CAREER: Understanding Micromechanisms of Fatigue in Shape Memory Alloys

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The research objective of this Faculty Early Career Development (CAREER) Program award is to investigate the fundamental mechanisms that are responsible for fatigue failure in shape memory alloys (SMAs), with a focus on deformation and phase transformation at the microstructural length scale. Low cycle fatigue, where the SMA undergoes a relatively low number of cycles at high stress amplitudes, and very high cycle fatigue, where the SMA undergoes a very high number of cycles at low stress amplitudes, will be studied. The solid-to-solid phase transformation that enables the unique properties of SMAs will be quantitatively characterized at the grain level, and linked to the mesoscopic response and macroscopic stress-strain behavior of these alloys. The resulting unique, quantitative information on phase transformations will be used to improve the accuracy of lifetime and performance predictions, as well as the optimal design, of these materials. Understanding the links between microstructure and macroscopic behavior is a fundamental challenge in the design and use of materials. SMA components - for example, in military, aerospace, biomedical, and automotive applications - are being increasingly used under fatigue conditions, and a quantitative understanding of the effect of microstructure on their fatigue behavior is critically necessary. This project incorporates a number of educational efforts that are closely tied to the proposed research, including undergraduate summer internships, graduate student enrichment involving a collaborative effort with the Department of Mathematics at the University of Bristol, incorporation of research results into coursework, and dissemination of research findings through a public seminar series and television show.