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Development of Magnetorheological Elastomer System for Adaptive Vibration Isolation
Civil and Environmental Engineering
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ABSTRACTThis main objective of this study was focused on a proof-of-concept study of the performance of an adaptive bearing (AB) system under traffic and wind loadings, featuring magnetorheological elastomers (MREs). MREs were utilized to generate adaptability (variable stiffness) to the AB system. The investigations of this project were fundamental and developmental studies ranging from material synthesis, material characterization, theoretical studies, design and fabrication of the AB system, and large-scale component testing and evaluation. In addition, since no fabrication and testing systems were available in the market, testing and fabrication units were developed to facilitate the manufacturing of small and large-size MRE specimen, and a double-lap shear test unit to characterize MRE samples based on the ASTM standards. Project started with an extensive literature survey to identify feasible material compositions that were reported to have achieved high magnetorheological (MR) effect under different loading conditions. Carbonyl iron, medium (Tap silicone and Natural rubber), and additives (Carbon black and Carbon nanofibers) mixed MRE’s were fabricated under applied magnetic field of 1.2 Tesla. Scanning electron Microscope (SEM) pictures of the MREs showed the chain-like structure within MREs. A small-scale shear and compression test setup was manufactured for the characterization of MREs. Quasi-static and sinusoidal cyclic experiments were performed to investigate the magnetic field-dependent change on MREs properties under simultaneous shear and compression loads.In second phase of the project, bridge load requirements were established under traffic and wind loads. A large-scale shear and compression test setup was designed and manufactured to study the performance of the AB system under combined and compression loads. Component tests were successfully performed on two quarter-scale prototype bearings, measuring the changes in the stiffness of the adaptive bearing under the applied magnetic field, strain level, loading frequency, and compression load. Finally, a seven-parameter viscoelastic model was developed and adapted to simulate the response of natural rubber – based MREs and concluded it can capture the behavior sufficiently accurate. Results demonstrated that plastic silicone MREs show high MR effect at lower strains and MR effect diminishes for large strains whereas natural rubber based MREs show uniform MR effect for strains up to 150%. Also, carbon black improves the base passive stiffness and carbon nanofiber improves MR effect due to magnetically permeable characteristics. Storage modulus, loss modulus, effective stiffness, and effective damping showed increasing trend with increased applied magnetic field. However, MR effect was reduced with increased frequency. Experimental results demonstrated that the effective stiffness of adaptive bearing increases with increased applied magnetic field.