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This paper presents the results of numerical and experimental investigations into the elastic properties of iron-gallium
alloys known as Galfenol, one of only a few metal alloys known to exhibit large auxetic or negative Poisson's ratio
behavior. This research was undertaken to develop an understanding of the molecular mechanisms that lead to the
unusual macro-scale trends in Galfenol elastic properties, as well as to create an experimentally determined database of
these composition-dependent properties. To accomplish this, we have developed quantum theory-based models of the
composition-dependent electronic structure of Galfenol alloys. We first present a modeling approach in which systematic
density functional calculations and relationships between strains and total energies are employed to predict elastic
stiffness constants C11,C12 and C44, from which Poisson's ratio and Young's modulus are calculated. This modeling
approach is also used to simulate elastic constants for the iron-aluminum alloy known as Alfenol, which is shown to
exhibit similar behavior. We also use these models to simulate the relationship between strains along orthogonal
crystallographic directions as an alternate approach for predicting Poisson's ratio values. The second portion of this
paper addresses the experimental aspects of this study. Tensile tests of single-crystal Galfenol specimens with
compositions of 12 to 25 atomic percent gallium were conducted to determine the composition dependent values of
Young's modulus and Poisson's ratio. These experimental results are used to validate model predictions and to provide
experimental data to further aid in visualizing trends in elastic properties. This project will enable future researchers to
refer to the elastic properties of the alloy obtained using two different techniques, as well as enable them to select the
alloy with optimum elastic properties for their applications.
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