Magneto-Mechanical Characterization of Magnetostrictive Composites

Abstract This paper describes magneto-mechanical test results for magnetostrictive composites. The purpose of the study is to evaluate the behavior of magnetosrictive materials under combined magnetic and mechanical loading, and to determine fundamental properties used for design of actuator and sensor systems that incorporate these materials. Currently the composites are being used in sonar transducers. The magnetosrictive composite contains Terfenol-D (Tb0.3Dy0.7Fe2) particulate embedded into an epoxy binder. Composite form is used due to the relative brittleness and limited operational frequencies of monolithic Terfenol-D. Three different tests were performed: 1) constant magnetic field with linearly varying load, 2) constant magnetic field with cyclically varying load around a bias load and 3) constant pre-load with varying magnetic field. Testing was performed on five different volume fraction composites, namely, 10%, 20%, 30%, 40% and 50%. Parameters that were evaluated include strain output, magnetic field and elastic modulus. Results for the constant magnetic field tests indicate that modulus generally increases with increasing volume fraction and increasing H/Hmax. However, for low fields, an initial dip is noticed in modulus (i.e. ΔE effect) attributed to domains becoming more mobile at lower magnetic field levels. Results for the constant load test indicate a strong dependence of strain output on applied pre-stress. Results indicate that max strain peaks at a certain value of the pre-stress and then decreases for increasing pre-stress.