| Magnetorheological(MR)fluids are suspensions with micro particles or nanoparticles dispersed in carrier fluids,which are composed of iron particles,carrier fluids and various additives,which can transform from a liquid state to a semi-solid state in milliseconds in the presence of magnetic field,while regaining their original state once again when the magnetic field is removed,making them widely adopted in civil engineering,machinery,aviation,the automotive industry and the medical department etc.Various MR devices,such as MR dampers and MR brakes,are becoming indispensable mitigation devices in their related fields because of their excellent characteristics including adjustable damping force,low energy consumption as well as high precision.In order to achieve the effective mitigation effect of MR devices,MR fluids should have the characteristics of good stability and fluidity as well as high shear yield stress.At present,domestic and foreign scholars have done plenty of research on MR fluids and achieved some results,but there are still some problems remained to be solved,such as the coordination between stability and adjustability of MR fluids,the establishment of evaluation system of the comprehensive performance of MR fluids,the design of the shear yield stress test device as well as the bulid-up of the mechanical models that can accurately describe the interaction and transformation of the magnetic particles in MR fluids.Therefore,further development and study should be carried out on the restricted field of MR fluids.In this paper,a research method combined with performance tests and theoretical analysis at both macroscopic and microscopic level has been adopted from the optimization of material preparation to the improvement of both stability and adjustability based on the experience of advanced products of MR fluids at home and abroad.The preparation process and material ratio were comprehensively optimized contributing to the preparation of MR fluids with excellent comprehensive performance,and the evaluation method was proposed accompanied by the implementation of stability and adjustability tests to obtain the MR fluids sample with optimal comprehensive performance.In addition,the novel plate type shear yield stress testing device has been designed to carry out the shear yield stress test of MR fluids.Furthermore,the single-double chains micromechanical model of MR fluids was proposed,whose effectiveness has been validated through the comparison with the experimental results.Finally,the numerical simulation of the cable-magnetorheological damping system was carried out to verify the mitigation effect of the prepared MR fluids.The research work in this paper is elaborated in the following aspects:1)Ferromagnetic particles coated with multi-walled carbon nanotubes(MWCNTs)and graphene oxide(GO)composites were prepared,and the influence concerning ratio of MWCNTs,GO,grafting agent as well as carbonyl iron(CI)particles was studied to select the composite ferromagnetic particles which have the best effects of coating.And then,the selected MWCNTs/GO composites coated ferromagnetic particles and the surfactant modified ferromagnetic particles which were prepared by research group earlier were combined based on the complementary theory to prepare a series of MR fluids with different amount of the two composite ferromagnetic particles?volume fraction of total ferromagnetic particles and additives by the control variable method.2)Through the tests of stability,zero field viscosity and shear yield stress of the prepared MR fluids,the influence of different factors on the properties of MR fluids was studied.Furthermore,the evaluation method for the comprehensive performance of MR fluids was proposed contributing to the selection of MR fluids sample with the optimal performance.3)A novel plate type shear yield stress testing device has been developed according to the principle of the shear flow of MR fluids,which effectively combines the control of magnetic field,the measurement of shear stress and shearing mechanism together to generate a uniform and adjustable magnetic field up to 0.5T in the region of the MR fluids measured by the Hall sensor.4)The single-double chains micromechanical model of MR fluids was deduced considering the law and distribution as well as the transformation and transformation of microscopic morphology of MR fluids based on the theory of coupled field,and the accuracy of the model was verified by comparing the theoretical values with the experimental results.5)The mechanical model of MR damper is proposed based on the single-double chains micromechanical model,whose effectiveness was verified by the performance test of the MR damper.Simultaneously,the numerical simulations of the systems with and without the MR damper were carried out based on the LQR control algorithm and the semi-active control strategy to verify the mitigation effect of the MR fluids with comparison of the vibration response output by the two systems.The innovations of this paper lay in:1)The MWCNTs/GO composites coated ferromagnetic particles were obtained,and MR fluids with both MWCNTs/GO composites coated ferromagnetic particles and the surfactant modified ones were prepared.The results of the performance tests presented that the addition of the MWCNTs/GO composites coated ferromagnetic particles could significantly improve the stability of MR fluids while balance their adjustability.Simultaneously,the evaluation method for comprehensive performance of MR fluids was proposed.2)A novel plate type shear yield stress testing device has been developed,which could effectively combine the control of magnetic field,the measurement of shear stress and shearing mechanism together.3)The single-double chains micromechanical model of MR fluids was deduced considering the transition and transformation of the micro-chain structure of MR fluid under different conditions,and the values were compared with the experimental results to verify the effectiveness of the model. |
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