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Nowadays, many scholars have been studied the normal force of MRF in the uniform magnetic field. However, the research on the normal force of MRF in the non-uniform magnetic field is relatively limited. The non-uniform magnetic field can cause the MRF to generate normal force of different sizes and directions to cope with different working conditions, thus the normal force generated in the non-uniform magnetic field require more attention. In this paper, a theoretical model of the normal force of MRF in the non-uniform magnetic field was developed based on the enhanced magnetic dipole model. The normal force of MRF within a unit area can be calculated based on this theoretical model. However, the magnetic induction intensity is different at different locations of the non-uniform magnetic field, which leads to the normal force generated by the MRF are not accurately calculated. Therefore, it is necessary to use COMSOL to establish the material model of the MCR-302 plate rheometer and MRF to verify the accuracy of the proposed model. Then a flat-plate rheometer was used to test the static normal force of the MRF in the non-uniform magnetic field. Finally, the simulation and experimental data were compared. The results show that the simulation result with the experimental data is a good agreement, which verifies the reliability of the theoretical model. The static normal force of the MRF increases with the increase of volume fraction and magnetic field intensity. [ABSTRACT FROM AUTHOR]

The normal force of magnetorheological (MR) fluids in porous foam metal was investigated in this paper. The dynamic repulsive normal force was studied using an advanced commercial rheometer under oscillatory shear modes. In the presence of magnetic fields, the influences of time, strain amplitude, frequency and shear rate on the normal force of MR fluids drawn from the porous foam metal were systematically analysed. The experimental results indicated that the magnetic field had the greatest effect on the normal force, and the effect increased incrementally with the magnetic field. Increasing the magnetic field produced a step-wise increase in the shear gap. However, other factors in the presence of a constant magnetic field only had weak effects on the normal force. This behaviour can be regarded as a magnetic field-enhanced normal force, as increases in the magnetic field resulted in more MR fluids being released from the porous foam metal, and the chain-like magnetic particles in the MR fluids becoming more elongated with aggregates spanning the gap between the shear plates. [ABSTRACT FROM AUTHOR]

This paper presents the normal force phenomena for static and steady shear mode in magnetorheological (MR) fluid. The results of the study show that, in the static mode, with the magnetic flux density increasing, the normal force will increase until the maximum, and then reduce to a steady value, and during the increasing stage, it can be expressed as F N =4667* B 2.48 approximately; however, in the steady shear mode, only when the magnetic flux density achieves a certain value, the normal force phenomena will be observed clearly, and with the increasing of magnetic field, the normal force reaches the maximum, and then also decreases to a steady value. Besides, by defining the time parameters of dynamic response, the dynamic response of normal force is studied. If the shear plate is stationary, from the magnetic field on to a stable normal force produced, the response time is about 25.11 ms. [ABSTRACT FROM AUTHOR]

Abstract: The normal forces of magnetorheological fluids under oscillatory shear are investigated by a commercial magneto-rheometer with plate–plate geometry. At the constant strain amplitude and frequency, the normal forces almost keep a steady value with the testing time if the strain amplitude is smaller than the critical value. When a larger strain is applied, they will fluctuate periodically. Under the strain sweep mode, the relationships between normal forces and strain amplitude can be divided into three regions: linear viscoelastic region, nonlinear viscoelastic region and the viscoplastic region. Under the frequency sweep method, it is found that the angular frequency show little influence on the normal forces. At last, the normal forces increase with increasing of the temperature under a low magnetic field, while they decrease under a high magnetic field. [Copyright &y& Elsevier]