Papers by Author: Guo Jun Yu

Abstract: A type of Magneto-Rheological Materials (MRMs) was prepared. The off-state viscosity and the shear stress of the MRMs were characterized and studied by an advanced rotational rheometer system. A kind of Self-Decoupling Magneto-rheological (SDMR) damper was established based on these MRMs. An intellectual isolation system for grid structures was obtained by integrating SDMR damper and isolation device. The seismic whiplash effect of the top bent frame column and space grid roof of the hydropower plant could be reduced. Furthermore, the half stable increment method was proposed as the semi-active strategy. The results indicated that the SDMR dampers used at the grid roof supports setting plate rubber bearings can significantly improve the vibration performance and energy dissipation structure roof isolation system in different seismic intensity. In addition, these SDMR dampers can effectively reduce the lateral slippage of the plate rubber, so as to avoid failure or damage of the isolation system because of the transfinite horizontal displacements. Compared with the conventional damper only in case of multiple earthquakes, the damping force and adjustable multiple of this SDMR damper have better adaptability, and this SDMR damper provides a higher safety factor.

Abstract: In this paper, we establish the mechanical property analysis of Single-walled Carbon Nanotubes (SWCNTs) modified beam element model based on the molecular structural mechanics method. Then we study the mechanical properties of their radial direction characteristics using the finite element software Abaqus. The model simulated the different bending stiffness with rectangular section beam elements C-C chemical force field. When the graphene curled into arbitrary chirality of SWCNTs spatial structure, the adjacent beam position will change the moment of inertia of the section of the beam. Compared with the original beam element model and the calculation results, we found that the established model largely reduced the overestimate of the original model of mechanical properties on the radial direction of the SWCNTs. At the same time, compared with other methods available in the literature results and the experimental data, the results can be in good agreement.

Abstract: The modified carbonyl iron powders with single particle size (single-grading) and binary particle sizes (double-grading) were added in the composite gel, which was prepared by using methyl silicone oil, gelatin and agaropectin colloids as raw materials, and then the single-and double-grading magnetorheological composite gels (MRCGs) were prepared by vacuum decompression. The effects of particle size and gradation of carbonyl iron power on the rheological behavior of the MRCGs were studied. The results show that the shear strength of single-grading MRCGs decreased gradually with the decrease of the carbonyl iron particle size. However that the shear strength of the double-grading MRCGs with the gradation of 90 wt% un-ball-milled and 10 wt% ball-milled carbonyl iron powders first increased then decreased with the elongation of milling time (the decrease of carbonyl iron paticle size) and reached 99.6kPa when ball milling time for 24h, which was 17.8kPa larger than that of un-ball-milled single-grading MRCGs.

Abstract: In this paper, on the basis of the viscoelastic fractional derivative model, Mittag-Leffler function is applied to deduce the expression of stress relaxation modulus for magnetorheological elastomers according to its form and main properties. Furthermore, the relaxation modulus for polyurethane rubber matrix cured magnetorheological elastomers at different applied magnetic fields and shear strains is tested by rheometer. The results indicate that magnetorheological elastomers exhibit obvious relaxation behavior and the magnetic field strength and shear strain exert significant influence on the relaxation behavior: the relaxation modulus of magnetorheological elastomers increases with the magnetic field strength but decreases with the shear strain. Besides, the model agrees well with the experimental data which indicates that the model is suitable for characterization of relaxation behavior for magnetorheological elastomers.

Abstract: In this paper, the influence of the soft magnetic particle content on the properties of MRFs is studied. Besides, the relationships between the shear stress of MRFs and the magnetic induction intensity, the soft magnetic particle content, and the shear rate are discussed. The curve equation that expresses the relationship between the shear stress, the magnetic induction intensity, and the soft magnetic particle content is established through the fitting of experimental data. The results show that the shear stress of MRFs increases with increasing magnetic induction intensity and that the shear stress will tend to stabilise when the magnetic induction intensity reaches a sufficient value. The validity of the Bingham model and the H-B model for describing the relationship between the shear stress and shear rate is established, and the phenomenon of shear thinning of MRFs can be better represented by the H-B model than by the Bingham model.

Abstract: The influence of carbonyl iron particles sizes on the properties of magneto-rheological fluids (MRFs) were studied. Different-sized carbonyl iron magnetic particles were prepared by ball milling with different milling times. On this basis, different particle MRF were prepared The off-state viscosity and the shear stress of the above MRFs were characterised and studied by an advanced rotational rheometer system. The test results show that the off-state viscosity and the shear stress of single-particle MRFs were enhanced with increasing average carbonyl iron particle size at a constant magnetic field. The shear stresses of MRFs containing two or three different particle sizes were significantly improved compared with the MRFs containing only a single particle size. At a reasonable level of medium and small size carbonyl iron particle spread throughout the structure of the multiple-particle MRFs, the defects in the chain structure were remedied when a chain reaction occurred, and the mechanical properties of MRFs were enhanced. Meanwhile, increased mass fractions of the small size carbonyl iron particle resulted in a reduction in overall average particle size of MRFs, and the mechanical properties of MRFs were also reduced. The mechanical properties of multiple-particle MRFs were observed to be strongly dependent on the size and mass fraction of the medium and small carbonyl iron particles.

Abstract: Numerical simulation and experimental analysis for a magnetic circuit model of a damper were carried out by adjusting the size of the auxiliary gap to obtain greater magnetic field strength and wider adjustable multiples of the damping force. Results of experiment indicate that there is a specific ratio of sizes between the auxiliary gap and the working gap; this gap ratio is 3:1. The adjustable multiple and gap ratio is validated by the results of the experiment. The largest value for the magnetic induction in the working gap can reach 80–90% of the maximum; the least value is close to zero, and the adjustable multiple of the magnetic induction is near about a factor of 7. Experimental data also indicate that the law of the magnetic flux leakage is affected by the size of auxiliary gap as well as the intensity and direction of the current. Performance testing of the real optimal damper reveals that the maximum damping force of the damper is 195.7 kN, which is ~92.7 percent of the theoretical maximum value, at a gap ratio of 1:2.5.

Abstract: Based on electromagnetic-thermal coupling field mechanism, a large-scale finite element analysis model for electromagnetic-thermal coupling global damper is established by ANSYS software. Electromagnetic field and temperature field sequential coupling analysis method is used in this study. Relative permeability and resistivity of magnetic material with temperature is also considered in the FE model. The simulation results show that the temperature of self- decoupling magnetic damper rises rapidly under external excitation, the temperature changes the magnetic fluid yoke and the materials’ core parameters, magnetic flux density in damper channel gradually decreases with the time, and the damping force decreases, finally the high temperature decline phenomenon is revealed.

Abstract: Nanometer calcium carbonate (nano-CaCO3) is an inorganic material that does not have the rheological properties of a magneto-rheological fluid (MRF) but has some effects on the sedimentary stability and rheological properties of MRF. The MRF was prepared by adding nano-CaCO3 to improve its comprehensive and practical properties. The results showed that, with an increase in the amount of nano-CaCO3, the sedimentary stability of MRF would be improved. The off-state viscosity of MRFs increased with an increasing amount of nano-CaCO3. The shear stress of MRF was decreased slightly by adding nano-CaCO3. To some extent, the comprehensive and practical properties can be improved by adding a certain amount of nano-CaCO3. However, there is also certain localization that properties of MRF are improved by adding Nano-Inorganic Materials in the high temperature environment.