Magneto-elastic characterization and thermal stability of the composite materials made of magnetic and non-magnetic constituents
Hison, Cornelia Lorelai (2006) Magneto-elastic characterization and thermal stability of the composite materials made of magnetic and non-magnetic constituents. [Tesi di dottorato] (Inedito)
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The research activity developed in the frame of the doctoral thesis is basically focused on the development, elastomagnetic behavior characterization and performance investigation (in view of application as core material for sensors and actuators) of the elastomagnetic composites made of magnetic micro-particles uniformly dispersed inside a non-magnetic, elastomeric matrix. These composites, exhibiting elastomagnetic effects different from the classical magnetoelastic ones (i.e. Joule and magnetomechanical effects), are expected to be the precursors of an important class of multifunctional materials due to their peculiar, specific elastomagnetic performances and unique ability to detect and actuate deformations at the same time. The thesis is structured in eight chapters and general conclusions. At the beginning (Chapter I) of the thesis, the most recent and relevant state of the art in composite materials consisting of magnetic particles dispersed in a non-magnetic, elastic matrix are reviewed. There are pointed out their strengths, as well as their weaknesses which give the premises for the development of the elastomagnetic composites. In Chapter II are presented the developed elastomagnetic composites, describing thoroughly their preparation process, and pointing out their key required characteristics: the magnetic mico-particles (soft ferromagnetic or small permanent magnets) must exhibit a strong coupling between the magnetic moment and their body; the composite matrix must have a good elastic behavior up to relative deformations of about 15%. The thesis is continuing with the introduction of the elastomagnetic effects (Chapter III), followed by the presentation of their theoretical model (Chapter IV). The experimental verification of the direct and inverse elastomagnetic effects is presented in Chapters V and VI, respectively. The obtained experimental results are consistent with the theoretical predictions, proving definitively the self-consistency of the developed elastomagnetic model. Based on the predictions of the experimentally validated theoretical model of the elastomagnetic effect, deformation and vibration detection sensor and actuator prototypes with elastomagnetic core materials were developed. In Chapters VII and VIII are presented in detail the sensing/actuating core material preparation, the developed sensor and actuator prototypes, the functioning models and their experimental verification and validity limits, the used experimental set-ups and investigation techniques of the core performances, concluding with the presentation of the optimum production parameters required to obtain the best sensing/actuating performances and their competitiveness with the standard materials actually used for similar target sensors and actuators. The last chapter is focused on the investigation of the developed elastomagnetic composites stability under dynamic mechanical solicitation and with the temperature, considering that the assessment of the thermal stability and mechanical ageing is a matter of strong interest for the engineering process of these composites as core material for sensors and actuators. In the Conclusion, a critical analysis of the obtained results is performed, emphasizing the original contribution brought by the researches developed in the frame of this thesis to the incremental improvement of the state of the art in the field of composite materials made of magnetic particles inside a non-magnetic, elastic matrix. Finally, there are also discussed the future trends, giving an insight into the future development of the elastomagnetic composites as core materials for intelligent devices.
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