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

应力腐蚀开裂（SCC）是材料的一种退化现象。易受影响的材料在拉伸载荷（拉式载荷）和腐蚀性环境（如盐溶液）下可能发生SCC。SCC对飞机、桥梁和管道的灾难性故障负有责任，造成了重大的经济损失和人员伤亡。因此，详细研究和了解SCC对于防止桥梁和管道等结构的失效至关重要。在本项目中，通过采用研究随时间变化的塑性变形（蠕变）的方法，提出了一种新的、简单的研究SCC的方法。通过稳定地拉动一个形状像狗骨头的样本，这项研究旨在了解裂缝是如何开始、扩散并最终导致断裂的。在SCC实验过程中，测试每隔一定时间中断一次，利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，特别是在第二阶段（观察到的三个SCC变形阶段之一），这最终促使只在第二阶段进行SCC试验，以预测SCC机制和破裂。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。项目中提出的若干研究活动与教育和外联活动很好地结合在一起。对学生的培训、关于SCC的新课程、SCC研讨会，以及让K-12学生、教育工作者和公众了解SCC现象的外展活动，是研究和教育结合的几个直接成果，使广泛的利益相关者受益，重点关注社会服务不足的群体。技术概述：更好、更安全的材料对于提高生产力、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）过程中的变形过程有助于更好地设计金属材料。虽然对SCC的理解已经扩大，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，限制了力学测试的机理见解。此外，在适应实验室测试结果的方法上存在缺陷，通常是从加速条件到实际服务场景。提出的工作旨在开发新的测试方法，以更好地理解结构的机制，并预测结构的长期寿命，从而实现更安全、更坚固的承重设计，具有更高的抗SCC能力。SCC现象的研究遵循了理解金属材料蠕变行为的概念和程序。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的测试数据，这种创新方法有助于提高对SCC机制的理解（例如，裂纹的起裂和扩展机制）。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熟练掌握SCC相关实验技能的机会。新的SCC课程包括理论和实践活动，使学生具备解决SCC相关问题所需的理论和实践知识。此外，夏季SCC研讨会汇集了学生、工程师、科学家和研究人员，分享和学习SCC领域的最新进展。此外，展示腐蚀、SCC和预防措施影响的外展活动显著地惠及了代表性不足的学生和社区。该项目由金属和金属纳米结构计划（MMN）和促进竞争性研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，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.