Stability Control Of Magnetorheological Fluid And Its Application In Key Engineering

Magnetorheological (MR) fluids are one kind of new intelligent materials with great application prospects. MR intelligent devices can realize the initiative or semi-active intelligent damper, and solve some hard tasks, such as damping the dynamic responses of key engineering. However, there is still no significant practical breakthrough in key engineering application. One of the most critical bottlenecks is that sedimentation and settlement status evaluation of MR fluids, and the conflict between the stability and rheological property of MR fluids, still are challenging problems not yet solved very well.Aiming at the intelligent control of the longitudinal vibration response induced by train-braking on Wuhan Tianxingzhou Cable-stayed Bridge, and severing it as a breach, opening the range of application of MR fluids in key engineering. Researched and developed the methods of grafting surface modifier on the surface of magnetic particle, tuning the interface characteristics of magnetic particles, and collaboratively controlling the stability and rheology of MR fluids by surface modification of magnetic particles and nanoparticles; Analyzed the mechanism and principle of controlling the stability of MR fluids by surface modification of magnetic particles: solubilizing and viscosifying to reduce the settling velocity, and compatibilizing to reduce the sedimentation ratio, increasing Zeta potential to improve the dispersion stability, shielding effect to enhance the oxidation resistance, improving wettability to enhance redispersibility of MR fluids. Studied the relationship between the yield stress of MR fluids and their volume fraction of magnetic particles and the applied magnetic field intensity, and got two linear analysis models.The prepared MR fluid sample is proved to be high stability and high yield stress by passing through the long-term stability and rheological properties test, and the mechanics performance test of the MR damper prototype made with the home-made MR fluid sample; Then mass produced500L MR fluids with high stability, high yield stress and lower off-state viscosity, and produced12×500kN MR dampers with the home-made MR fluid, and installed them between the deck and lower cross beam at each tower of Tianxingzhou Yangtze river bridge for intelligent controlling the longitudinal vibration response induced by train-braking on Wuhan Tianxingzhou Yangtze river cable-stayed bridge. The simulation results show that the maximum of longitudinal displacement of deck will be sure smaller than30mm in all cases through semi-active control strategy by these12400kN MR dampers, even if in the most serious case, the maximum of longitudinal displacement of deck would fall from149.2mm down to19.4mm, reduced by87.0%. Finally, the world’s first breakthrough of intelligent control of vibration response of large bridge by MR dampers has become truth.