CAREER: Elucidating the fundamental mechanisms of stress corrosion cracking from smooth tensile specimens under constant load for quantitative life-prediction

非技术总结应力腐蚀开裂（SCC）是一种材料退化现象。敏感材料在拉伸载荷（拉式载荷）和腐蚀性环境（如盐溶液）的存在下可能发生SCC。SCC对飞机、桥梁和管道的灾难性故障负责，导致重大经济损失和人员伤亡。因此，详细研究和了解SCC以防止桥梁和管道等结构的失效至关重要。在本计画中，借由研究随时间变化的塑性变形（蠕变）的方法，提出一种新且简单的方法来研究应力腐蚀开裂。通过稳定地拉动形状像狗骨头的样品，该研究旨在了解裂缝如何开始，蔓延，并最终导致断裂。在SCC实验过程中，测试会定期中断，以便使用先进的显微镜在微观尺度（微观结构）上捕捉结构的演变。SCC试验数据和微观结构是相关的，特别是在第二政权（观察到的SCC变形的三个阶段之一），这最终促进进行SCC试验只有到第二政权预测的SCC机制和断裂。这种新方法还有助于根据实验室的短期实验预测材料在长期内的行为。该项目中提议的若干研究活动与教育和外联活动很好地结合在一起。学生培训，SCC的新课程，SCC研讨会，以及让K-12学生，教育工作者和公众接触SCC现象的外联活动是研究和教育整合的一些直接结果，使广泛的利益相关者受益，重点关注社会服务不足的问题。更好、更安全的材料对于提高生产率、安全性和国家安全至关重要的先进工程结构至关重要。更好地理解应力腐蚀开裂（SCC）过程中的变形过程，可以更好地设计金属材料。虽然对SCC的理解已经扩展，但它仍然基于经验数据; SCC的测试是缓慢的，有时会忽略早期裂纹阶段，限制了机械测试的机械见解。此外，调整实验室测试结果的方法存在缺陷，通常是从加速条件到实际服务场景。拟议的工作旨在开发新的测试方法，以更好地理解和预测遭受SCC的结构的长期寿命，从而实现更安全，更坚固的承载设计，具有更高的抗SCC能力。应力腐蚀开裂现象的研究是根据为理解金属材料的蠕变变形行为而开发的概念和程序进行的。通过分析在电化学环境中承受恒定载荷的简单光滑狗骨形拉伸试样获得的测试数据，这种创新方法可以帮助提高对SCC机制（例如，裂纹萌生和扩展机制）的理解。它还允许确定断裂时间、变形速率和各种其他参数。拟议的研究与教育和外联活动很好地结合在一起。该项目为研究生和本科生提供了机会，使他们能够熟练掌握与SCC相关的实验技能。新的SCC课程涉及理论和实践活动，使学生具备必要的理论和实践知识，以解决SCC相关问题。此外，SCC夏季研讨会将学生，工程师，科学家和研究人员聚集在一起，分享和了解SCC领域的最新进展。此外，宣传活动，以展示腐蚀的影响，SCC，该项目由金属和金属纳米结构计划（MMN）和刺激竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYStress corrosion cracking (SCC) is a type of material degradation phenomenon. A susceptible material can undergo SCC in the presence of a tensile load (pull type loading) and a corrosive environment such as a salt solution. SCC has been responsible for catastrophic failures in aircraft, bridges, and pipelines, resulting in significant economic losses and casualties. Therefore, it is crucial to study and understand SCC in detail to prevent failures in structures like bridges and pipelines. In this project, a new and simple method to study SCC is suggested by adapting methods used to study time dependent plastic deformation (creep). By steadily pulling on a sample shaped like a dog bone, the study aims to understand how cracks start, spread, and finally cause a break. During SCC experiments, the test is interrupted at regular intervals to capture the evolution of the structure at a microscopic scale (microstructure) using advanced microscopes. The SCC test data and microstructure are correlated, particularly in the secondary regime (one of three stages of SCC deformation observed), which eventually promote conducting SCC tests only up to the secondary regime to predict the SCC mechanism and fracture. This new method also helps predict how materials behave over a long period based on short-term experiments in the lab. Several research activities proposed in the project are well integrated with educational and outreach activities. Training of students, a new course on SCC, a workshop on SCC, and outreach activities to expose K-12 students, educators, and the public to the SCC phenomenon are a few direct outcomes of the integration of research and education, benefitting a wide spectrum of stakeholders with a focus on society’s underserved. TECHNICAL SUMMARYBetter and safer materials are critical to advanced engineering structures essential in increasing productivity, safety, and national security. A better understanding of deformation processes during stress corrosion cracking (SCC) leads to better design of metallic materials. While the understanding of SCC has expanded, it remains based on empirical data; testing for SCC is slow and sometimes overlooks early crack stages, limiting mechanistic insights from mechanical tests. Moreover, there is a deficiency in methods to adapt lab test outcomes, often from accelerated conditions to actual service scenarios. The proposed work aims to develop novel test methods to have a better mechanistic understanding and predict long-term life for structures undergoing SCC, leading to safer and robust load-bearing designs with higher resistance to SCC. The SCC phenomenon is being studied following the concepts and procedures developed to understand creep deformation behavior of metallic materials. By analyzing test data obtained from simple smooth dog-bone-shaped tensile specimens subjected to constant loads in an electrochemical environment, this innovative approach can help improve understanding of the mechanisms of SCC (for example, crack initiation and propagation mechanisms). It also allows for the determination of fracture time, deformation rate, and various other parameters. The proposed research is well integrated with educational and outreach activities. The project provides opportunities for graduate and undergraduate students to become proficient in experimental skills related to SCC. The new course on SCC involving theory and hands-on activities equips students with the necessary theoretical and practical knowledge to solve SCC-related problems. Moreover, the summer workshop on SCC brings together students, engineers, scientists, and researchers to share and learn about the latest advancements in the field of SCC. Additionally, outreach activities to showcase the effects of corrosion, SCC, and prevention measures significantly benefit students and communities from underrepresented populations.This project is jointly funded by the Metals and Metallic Nanostructures Program (MMN) and the Established Program to Stimulate Competitive Research (EPSCoR).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.