的函数。 这些性质的统计变化是预测聚合物寿命变化的基石。 这项研究将促进我们对聚合物中概率SCC的理解。 此外，它将为工程师提供一种科学的方法来设计聚合物管道，以应对规定的故障风险，这将提高用于民用基础设施应用的管道的结构可靠性。 教育计划包括针对不同专业水平的一系列成员的活动：利用基于网络的管道设计工具的高中夏令营，聚合物行业专业人员的网络研讨会，以及本科生和研究生的大学课程。 与主要基于确定性框架的聚合物组分设计的现有方法相比，本研究由概率框架锚定。 通过包括各种材料特性中的不确定性的影响（即， 机械性能、化学扩散率和分子量），该模型可以捕获聚合物在腐蚀环境中的总体随机响应。本文的研究将得到以下重要成果：1）建立了一个表征聚合物应力腐蚀开裂过程中化学扩散、化学诱导材料降解和裂纹扩展之间相互作用的随机化学-力学模型; 2）建立了一种定量分析力学性能降解与分子量之间关系的方法和实验数据; 3）通过腐蚀性液体环境中裂纹扩展的实验研究进行模型验证;以及4）聚合物管道的基于可靠性的设计方法，该方法将允许工程师以可容忍的故障风险设计具有期望寿命的管道。

Low cost polymers are increasingly used for civil infrastructure applications such as pipes for water and natural gas delivery, corrugated drainage pipes, sanitation pipes, and geomembranes. In these applications, the combination of mechanical loading and environmental conditions can accelerate degradation of the polymer and lead to crack formation and propagation referred to as stress corrosion cracking (SCC). The main feature of SCC is the evolution of multiple small cracks with failure ultimately occurring when one of these cracks propagates. The lifetime of polymer components can vary significantly due to the randomness of mechanical and transport properties of polymer materials. In this project, a numerical model will be developed that combines the fracture behavior with the diffusion of the liquid environment and subsequent degradation of the polymer. A series of experiments will be performed in which the mechanical properties of the polymer are characterized as a function of polymer degradation. The statistical variation in these properties is the cornerstone for predicting the variability in polymer lifetime. This research will advance our understanding of probabilistic SCC in polymers. In addition, it will provide engineers a scientific method to design polymer pipes for a prescribed failure risk, which will improve the structural reliability of pipes used for civil infrastructure applications. The educational plan includes activities targeted for a range of constituents at various levels of expertise: a high school camp that utilizes a web-based tool for pipe design, webinars for polymer industry professionals, and university courses for undergraduates and graduate students. As compared to existing approaches for design of polymer components, which are primarily based on a deterministic framework, this research is anchored by a probabilistic framework. By including the effects of uncertainties in various material properties (i.e., mechanical properties, chemical diffusivity and molecular weight), the model can capture the overall stochastic response of polymers in a corrosive environment. This research will lead to the following important results: 1) a stochastic chemo-mechanical model for SCC in polymers that characterizes the interactions between the chemical diffusion process, chemical-induced material degradation and crack propagation; 2) a methodology and experimental data to quantify the relationship between degradation of mechanical properties and molecular weight; 3) model validation through an experimental study of crack growth in a corrosive liquid environment; and 4) a reliability-based design method for polymer pipes, which will allow engineers to design pipes for a desirable lifetime at a tolerable failure risk.