Development of highly magnetostrictive composites for applications in magnetomechanical torque sensors
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The objective of this work was to investigate and develop a new type of magnetomechanical material with high magnetomechanical response and low hysteresis. This material will be used in electronic torque sensors. A major appreciation could be for advanced steering systems in automobiles which will replace the fuel inefficient hydraulic steering systems currently in use;The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles was studied. Both experimental and modeled results showed that the elastic modulus of the matrix is an important factor determining the magnetostriction of the composite. For a series of composites with the same volume fraction of Terfenol-D particles but different matrix materials, the saturation magnetostriction was found to increase systematically with decreasing modulus of the matrix;A magnetic torque sensor test bed was developed as part of the present investigation. This instrumentation was used to make the magnetomechanical measurements under torsional stress. After investigating both of the H-sigma processes and sigma-H processes of metal rods (Fe, Co, Ni), it was shown that a high piezomagnetic coefficient, together with a high saturation magnetostriction are two "figures of merit" for choosing materials for magnetomechanical sensors;A new class of materials, metal-bonded (Ag/Ni/Co) Co-ferrite composites, has been found to be better than the traditional magnetostrictive materials for this application. These materials exhibited magnetostriction in excess of 200 ppm and a d33 Coefficient, 1.3 x 10--9 A--1m. A prototype of torque sensor was constructed from this material. The sensitivity of surface magnetic field to applied torque as high as 65 AN--1m--2 in the torque range of +/-10N·m was observed. The temperature dependence of the magnetomechanical sensitivity and hysteresis were measured over the range --37 to 90°C. Both decreased as the temperature increased throughout the entire range. The magnetomechanical hysteresis became negligible at temperatures higher than 60°C, above which it gave a linear magnetic field change in response to torque;The magnetomechanical effect under torque was modeled with an extension of the existing uniaxial model of the magnetomechanical effect. The modeled results show similar behavior to the experimental results and give quantitatively realistic values of sensitivity and hysteresis.