Mechanical behavior and auxetic properties of galfenol

Abstract

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 C 11 ,C 12 and C 44 , 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.