Effect of Inhomogeneous Deformation on the Response of Shape Memory Alloy Structures

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Shape memory alloys (SMA) like NiTi are increasingly being used in a range of applications including damping and energy absorption, biomedical devices, MEMS, morphing of structures, etc. The goal of this project is to study the role of localized deformations associated with stress induced phase transformation in SMAs on the response of such structures. Modeling the response of these structures to bending, torsion and tension/compression loadings requires material models capable of capturing differences between tension and compression, multiaxial loadings and the potential for localized inhomogeneous deformations. Although some aspects of SMA behavior can be captured by modern constitutive models, localized deformation is not. A combination of experiment and analysis will be used to bridge this gap. Experiments on simple SMA structures like bending of tubes, axial crushing of shells, and lateral crushing of clusters of tubes will be used to illustrate how localized deformations alter the structural response. To support the modeling of such nonlinearities a material characterization effort will be undertaken in parallel to form the basis of adding the missing features to constitutive models. This involves measuring the material behavior under tension, compression and biaxial loading histories at different temperatures and rates. The results will form the basis for calibrating a multi-scale modeling effort to include the missing features in robust three-dimensional constitutive models. The models will in turn be tested by implementing them in finite element models to simulate the structural experiments.The project involves a collaboration between an experimentalist expert on material and structural instabilities and a theorist expert on modeling of smart materials. The cooperation will generate broadly trained researchers who can become future leaders in multidisciplinary research in academia and industry. Undergraduate participation in the project is used to attract them to graduate school. Laboratory demonstrations to high-school pupils including a significant Hispanic representation are used to expand their interest in engineering and science.