• Tribology and Lubricants
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• 제10권3호
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• pp.29-38
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• 1994

The friction and wear of mild steel at dry sliding surfaces under different vacuum conditions have been investigated to understand the wear mechanisms. For the test, a ball-ondisk typed wear-rig has been built and implemented, allowing control of sliding speed, load and vacuum. Results show that, at a high sliding velocity, friction of low carbon steel (SS41) under a high vacuum is much higher than that of ambient condition and wear is much severer. It is due to lack of effective oxidation film formation on which steel surfaces could protect themselves against the severe wear. It has been shown, however, that there is a critical regime with contact conditions (at a low sliding velocity, a low load, and under a medium vacuum) at which effective, protective films of low carbon steel have been built on the surfaces in a friction process with a self-regulating way, resulting in both very low coefficients of friction (about 0.3) and mild wear. In order to investigate the protective films on steel surfaces, the worn surfaces and the wear debris have been experimentally analyzed with SEM, AES/SAM and XRD. A theoretical analysis of frictional heating at sliding surfaces, and an experimental analysis of the influence of oxidation wear under various vacuum conditions are described. The important variables on which self-formations of protective films at dry sliding surfaces depend, and the wear mechanisms are also investigated.

• 대한기계학회논문집A
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• 제29권6호
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• pp.860-875
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• 2005

A new meshfree method for the analysis of elasto-plastic deformations is presented. The method is based on the proposed first-order least-squares formulation, to which the moving least-squares approximation is applied. The least-squares formulation for the classical elasto-plasticity and its extension to an incrementally objective formulation for finite deformations are proposed. In the formulation, the equilibrium equation and flow rule are enforced in least-squares sense, while the hardening law and loading/unloading condition are enforced exactly at each integration point. The closest point projection method for the integration of rate-form constitutive equation is inherently involved in the formulation, and thus the radial-return mapping algorithm is not performed explicitly. Also the penalty schemes for the enforcement of the boundary and frictional contact conditions are devised. The main benefit of the proposed method is that any structure of cells is not used during the whole process of analysis. Through some numerical examples of metal forming processes, the validity and effectiveness of the method are presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.396-401
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• 2008

The disc-pad brake system is an important part of automobile safety system. During braking, the kinetic energy and potential energies of a moving vehicle are converted into the thermal energy through frictional heat between the brake disc and the pads. Most of the thermal energy dissipated through the brake disc. The temperature could be exceed the critical value for a given material, which leads to undesirable effects, such as the brake fade, premature wear, brake fluid vaporization, bearing failure, thermal cracks, and thermallyexcited vibration. The object of the present study is to investigate temperature field and temperature variation of brake disc and pad during single brake. The brake disc is decelerated at the initial speed with constant acceleration, until the disc comes to stop. The pad-disc brake assembly is built by 3D model with the appropriate boundary condition. In the simulation process, the mechanical loads are applied to the thermomechanical coupling analysis in order to simulate the process of heat produced by friction.

• 대한기계학회논문집
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• 제17권6호
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• pp.1441-1455
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• 1993

본 연구에서는 최신기법에 의해서 제조된 HIP제 질화규소와 지르코니아를 실험재료로 하여 무윤활하에서의 미끄럼마찰·마멸실험을 수행하여 마찰·마멸특성을 규명하고, SEM을 이용한 마멸면의 미시적 관찰을 통해서 세라믹의 마멸기구를 조사하 여 세라믹마멸기구의 마멸모델을 제시하고자 한다. 제시된 마멸모델에서 파괴역학을 도입하여 이론해석과 고찰을 수행하여 보다 실용적인 세라믹의 마멸율울 평가할 수 있 는 새로운 무차원 파라메터를 제안하고자 한다.

