Abstract
Giant magnetostrictive materials (GMM) can be integrated in actuator or sensor applications. The design of these systems is optimized based on a good knowledge of the material properties and conditions of use. Terfenol-D exhibits the greatest room temperature strain among commercially available GMM, however, its magneto-elastic behavior is very sensitive to pre-stress level. In this work, the design of an experimental setup dedicated to the characterization of GMM magneto-mechanical behavior under constant stress is described. A major difficulty is to master the mechanical boundary conditions while the sample is subjected to dynamic magnetic loading. The dynamic stress experienced by the sample is connected to the magnitude of the magnetostriction strain, the stiffness of the sample and the stiffness of the characterization setup. Results show that an appropriate setup is able to reduce the dynamic stress variations induced by magnetic excitation variations below 0.1 MPa, while this dynamic stress can reach up to 20 times the magnitude of the applied stress when the control system is not used. With the boundary conditions being controlled, magnetic and magnetostrictive behavior of Terfenol-D are characterized under various uniaxial compressive stress levels, from the stress-free conditions to 90 MPa. By comparing the results obtained under controlled and non-controlled stress conditions, it is shown that uncontrolled boundary conditions can be responsible for errors of several percent on the magnetic induction measurement. The measurement of strain is even more sensitive to the boundary conditions, with errors up to 40% and 30% on the longitudinal and transverse strains, respectively. This work highlights the utmost importance to control the boundary conditions in order to characterize the magneto-mechanical behavior of GMM.
Highlights
Smart materials are widely used for sensor or actuator applications
This work emphasizes the great importance of accurately controlling the boundary conditions in order to characterize the magneto-mechanical behavior of giant magnetostrictive materials (GMM) such as Terfenol-D
The design of an experimental setup dedicated to the characterization of GMM magneto-mechanical behavior under uniaxial constant pre-stress has been described
Summary
Smart materials are widely used for sensor or actuator applications. In applications such as low voltage actuators, large force actuators, high power low frequency transducers or structural vibration control applications, giant magnetostrictive materials (GMM) can be interesting. Changes in magnetic and magnetomechanical properties of grain-oriented Terfenol-D samples have been studied, under pre-stress by Moffet et al using hydraulic pressurization [2], and after cycling by Prajapati et al using an electromechanically driven machine [19] In these works, control of loading boundary conditions or magnetic excitation was not discussed, but accurate measurement of pressure has been performed using a Bourdon tube and a pressure gauge, respectively. Pei et al [23, 24] studied the magneto-elastic behavior of Terfenol-D alloys and oriented materials In this setup, the mechanical force can be applied at any fixed angle with the magnetic field. All these works result in significant differences in the measurement of the magneto-mechanical behavior of Terfenol-D These differences are due to different compositions of the material tested [32], and to imperfect control of magnetic field and mechanical preload [9], especially for GMM. The influence of loading control conditions is studied and discussed
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