Understanding the Unique Fatigue Behavior of Magnesium Alloys

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

Most structural components in engineering, particularly those bearing repetitive loading and operating at an elevated temperature, are metals. Magnesium alloys are some of the lightest metals and exhibit the very desirable high strength-to-weight and stiffness-to-weight performance ratios. Moreover, these metals are nontoxic, which also underline their potential for biomedical applications. However, one major obstacle preventing magnesium alloys from a wider use is the limited understanding of their fatigue behavior--material behavior under repeated mechanical loads, which is unique among structural metals due to its complexity. This award supports a fundamental study of the fatigue behavior of magnesium alloys through direct experimental observations. The research will provide basic knowledge of the mechanisms of deformation that lead to failure due to fatigue, and a database of experimental observations to develop and validate material models essential for the engineering design of magnesium-based parts. The effort will promote the engineering science of light-weight, high-efficiency alloys; and advance the national health, prosperity, and welfare; and secure the national defense through cost-efficient applications in the automotive, aerospace, healthcare, and defense industries. The research will be integrated into an education program involving both graduate and undergraduate students to facilitate an understanding of sophisticated scientific concepts in magnesium research. For example, an educational video with interesting experimental visuals and 3D animations will be developed for undergraduate students and public; and self-directed and open-ended projects with relevance to magnesium alloys will be integrated into the existing capstone senior design classes. The characteristic fatigue behavior of magnesium alloys is the result of the existence of twins, twinning-detwinning activities, and their interactions with slips and grain/twin boundaries. The overall objective of this research is to understand how twins and twinning-detwinning activities, respectively, contribute to fatigue damage in magnesium alloys. To achieve this objective, three types of experiments will be designed and conducted: 1) fatigue with no involvement of twins and twinning, 2) fatigue with significant involvement of twinning-detwinning, and 3) fatigue with pre-designed twins without involving twinning-detwinning. These experiments will be realized using a magnesium alloy with a strong texture, and a proper design of the stress state and loading history with respect to the material orientation. Ex-situ experiments together with in-situ experiments using companion specimens will be conducted to facilitate microscopic characterizations. Fatigue microcracking with the influence of twins, twin-twin boundaries, and interactions of twining and grain boundaries will be observed to elucidate the major micromechanisms governing the fatigue processes. The results from the research will form a base to develop mechanism-based fatigue damage models for magnesium alloys and provide information for the design of magnesium alloys with improved fatigue resistance. 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.