The torque characteristics of magnetorheological brakes, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnetic casing, are controlled by regulating the yield stress of the MR fluid. An increase in yield stress increases the braking torque, which means that the higher the yield strength of the MR fluid, the better the performance of the MR brake will be. In the present research an application of compressive force on MR fluid has been proposed to increase the torque capacity of MR brakes. The mathematical expressions to estimate the torque values for MR brake, operating under compression plus shear mode accounting Herschel–Bulkley shear thinning model, have been detailed. The required compressive force on MR fluid of the proposed brake has been applied using an electromagnetic actuator. The development of a single-plate MR disk brake and an experimental test rig are described. Experiments have been performed to illustrate braking torque under different control currents (0.0–2.0 A). The torque results have been plotted and compared with theoretical study. Experimental results as well as theoretical calculations indicate that the braking torque of the proposed MR brake is higher than that of the MR brake operating only under shear.

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Smart Science 65 Particle size distributionAs per Lemaire et al.[4] small sized particle means diameter = 0.5 µm and large sized particle means diameter = 1.0 µm. As per Kittipoomwong and Klingenberg [5], the larger size means two times the size of smaller size particle. Chiriac and Stoian [6] termed particle lesser than 20µm as smaller sized particle, while particles in the range of 50 to 63 µm were named as larger sized particles. This review of literature intimates the subjective nature of term "larger sized" and "smaller sized" particles. In the present case, two commercial carbonyl iron powders; and product no. 12310 and 44890 from Sigma Aldrich, were purchased. The product no. 12310 contains approximately 10% in the range 150µm -212µm, 65 -85% in the range of 45µm -150µm. Therefore the Product No. 12310 is named as "large sized particles". The particle size distribution in product No.

A magnetorheological brake, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnet, is proposed to replace the conventional heavy weight low response hydraulic disk brake. The frictional characteristics of the proposed brake can be controlled by regulating the yield stress of the MR fluid as function of magnetic field and normal compressive force. The controllable yield stress retards the surfaces of rotating disks, thus MR fluid can be used as a brake lining material. The present research work attempts designing a squeeze film MR brake by accounting compression enhanced shear yield stress of magnetorheological fluid. Theoretical calculations indicate that the estimated braking torque of the six plate squeeze film MR brake, under compression, is in the order of 600Nm. To validate the theoretical design and its findings, a prototype of single-plate squeeze film MR disk brake has been developed. Experimental test setup helps to illustrate braking torque under different control currents (0.0 to 1.25 A).

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A conventional disc wears out and the brake pollutes the environment. Brake pad dust is reported to be the largest source of environment pollution 1 . The particles emanating because of wear of the brake pad pollute the environment 2,3,4 . In addition to pollution caused by wear particles, the friction-induced noise between the brake pad and the disc is also a major concern 5 . Also, localized heating occurs in a conventional disc brake. To tackle both of these problems, conventional disc brakes can be replaced with manetorheological fluid brakes. Magnetorheological fluids are materials having a shear yield stress which is a function of the magnetic field. On the application of a magnetic field, magnetorheological particles become aligned and increase the shear resistance between relatively moving surfaces. The friction between the stator and the rotor increases and fulfils the braking function, which means that magnetorheological fluids can be used as brake friction materials. A magnetorheological brake consists of a rotating disc or discs immersed in a magnetorheological fluid and enclosed in an electromagnetic casing. The torque characteristics of the magnetorheological brake in the shear mode are controlled by regulating the yield stress of the magnetorheological fluid. An increase in the yield stress increases the braking torque, which means that, the higher the yield strength of the magnetorheological fluid, the better is the performance of the magnetorheological brake. However, the major disadvantage of the shearmode-based magnetorheological brake is its high resisting torque even in the off-state viscosity, and such magnetorheological brakes cannot be recommended for automotive applications. To obtain the performance of a conventional disc brake, experimental studies on a conventional disc brake were performed using a full-scale dynamometer. In addition to wear particles, localized heating of the disc was observed. The disc-pad interfaces were modelled to simulate the disc temperature. The values of the maximum temperature, which were obtained from simulations as well as experiments, were compared. The simulations were extended to hypothetical 360°pads, and a significant reduction in the maximum temperature was noted. Based on the idea of 360°pads, a magnetorheological brake subjected to shearing was analysed.To perform experiments on a small-scale magnetorheological brake, a test set-up was designed and developed, and it was confirmed that a magnetorheological brake subjected to shearing provides a better torque than does a conventional disc brake of the same size. An ideal magnetorheological brake should exert a zero frictional torque in the off-state condition and a controllable frictional torque in the on-state condition. An attempt was made to design such a magnetorheological brake. To overcome the disadvantage of the shear-mode-based magnetorheological brake, a new design of magnetorheological brake with a slotted disc was proposed. The design and development of the proposed magnetorheological brake...

In this paper, numerical simulations of lubricating grease flow in the grease pocket of a double restriction seal geometry using computational fluid dynamics are presented. The grease is treated as a singlephase Herschel-Bulkley fluid with different rheological properties corresponding to NLGI grade 00, 1 and 2. The numerical code and rheology model have been validated with a semi-analytical solution based on flow measurements using microparticle image velocimetry. The flow has been modelled for low and high rotational speeds driving the flow, and elevated temperatures. Also, the evolution of contaminant particles in the grease pocket is investigated. It was found that the flow and velocity distribution in the pocket-and consequently the contaminant particle concentration evolution, is characterized by the shear thinning rheology of the grease. With higher shear rates in the grease and higher temperatures, the grease approaches a more Newtonian type of behaviour leading to a reduced yield and shear thinning characteristics directly affecting the grease ability to transport contaminant particles.

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