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A magnetorheological fluid (MRF) is one of many smart materials that can be changed their rheological properties. The stiffness and damping characteristics of MRF can be changed when a magnetic field is applied. This technology has been successfully employed in various low and high volume applications, such as dampers, clutches, and active bearings, which are already in the market or are approaching production. As a result, the sealing performance of MRF has become increasingly important. In this study, the wear properties of seals with MRFs were evaluated by a rotary-type lip seal wear tester. The test was performed with and without a magnetic field. The leakage time was monitored during the tests in typical engine oil conditions. The results showed that the wear resistance of the seal with MRF was decreased under the magnetic field. [ABSTRACT FROM AUTHOR]

A magnetorheological fluid (MRF) is one of many smart materials that can be changed their rheological properties. The stiffness and damping characteristics of MRF can be changed when a magnetic field is applied. This technology has been successfully employed in various low and high volume applications, such as dampers, clutches, and active bearings, which are already in the market or are approaching production. As a result, the sealing performance of MRF has become increasingly important. In this study, the wear properties of seals with MRFs were evaluated by a rotary-type lip seal wear tester. The test was performed with and without a magnetic field. The leakage time was monitored during the tests in typical engine oil conditions. The results showed that the wear resistance of the seal with MRF was decreased under the magnetic field. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are smart materials that have been studied widely for their material properties. The elasticity modulus or hardness of an MRE can be changed when an external magnetic field is applied. In this study, a study of MREs applied to rolling friction control under various external magnetic strengths is conducted. To accomplish this, the rolling friction property of an elastomer on a rigid plate is analyzed. Then, MREs are prepared, and a rolling friction tester is designed to evaluate the changes in the rolling friction coefficient. The results show that the rolling friction coefficient can be changed with different magnetic field strengths. The rolling friction coefficient of the MRE can be controlled by the applied magnetic field, which can be applied to control the slip rate and be adapted to achieve the optimal friction effect in the future. [ABSTRACT FROM AUTHOR]

The dispenser ejects the ceramic filler and phosphor-containing liquid for making various products. When the particle-containing liquid is ejected under high-velocity conditions, however, the ejection reliability decreases because of the wear of the contact surface between the rod and nozzle even though these components are made of hard materials. It is therefore necessary to characterize the friction and wear properties of the hard materials, tungsten carbide (WC) and zirconium (Zr), with the high-viscosity liquid-containing nitride or yttrium aluminum garnet (YAG) particles under reciprocating conditions. Particle contents of 15 wt.% and 30 wt.% are added to the liquid. A reciprocating test was implemented to this end, and WC and Zr specimens were used. The liquid used in the experiment contains nitride and YAG. The experimental results show that the particles inside the liquid are worn out, leading to particle lubrication and the decrease in the coefficient of friction. Also, it is confirmed that the more the particles are, the less the coefficient of friction is due to particle lubrication. For each experimental condition, the coefficient of friction is measured and compared. Moreover, the contact surface of the specimen is analyzed using an electron microscope, and a profilometer is used to measure the surface roughness of the specimen before and after the test. The reciprocation friction and wear characteristics of WC and Zr with phosphor-containing liquid are evaluated by analyzing the experimental results. [ABSTRACT FROM AUTHOR]

The friction and wear properties of four different types of magneto-rheological (MR) elastomer were investigated. The MR elastomers have different matrix materials and structures. Most MR elastomers have a silicone matrix, since it has a more significant MR effect under a magnetic field compared to other materials. The mechanical properties of silicone, however, are poor compared to other materials, so it is difficult to use them in engineering applications. Therefore, a new polyurethane matrix material was used to enhance the friction and wear properties of MR elastomer. Additionally, two different matrix materials (silicone and polyurethane) were synthesized, and MR elastomers were structurally combined to improve the friction and wear peiformance. The friction characteristics of each MR elastomer were evaluated under reciprocating operating conditions. Wear depth was also measured to estimate the wear resistance. The test results show that the friction and wear peiformance of the modified MR elastomers are enhanced compared with the silicone-based MR elastomer. [ABSTRACT FROM AUTHOR]

In recent years, through the development of three-dimensional (3D) printing technology, 3D-printed parts have been used in various industries, such as medical equipment and robotics. Various 3D printing methods have been developed. Today, a 3D printer can be used even in precision parts, such as bolts and bearings. In this study, journal bearings are manufactured by a 3D printer to evaluate friction performance and self-lubricating performance. The journal bearings are fabricated using two types of 3D printing method: fused deposition modeling (FDM) and selective laser sintering (SLS). The specimens manufactured by FDM are produced by plastic materials with three-layer thicknesses. Nylon-based materials and aluminum-based materials are used to fabricate the SLS specimen. Micropores are created in the specimens during the printing process. Therefore, the self-lubricating performance can occur by micropores. The experimental setup is designed and constructed to evaluate the friction performance by varying rotational speed and the radial load. Through this study, the self-lubricating performance and friction performance of 3D-printed journal bearings are evaluated, and proper operating conditions for 3D-printed bearings are suggested. [ABSTRACT FROM AUTHOR]

In recent studies, many mathematical models have been introduced to describe the shear deformation characteristics of a magnetorheological elastomer (MRE). Owing to its beneficial elastomeric characteristics, an MRE can be adopted in novel controllable devices such as friction dampers and brakes. In this study, mathematical models are introduced to identify the frictional behavior of an MRE under different magnetic field conditions. Specifically, the improved LuGre (I-LuGre) model and the strain-stiffening model are compared using a system identification method. To identify the model that best describes the stick/slip behavior of an MRE, a harmonic frictional force was exerted on its surface with magnetic fields of varying strength. The I-LuGre model showed a precise correlation with the experimental results, and the strain-stiffening model was shown to have a simple structure for describing the frictional phenomenon. The system output error of the I-LuGre model remained within smaller errors than that of the strain-stiffening model. The parameter variations of each model that can be utilized to construct a control strategy are provided herein. [ABSTRACT FROM AUTHOR]