Statistical Analysis of Terfenol-D Material Properties

Abstract

This article focuses on the characterization of Terfenol-D material properties under magnetic bias, mechanical preloads, AC drive fields, frequencies of operation, and mechanical loads typical of many dynamic transducer applications. These are test conditions unlike those in most Terfenol-D characterization studies. The article also provides an explanation for prior experimental studies which suggest that significant variation in material properties are expected in Terfenol-D elements subjected to repeated tests under fixed operating conditions. Through a statistical framework for the design of experiments and data analysis, we conducted repeatability tests which demonstrate that such variations are likely to be due to imperfect control of the magnetic bias and mechanical preload from test to test, and not to intrinsic material behavior. Frequency response measurements from near DC to past the test transducer's fundamental frequency were combined with classical electroacoustics theory to determine the functional dependence of magnetoelastic properties with respect to varying operating regimes. These properties include two elastic moduli, piezomagnetic coefficient, magnetomechanical coupling coefficient, and two magnetic permeabilities. Analysis of variance (ANOVA) calculations were employed to determine 95% prediction and confidence intervals for the overall material property trends and coefficients of variation associated with the repeatability tests.