SGER: Investigation of Auxetic Metals

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PI: Alison FlatauInstitution: University of MarylandTitle: Investigation of auxetic metalsAbstract:This SGER research project entails an investigation of metals that exhibit auxetic or negative Poisson's ratio behavior and a feasibility study into engineering applications that use this effect. An auxetic material is one that increases in its lateral dimension in response to stretching or tensile loading. This novel and counterintuitive behavior has been used to advantage in a variety of composite structural systems, cellular foams, and polymers. However, metals that exhibit auxetic properties are rare and require careful orientation of a structural member relative to the molecular crystal lattice orientation for observation of this effect. This research effort will include analysis and measurement of mechanical properties such as elastic modulus and Poisson's ratio in single crystal and textured polycrystal metals, with a particular focus iron-aluminum alloys (Alfenol) and on a relatively new material, the iron-gallium alloy known as Galfenol. Preliminary predictions of Poisson's ratio's for Alfenol and Galfenol in a [110] orientation indicate respectively that values of as low as -0.44 and -0.75 can be realized. The study will investigate these materials and develop finite element models for use in identifying compositions of auxetic metals with properties best suited for the design and development of fasteners that function because of friction induced under tensile loading due to transverse expansion resulting from the auxetic nature of the material. The proposed research offers the potential for a broad commercial impact if successful, as the fastener application suggested offers an affordable alternative to nut-and-bolt methods for joining structural members. If effective as a single component fastener, there should be many uses in which two-component nut-and-bolt connectors might be replaced, especially in space applications and in microsystem applications, where there are inherent difficulties in manipulation of the nut to secure a bolt. Additionally, the principal investigator has a strong track record for engaging underrepresented undergraduate students in laboratory research experiences both during the academic year and summers, and will offer research opportunities for both women and minorities students throughout the course of this project.