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

NON-TECHNICAL SUMMARY

Stress 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 SUMMARY

Better 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.