Prof. Burns is always interested in working with motivated students. If you are interested in environmental cracking, please check out the projects below for current graduate student openings. If you would like more information or are interested in applying, please contact Prof. Burns at firstname.lastname@example.org with any questions you may have.
Effect of high-altitude (low temperature/water vapor pressure) environments on fatigue crack growth of aerospace Al
Substantial work has been performed to incorporate the effects of mechanical loading spectrum into prognosis modeling of fatigue damage; however similar efforts have not been put forth to understand the strong influence of the environmental spectrum. Fatigue behavior is governed by both mechanical (stress intensity range, ΔK) and chemical driving forces; as such, the loading environment significantly affects the fatigue life of aluminum components. Specifically, loading in a moist-air environment produces atomic hydrogen (H) that enters the material at the crack tip and enhances damage by one or more unique mechanisms. Airframe engineers employ either a fracture mechanics (USAF) or safe-life approach (USN) to manage the effect of fatigue on structural integrity, where the material properties for both are gathered in ambient lab-air environments with relatively high levels of moisture (RH ≈ 20 ‑ 70%). However, in general a significant portion of fatigue loading on both fighter and transport airframes occurs at high-altitude, low-temperature, and low water vapor pressure environments. Critically, research has shown that loading at low temperatures (less than -50°C) reduces crack growth rates (da/dN) to vacuum levels. Incorporating the beneficial effects of the high-altitude environments into current structural integrity management approaches may produce more accurate fatigue modeling, reduce conservatism, and reduce the flight line and depot inspection burden. The objective of this proposed task is to (1) develop a database where temperature, PH2O, and loading parameters vary for legacy (7075-T651) and modern (2199-T8x) aerospace aluminum alloys, (2) gain mechanistic understanding of the environmental fatigue process, and (3) use results from (1) and (2) to inform and support the development of a fracture mechanics based life prediction algorithm for variable environments.