Papers by Author: Cheng Bin Du

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: The stability of a cantilever column subjected to a subtangential follower force and a vertical force is discussed for investigating the effects of these factors on the critical force. The governing differential equation of the system and the corresponding boundary conditions are established, and the exact solution is found out by integrating the differential equation. Based on the exact solution, the effects of the parameters relating to the subtangential follower force and the vertical force on the critical force are analyzed, and discussions for these results are performed， the influence curves of the subtangential follower force parameter and the vertical force parameter to the critical force are plotted. The results show that the parameter of a subtangential follower force can be bigger than 1/2, even equal to 1.0, with taking into account of the effect of the vertical force.

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.

Abstract: The hydrophilic-lipophilic balance (HLB) parameters of surfactants have a significant effect on properties of surfactants and determine the effects of surfactants. The magneto-rheological fluid (MRF) is prepared by using the two typical HLB parameters of surfactants including Polyethylene Glycol and oleic acid in order to improve the property of MRF. Polyethylene Glycol (PEG) whose HLB parameter is 20 has strong hydrophilic. Oleic acid whose HLB parameter is 1 has strong lipophilic. The results indicate that magnetic properties of magnetic particles and rheological properties of MRF can hardly be changed by adding surfactants. The sedimentary stability of MRF adding lipophilic surfactants is superior to that of MRF adding hydrophilic surfactants, and the stability of MRF adding two surfactants increases significantly.

Abstract: Based on the characteristics of magneto-rheological fluid, a new type of transmission device has been developed in this paper, in which output torque can be controlled accurately by adjusting electric current. It can be applied to replace magnetic particle clutch widely used at present to achieve tension control in some small-sized winders. A structure design of prototype has been proposed. By using the Bingham plastic constitutive model, the output torque of the device has been derived. Electromagnetic finite element analysis has been employed to simulate the magnetic circuit of this magneto-rheological fluid tension control device. It is shown that this magneto-rheological fluid tension control transmission has its significant advantages comparing with traditional magnetic particle clutch. The new one can produce higher controllable torques, and may be applied widely in the future.

Abstract: A numerical method from the mesoscopic point of view is proposed to describe the fracture process of concrete. At mesoscopic level, concrete is considered as a three-phase composite consisting of mortar matrix, coarse aggregate and interfacial transition zone (ITZ) between them. According to the grading of coarse aggregate obtained from sieve analysis, the random aggregate models with polygonal aggregates were generated by Monte Carlo random sampling principle. In this work, the tensile cracking is assumed to the only failure criterion at the mesoscopic scale; and the stress-separation law based on the fictitious crack model is adopted to allay the sensitivity on mesh size in the softening regime. The nonlinear finite element method is used in the simulation of concrete under bend loading. The influence of the shape of aggregate on the macroscopic response of concrete is also investigated. Numerical results show that the strength of the specimen with circular aggregate is higher than the specimen with arbitrary polygonal aggregate. The predicted bending strength agrees well with experimental data.

Abstract: Concrete is taken as three-phase composites consisting of aggregate, interface and mortar matrix in the paper. The tensile strength and elastic modulus of each phase material are assumed to obey Weibull distribution. A few random aggregate and random parameter models are generated by Monte-Carlo method. Tensile failure of micro element is described by tension damage model, in which the stress will be reduced linearly after the stress reaches the maximum tensile strength. The results show that more cracks of lower homogenous specimens are observed than those of higher homogenous specimens. The phenomenon of discontinuous cracking is observed in the former, while strain localization and brittle behavior is observed in the latter. The ultimate load obtained in the numerical simulation agrees well with that of the test.