• Title, Summary, Keyword: Sliding wear

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Stick-slip Characteristics of Magnetorheological Elastomer under Magnetic Fields (자기장에 따른 자기유변탄성체의 스틱 슬립 현상 연구)

  • Lian, Chenglong;Lee, Kwang-Hee;Kim, Cheol-Hyun;Lee, Chul-Hee;Choi, Jong Myoung
    • Tribology and Lubricants
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    • v.31 no.1
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    • pp.6-12
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    • 2015
  • This paper investigates the stick-slip characteristic of magnetorheological elastomer (MRE) between an aluminum plate and the surface of the MRE. MRE is a smart material and it can change its mechanical behavior with the interior iron particles under the influence of an applied magnetic field. Stick-slip is a movement of two surfaces relative to each other that proceeds as a series of jerks caused by alternate sticking from friction and sliding when the friction is overcome by an applied force. This special tribology phenomenon can lead to unnecessary wear, vibration, noise, and reduced service life of work piece. The stick-slip phenomenon is avoided as far as possible in the field of mechanical engineering. As this phenomenon is a function of material property, applied load, and velocity, it can be controlled using the characteristics of MRE. MRE as a soft smart material, whose mechanical properties such as modulus and stiffness can be changed via the strength of an external magnetic field, has been widely studied as a prospective replacement for general rubber in the mechanical domain. In this study, friction force is measured under different loads, speed, and magnetic field strength. From the test results, it is confirmed that the stick-slip phenomenon can be minimized under optimum conditions and can be applied in various mechanical components.

Tribology Characteristics in 200 μm of Hexagonal Array Dimple Pattern

  • Choi, W. S.;Angga, S.H.;Kwon, S. H.;Kwon, S. G.;Park, J. M.;Kim, J. S.;Chung, S. W.;Chae, Y. H.
    • Tribology and Lubricants
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    • v.31 no.2
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    • pp.50-55
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    • 2015
  • This study investigates the effects of a pattern of 200 μm dimples in a hexagonal array on tribological characteristics. A textured surface might reduce the friction coefficient and wear caused by third-body abrasion and thus improve the tribological performance. There are three friction conditions based on the Stribeck curve: boundary friction, mixed friction, and fluid friction conditions. In this experiment, we investigate the friction characteristics by carrying out the friction tests at sliding speeds ranging from 0.06 to 0.34 m/s and normal load ranging from 10 to 100 N. We create dimple surfaces for texturing by using the photolithography method. There are three kinds of specimens with different dimple densities ranging from 10% to 30%. The dimple density on the surface area is the one of the important factors affecting friction characteristics. Friction coefficient generally decreases with an increase in the velocity and load, indicating that the lubrication regime changes depending on the load and velocity. The fluid friction regime is fully developed, as indicated by the duty number graph. Fluid friction occurs at a velocity of 0.14-0.26 m/s. The best performance is seen at 10% dimple density and 200 μm dimple circle in the hexagonal array.

Friction Behavior of Oil-enriched Nanoporous Anodic Aluminum Oxide Film (오일 함침된 나노 기공 산화알루미늄 필름의 마찰 거동)

  • Kim, Hyo-Sang;Kim, Dae-Hyun;Hahn, Jun-Hee;Ahn, Hyo-Sok
    • Tribology and Lubricants
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    • v.27 no.4
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    • pp.193-197
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    • 2011
  • Friction behavior of nanoporous anodic aluminum oxide(AAO) film was investigated. A 60 ${\mu}m$ thick AAO film having nanopores of 45 nm diameter with 105 nm interpore-diatance was fabricated by mild anodization process. The AAO film was then saturated with paraffinic oil. Reciprocating ball-on-flat sliding friction tests using 1 mm diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 N to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient significantly increased with the increase of load. The boundary lubrication layer of paraffinic oil contributed to the lower friction at relatively low load (0.1 N), but it is less effective at high load (1 N). Plastic deformed layer patches were formed on the worn surface of oil-enriched AAO at relatively low load (0.1 N) without evidence of tribochemical reaction. On the other hand, thick tribolayers were formed on the worn surface of both oil-enriched and as-prepared AAO at relatively high load (1 N) due to tribochemical reaction and material transfer.

CFD Analysis of Trap Effect of Groove in Lubricating Systems: Part I - Variation in Cross-Sectional Shape of Groove (그루브의 Trap 효과에 대한 CFD 해석: 제 1부 − 그루브 단면 형상의 변화)

  • Hong, Sung-Ho
    • Tribology and Lubricants
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    • v.32 no.3
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    • pp.101-105
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    • 2016
  • Trap effect of groove is evaluated in a lubricating system using computational fluid dynamics (CFD) analysis. The simulation is based on the standard k-ε turbulence model and the discrete phase model (DPM) using a commercial CFD code FLUENT. The simulation results are also capable of showing the particle trajectories in flow field. Computational domain is meshed using the GAMBIT pre-processor. The various grooves are applied in order to improve lubrication characteristics such as reduction of friction loss, increase in load carrying capacity, and trapping of the wear particles. Trap effect of groove is investigated with variations in cross-sectional shape and Reynolds number in this research. Various cross-sectional shapes of groove (rectangular, triangle, U shaped, trapezoid, elliptical shapes) are considered to evaluate the trap effect in simplified two-dimensional sliding bearing. The particles are assumed to steel, and defined a single particle injection condition in various positions. The “reflect” boundary condition for discrete phase is applied to the wall boundary, and the “escape” boundary condition to “pressure inlet” and “pressure outlet” conditions. The streamlines are compared with particles trajectories in the groove. From the results of numerical analysis in the study, it is found that the cross-sectional shapes favorable to the creation of vortex and small eddy current are effective in terms of particle trapping effect. Moreover, it is found that the Reynolds number has a strong influence on the pattern of vortex or small eddy current in the groove, and that the pattern of the vortex or small eddy current affects the trap effect of the groove.

