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，如供水和天然气输送管道、波纹排水管道、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会加速聚合物的降解，并导致裂纹的形成和扩展，称为应力腐蚀破裂(SCC)。应力腐蚀开裂的主要特征是多个小裂纹的演化，当其中一个裂纹扩展时，最终会发生破坏。由于聚合物材料的机械和传输特性的随机性，聚合物组件的寿命可能会有很大差异。在这个项目中，将开发一个将断裂行为与液体环境的扩散和聚合物随后的降解相结合的数值模型。将进行一系列实验，其中聚合物的力学性能被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。这一研究将促进我们对聚合物中概率应力腐蚀开裂的理解。此外，它还将为工程师提供在规定的失效风险下设计聚合物管道的科学方法，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：利用基于网络的工具进行管道设计的高中夏令营，面向聚合物行业专业人员的在线研讨会，以及面向本科生和研究生的大学课程。与现有的聚合物组分设计方法主要基于确定性框架相比，这项研究是以概率框架为基础的。通过考虑各种材料性质(即力学性能、化学扩散系数和分子质量)中的不确定性的影响，该模型可以捕捉腐蚀环境中聚合物的总体随机响应。这项研究将产生以下重要结果：1)描述聚合物中SCC的随机化学-力学模型，描述化学扩散过程、化学诱导的材料降解和裂纹扩展之间的相互作用；2)量化力学性能退化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对模型进行验证；以及4)基于可靠性的聚合物管道设计方法，使工程师能够在可容忍的失效风险下设计管道。

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.