• Tribology and Lubricants
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• 제26권3호
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• pp.162-166
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• 2010

The purpose of this study is to show the friction and wear characteristics on the vapor deposited Tiseries coating layers on the SCM415 steel. In this research, frictional wear characteristic of coating materials such as TiN, TiCN, TiAlN was investigated under room temperature, normal air pressure and dry lubricating condition. Therefore this study carried out research on the friction coefficient, micro hardness(Hv), roughness, SEM on the vapor deposited coating layers on the SCM415 steel.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.368-375
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• 2009

This paper describes field installation and load test results performed for three types of micropiles in the process of developing a new micropiling method. Field tests were performed for two conventional types(i.e., micropile reinforced with steel bar and gravity grouting, micropile reinforced with steel bar and steel casing and gravity grouting) and a proposed type(i.e., micropile reinforced with hollow steel pipe wrapped with geotextile-pack and pressurized grouting). The load test results subjected to axial compression and tension and lateral loading conditions are described in this paper. The micropiles were exposed in the air in order to verify the installation quality and curing condition of grouting material via ground excavation. Axial compression and tension test results indicate that the new micropile type provide at least 40% higher bearing capacity than that of conventional types. Based on the examination of exposed piles, it is induced that the proposed method, packed micropile, provides better interlocking between grouts and surrounding soils and increases higher frictional resistance comparing to conventional types.

• 대한조선학회논문집
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• 제53권3호
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• pp.201-209
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• 2016

Supercavitation is a technology that reduces frictional resistance of an underwater vehicle by surrounding it with bubbles. Supercavity is divided into natural supercavity and ventilated supercavity which is formed by artificially supplying gas. Planing forces are present when a section of the underwater vehicle goes outside of the cavitation region in the supercavity condition. Planing often leads to an unstable flight because it acts vertically on the body suddenly. In this paper, a relationship between the ventilation rate and the cavitation number is determined. Based on the relationship, desired cavitation number which can avoid to planing is determined and then ventilation controller is designed. The performance of the ventilation controller is verified with a depth change controller using the cavitator. Simulation results show that the ventilation controller can minimize the planing force and moment.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.324-324
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• 2008

Piezoelectric ceramics is an active element that makes stator to vibrate to generate rotational force in ultrasonic motors. In drive of ultrasonic motors, many factors that affect to the resonance characteristics of piezoelectric ceramics exist. For example, those factors are bonding condition with elastic body, the magnitude of electric field, the normal force for frictional drive and the emission of heat due to vibration and friction and so on. Therefore, it is important to research the inclination of property variation of piezoelectric ceramics in circumstance that has complex elements. In this paper, we focused and analyzed the resonance characteristics of ultrasonic motor due to the magnitude of the driving voltage and normal force.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3728-3740
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• 1996

High-quality cups of deep drawing ratio of more than four cannot be simply drawn by conventional drawing and redrawing processes. In the present study, after the first deep drawing process, subsequent hydromechanical reverse redrawing with controlled radial pressure is employed. In order to increase the deep drawing ratio up to muchmore than four, the radial pressure should be controlled independently of the chamber pressure and thus an optimum forming condition can be found easily by varying the radial pressure. The process has been subjected to finite element analysis by using the rigid-platic material modeling considering all the frictional conditions induced by the hydrostatic pressure. In order to consider the pressure effect on the sheet, the pressure distributions on the flange part and the side wall part are calculated mumerically from simplified Navier-stokes equation. The comparison of the computation with the experiment has shown that the finite element modeling can be conveniently emplyed for the design of the process with reliability from the viewpoint of formability.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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• pp.297-301
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• 2002

High-speed machining generates concenter thermal/frictional damage at the cutting ed rapidly decreases the tool life. This paper I at determining the effect of cutter orienter the cutting environment on tool life, tool mechanism when down milling. In this paper, experiments were carried out in various tool and cutting environments, such as dry, wet compressed chilled air, tool life were measu evaluate machinability in high-speed milli difficult-to-cut material and die steel, Tool measured in horizontal upwards, horiz downwards, vertical upwards and vert downwards. In addition, tool life was measur dry, wet and compressed chilled air. For this a compressed chi1led-air system was manufact The results show that a horizontal cutter ori provided a longer tool life than a vertical orientation. With respect to the cutting envi compressed chilled air increased tool life. H the wet condition decreased tool life due thermal shock caused by excessive cooling high-speed mill ins and the compressed chilled had little effect.