Improvement of Tribological Characteristics of Multi-Scale Laser-Textured Surface in terms of Lubrication Regime (윤활영역에서 멀티크기 Laser Surface Texturing 효과)

  • Kim, Jong-Hyoung;Choi, Si Geun;Segu, Dawit Zenebe;Jung, Yong-Sub;Kim, Seock-Sam
    • Tribology and Lubricants
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    • v.30 no.1
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    • pp.59-63
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    • 2014
  • Laser Surface Texturing(LST) is a surface engineering process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsated laser beam is used to create arranged dimples on a surface by a material ablation process, which can improve such as load capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect of multi-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI 52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples with some specific formula arrays were fabricated by combining circles, ellipses and the laser ablation process. The tribological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubrication and the results compared with that of the non-textured surface. Through an increase in sliding speed, the beneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower friction coefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.

Development of Solid Lubricants for Oil-less Bush (오일리스 부시용 고체윤활제 개발)

  • Kong, Hosung;Han, Hung-Gu;Kim, Jin Uk;Kim, Kyoung Seok;Park, Jong Sik
    • Tribology and Lubricants
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    • v.35 no.2
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    • pp.87-93
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    • 2019
  • This work aims to develop a dry lubricant for oilless bush, especially a solid lubricant, thereby creating a coating method with improved properties of anti-friction and load-carrying capacity without oil lubrication. In this work, spherical-shaped powders of thermosetting resin such as polyimide (PI) are mixed with a binder matrix obtained by mixing a fluorocarbon compound resin such as Polytetrafluoroethylene (PTFE) or Ethylene tetra fluoro ethylene (ETFE) with itself or with a non-fluorocarbon thermoplastic resin such as Polyether ether ketone (PEEK). And these dry lubricant mixtures are thickly coated (200-300 mm in the thickness) on the inner surface of the bush by using a wet-typed air-spray deposition method. It was found that the load-carrying capacity of the solid lubricant for excavator bush (60 mm in diameter) that operates under a high load condition (at 40 MPa) is greatly improved owing to the spherical-shaped powders of thermosetting resin. In addition, the coefficient of friction at the sliding surface is also reduced less than 0.1. Thick coating also lowers the contact stress at the edge of a bush that results in better tribological performances. The result suggests that the lubrication performance and durability life of the bush can be remarkably improved even without lubrication (oil or grease).

Study on Optimal Design and Analysis of Worm Gear and Casing of 5 Ton Class Worm Gear Reducer (5톤급 웜기어 감속기의 워엄기어와 케이싱의 최적설계 및 해석에 관한 연구)

  • Cho, Seong Hyun;Jeon, Chang Min;Qin, Zheon;Kim, Dongseon;Lyu, Sung-Ki
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.18 no.12
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    • pp.15-21
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    • 2019
  • The worm reducer is capable of quadrature power transmission when the shafts are disposed at right angles to each other. Since a large reduction ratio can be obtained of up to approximately 1/100 and a sliding movement is performed during operation compared with other gears, the noise and vibration are small, and there is the advantage that reverse rotation can be prevented. On the other hand, severe wear and damage are displayed on the gear and worm tooth surface, and many defects, such as intense heat generation of the reducer, occur. In the reducer case, the four-piece casing method was selected to solve the problems of heat generation, transmission efficiency, and assemblability. In this paper, we analyzed the problems of the worm and worm wheel (the core parts of a 5-Ton worm reducer) and casing through these methods and researched how to solve them.

A analysis of friction relation between tennis outsole and tennis playing surfaces (테니스화겉창과 테니스 스포츠바닥재간의 마찰관계상관 분석)

  • Kim, Jung-Tae
    • Korean Journal of Sport Biomechanics
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    • v.12 no.2
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    • pp.361-380
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    • 2002
  • The purposes of this study were to a analysis of friction relation between tennis outsole and tennis playing surfaces. Tennis footwear is an important component of tennis game equipment. It can support or damage players performance and comfort. Most importantly athletic shoes protect the foot preventing abrasions and injuries. Footwear stability in court sports like tennis is incredibly important since it is estimated that as many as 45% of all lower extremity injuries occur in the foot and ankle. The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. The friction force opposes the motion of the object. Friction results when two surfaces are pressed together closely, causing attractive intermolecular forces between the molecules of the two different surfaces. The outsole provides traction and reduces wear on the midsole. Today's outsoles address sport specific movements (running versus pivoting) and playing surface types. Different areas of the outsole are designed for the distinct frictional needs of specific movements. Traction created by the friction between the outsole and the surface allows the shoe to grip the surface. As surfaces, conditions and player motion change, traction may need to vary. An athletic shoe needs to grip well when running but not when pivoting. Laboratory tests have demonstrated force reductions compared to impact on concrete. There is a correlation between pain, injury and surface hardness. These are a variety of traction patterns on the soles of athletic shoes. Traction like any other shoe characteristic must be commensurate and balanced with the sport. The equal and opposite force does not necessarily travel back up your leg. The surface itself absorbs a portion of the force converting it to other forms of energy. Subsequently, tennis court surfaces are rated not only for pace but also for the percentage of force reduction.