Seminar: Visiting Scholar, James T. Burns, Ph.D.
September 9, 2016
“The Effect of Environment on the Structural Integrity Management of Fatigue in Airframe Aluminum,” by University of Virginia assistant professor in materials science and engineering, James. T. Burns, will be held on Thursday, September 15, 2016, at 11:00 a.m. in the MEK Green Classroom (3550).
Metal-environment interactions influence the fatigue behavior of the aerospace Al alloy 7075-T651 via (1) enhanced mechanical driving force for crack formation localized about pre-existing ground-based corrosion topography, and (2) local chemical/electro-chemical processes concurrent with cyclic plastic damage accumulation at both crack formation sites and the growing crack tip. Such environmental effects should be incorporated into next generation structural integrity management techniques to increase accuracy and reduce over-conservatism.
High fidelity quantitative and qualitative characterization of the crack formation process established the primary influence of corrosion micro-topography (5-20 µm) and underlying constituents on the local strain concentration that governs fatigue formation. Additionally, load induced surface markers enabled characterization of the cracking front progression proximate to the nucleating corrosion features (between 1-500 µm); various small crack relationships were applied to the data, but simple elastic stress intensity range best correlated the data.
Crack front undulations were observed due to localized interactions with microstructure features; corresponding 150% variability in growth rate was observed and statistically described. Fatigue testing was performed at 23°C (RH>90%) as well as low temperature (-50°C and -90°C) environments typical of high altitude airframe operation; the temperature reduction resulted in an order of magnitude increase in the crack formation life and reduction in crack growth kinetics.
This unique and extensive database was used to validate engineering-level “stress/strain life” predictions of crack formation life and fracture mechanics-based modeling of small crack progression; the application of these concepts are discussed in the context of airframe structural integrity management.
Dr James T. Burns has been an assistant professor in the Center for Electrochemical Science and Engineering within the Department of Materials Science and Engineering at the University of Virginia since 2011. Burns received a B.S degree from the United States Air Force Academy in Engineering Mechanics with a Mathematics minor in 2002. He completed his M.S. and Ph.D degrees in Material Science and Engineering at the University of Virginia in 2006 and 2010, respectively.
After his commission, he served as an Aircraft Battle Damage Engineer and Assistant Aircraft Structural Integrity Program (ASIP) manager for the C-130 from 2002-2004, and he served as a Research Engineer at the Air Force Research Laboratory from 2006-2010. During his military service he received unit level recognition as the top Company Grade Officer, led the top Engineering Team, was an Outstanding Performer in Operation Readiness Inspections, and received the US Air Force Commendation Medal in 2009.
Burns has received an AFOSR Young Investigator award and the Virginia Space Grant Consortium New Investigator Program Award. Professor Burns’ research focuses on the intersection of metallurgy, solid mechanics and chemistry, which is currently at the forefront of several important engineering challenges.