| Magnetostrictive composites containing Terfenol-D particles dispersed within a polymer matrix presents high advantages when compared to the monolithic Terfenol-D. The higher frequency response of magnetostrictive composites increases power density and widens the design space for employing magnetostrictive materials. This dissertation focuses on the performance prediction, improvement of manufacturing craft, influential factors on its performance and applications in civil engineering of magnetostrictive composites.Firstly, consider the shape of the magnetostrictive particles in magnetostrictive composites was ellipsoid, which can be described by aspect, the relationship between effective magnetic field and applied magnetic field was established based on demagnetization effect. Combined with the relationship between magnetostriction of magnetostrictive particulate and effective field, the relationship between the magnetostriction of single particle to the applied field was also built up. Then treating the magnetostriction of particulate as an eigenstrain, the average magnetostriction of the composites under any applied field as well as saturation magnetostriction was calculated based on Eshelby equivalent inclusion and Mori-Tanaka method. The calculation results indicated that the saturation magnetostriction of magnetostrictive composites increases with increasing particle aspect, particle volume fraction and decreasing Young'modulus of matrix, and the influence of applied field on magnetostriction of the composites becomes more significant with larger particle volume fraction or particle aspect.Secondly, an improved method was developed to overcome the shortcomings of traditional craft of preparing magnetostrictive composites. Magnetostrictive particulates was evenly mixed with liquid resin system by ultrasonic, then large orientation field was applied by an electrical magnetic field system until the resin become gel and the mixture system was supposed to be stable. Then, the mixture was placed in an oven and cured at high temperature for several hours. Test on magnetostriction of polyester resin-bonded Terfenol-D composites prepared by traditional method and improved method indicated the new craft could promote the magnetostrictive properties of magnetostrictive composites. Besides, the mechanism of the influence of dispersion method, orientation field and cure temperature on properties of magnetostrictive composites was discussed.Thirdly, the effects of orientation field, particle volume fraction, particle size distribution, cure temperature, polymer matrix and blending with other particles on properties of magnetostrictive composites were studied by experiment. The study on orientation field indicated that the saturation magnetostriction, the peak dynamic strain coefficient, the magnetomechanical coupling coefficient and the Young's modulus increase with an increasing orientation field. An optimal orientation field exists, the value of which depends on particle volume fraction, and no obvious improvement of the properties could be expected for an orientation field larger than the optimal value. The study on particle volume fraction indicated the magnetostriction increase dramatically with particle fraction at low particle volume fraction, but slightly at large levels. Both permeability and Young's modulus increase with increasing particle fraction. The composite with 30% particle volume fraction presents the largest compression strength. The study on particle size distribution indicated that the magnetostrictive properties increase with increasing particle size at small particle size level, but decrease at large size level. Magnetostrictive composite fabricated with polydispersed distribution particles presents the largest magnetostrictive properties. The study on cure temperature indicated that when the operating temperature was a constant, at the same magnetic field level, the magnetostrictive properties, such as magnetostriction, piezo-magnetic coefficient and relative permeability, increase with increasing cure temperature. The study on polymer matrix indicated that magnetostrictive composites fabricated with epoxy resin shows better performance than those fabricated with unsaturated polyester resin. The study on blending with carbonyl iron particles indicated that with the increase of the percentage of soft magnetic powder is the increase of magnetic permeability and decline of magnetostrictive properties. The study on blending with nano-SiO2 indicated the mechanical properties and magnetostrictive properties of magnetostrictive composites at low field can be promoted by blended with nano-particles.Additionally, this dissertation studied the magnetostrictive properties of magnetorheological elastomer (MRE), another kind of magnetostrictive composites which have not been sufficiently studied. Due to the interaction between silicon rubber matrix and carbonyl iron particulates, MRE exhibits large magnetostriction effect. The particles volume fraction is one of the important factors, which have great influence on the performance of MRE. At low-volume fraction levels, magnetostriction effect of MRE increases with increasing particle volume fraction. The increase of percentage of particles, which are aligned in the transverse direction during cure time, is beneficial to the improvement of saturation magnetostriction. The largest magnetostriction observed in tests was 184ppm, which was as large as piezoelectric ceramic, but was an order less than Terfenol-D. The performance of composites lacked repeatability resulted from the hysteresis effect and remnant strain after switching off the applied field; therefore, the magnetostriction of MRE was unstable.Finally, a semi-active friction damper was designed based on the properties of epoxy-bonded Terfenol-D composites with 53% particle volume fraction. Energy dissipation capacity under different magnetic field was tested and compared with the dampers actuated by Terfenol-D and PZT, which indicated the smart friction damper actuated by magnetostrictive composites presented both large tunable damping force and less cost. Then vibration control experimental was done on a model of stay cable by smart friction damper actuated by magnetostrictive composites. The results indicated that this kind of smart friction damper can decrease the vibration of stay cable effectively, especially by semi-active control method.
|
PDF Full Text Request