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In situ crack tip pH measurements for corrosion fatigue (CF) cracks in sensitized AA5456-H116 loaded under low loading frequencies show that cathodic polarization can arrest actively growing stress corrosion cracking (SCC) and CF cracks and produce a local alkaline crack tip pH. A method for measuring crack tip pH in situ was developed. For AA5456-H116 under a single level of high sensitization, CF experiments while loading in the Paris regime at a loading frequency of 0.1 Hz were conducted under freely corroding conditions and a cathodic polarization of −1.3 VSCE. Results show that under freely corroding conditions the crack actively grows, and the crack tip pH is slightly acidic, while at −1.3 VSCE an alkaline crack tip develops with a pH of 10 to 12. The findings of this study support the earlier published hypothesis that crack arrest of SCC and low loading frequency CF cracks is due to corrosion-induced blunting after the development of highly alkaline conditions that cause corrosion of the crack tip region blunting and halting the crack. 

With large enrollments (about 200-350) of primarily non-majors, engaging students in the required introductory materials science and engineering course at our university has been a longstanding challenge. In moving to the virtual format in the fall of 2020, we significantly adapted several aspects of the course, many of which have continued to the hybrid format in future semesters, with good results. The primary content was provided through asynchronous videos; this format allowed us to break content into digestible pieces. In particular, multiple mini-lectures and example videos were pre-recorded for each week, with a total viewing time per week somewhat less than the typical total class time. To provide real-time, structured interaction, one live virtual class session per week was held, centered on previously submitted student questions. Smaller teaching-assistant-led recitation sections also met live (virtually or in person), during which “clicker” questions were asked through TopHat. Assignments were also updated to take advantage of the virtual format. Multiple small assignments with lower stakes were due throughout the week: a reading/lecture quiz, a survey to submit questions, and a shortened homework assignment. Finally, we changed some content near the end of the course to allow students to connect the course to their own career aspirations, which we expect can aid in longterm retention. Specifically, students chose among several possible topics to cover in the final weeks, covered via typical pre-recorded lectures and reading, and also guest lectures. They wrote an abstract-length reflection on how they could use what they learned in this course later in their careers. Overall, students remained engaged with the course throughout the semester and provided favorable comments and evaluations of the course, including higher numerical evaluations of the course than in prior semesters.