• 한국공작기계학회논문집
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• 제17권2호
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• pp.65-70
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• 2008

This study deals with the friction welding of SKH55 and SM45C; The friction time was variable conditions under the conditions of spindle revolution 2,000rpm, friction pressure of 190MPa, upset pressure of 270MPa and upset time of 2.0 seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests were studied, and so the results were as follows. 1. When the friction time is 1.0 seconds, the tensile strength of friction welds was 926MPa, which is around as much as 84% of the tensile strength of base metal(SKH55), the bending strength of friction welds was 1,542MPa, which is around as much as 80% of the bending strength of base metal(SKH55), the shear strength of friction welds was 519MPa, which is around as much as 70% of the shear strength of base metal(SKH55). 2 According to the hardness test, the hardness distribution of the weld interface was formed from 964Hv to 254Hv. HAZ(Heat Affected Zone) was formed from the weld interface to 1.5mm of SKH55 and 2mm of SM45C.

• 한국도로학회논문집
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• 제12권3호
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• pp.131-137
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• 2010

본 논문에서는 국내 공항 활주로에 적합한 마찰계수 측정 및 고무 퇴적물 제거에 대한 합리적 기준 개발을 위해 관련 해외 기준 및 연구결과에 관한 문헌을 조사하였다. 그리고 2007년 8월부터 2009년 7월까지ASFT(Airport Surface Friction Tester)장비를 이용하여 인천국제공항 활주로의 마찰계수를 측정하고 항공기 집중 착륙 지점에 대한 분석을 실시하였다. 타이어 고무의 퇴적 및 제거에 따른 마찰계수의 변화를 분석하였고 이에 미치는 계절적 영향을 포장 형식별로 조사하였다. 고무 퇴적물 제거 작업을 주기적으로 수행해도 활주로 표면의 마찰계수는 장기적으로 시간에 따라 점차 감소되는 것으로 확인되었다. 여름철 마찰계수의 변화가 다른 계절에 비해 컸으며 아스팔트 포장이 콘크리트 포장보다 계절적 영향에 민감했다. 매크로한 표면조직을 갖는 아스팔트 포장의 마찰계수가 마이크로한 표면조직을 갖는 재령 초기 콘크리트 포장의 마찰계수보다 큰 것으로 나타났다. 타이어 고무의 퇴적 및 제거에 따른 마찰계수의 변화도 아스팔트 포장에서 더 큰 것으로 확인되었다.

• Tribology and Lubricants
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• 제31권2호
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• pp.42-49
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• 2015

Because of the growing need for high-speed transport options such as trains and aircraft, there is increasing demand for technology related to high-speed trains. Among them, braking systems are important in high-speed trains in terms of reliability. Especially, the disk brake system, in use in most high-speed trains, transforms kinetic energy into thermal energy and noise. Therefore, the material properties of both the friction materials and disks are expected to influence the tribological characteristics. In this paper, the tribological characteristics depend on the hardness of the brake disks between the Cu-based sintered metallic friction material and the heat-treated heat-resisting steel disks. A lab-scale dynamometer used to perform braking tests at a variety of braking speeds using dry conditions. The test results revealed that the hardness of the disks affects the friction coefficients, friction stabilities, and wear rates. Thus, the brake system using the heat-resisting steel disk requires proper heat-treatment. These differences are considered to be caused by the change in tribological mechanisms and the generation of an oxide layer on the friction surfaces. The oxide layers on the friction surfaces are confirmed to Fe₂O₃ by x-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) analysis.

• Journal of Mechanical Science and Technology
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• 제20권6호
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• pp.738-747
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• 2006

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-on-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 mm, 0.5 mm and 1 mm were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer In-terestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly Influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains.

• 한국산업융합학회 논문집
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• 제23권6_2호
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• pp.917-926
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• 2020

Friction mechanisms is a very important role in the industrial machinery. However, many experiments have been conducted to reduce the loss of energy resources and parts used due to friction because the friction force adversely affects parts, efficiency, noise, and the like of the power unit. Therefore, in this study, the friction coefficient according to the characteristics of the lubricant was measured to find out which Grease Lubricant maintains the low friction coefficient without being most affected by external conditions. A total of five grease lubricants were tested in this study: GHP CAL 301, GHP EP 2, GHP KG 10, GHP HPG 2, and GHP HTG 2. And the friction coefficient was conducted by changing the load conditions (2, 4, 6, 8, 10N) and rotational speed (24, 48, 67, 86, 105, 124, 143, 162vrpm) using a pin-on-disk wear test system. Also, duty number were calculated. As a result, it was confirmed that in all grease lubricants, the speed did not significantly affect the friction coefficient, and it was confirmed that in all lubricants, the size of the friction coefficient decreased as the load increased from a small load to a large load. In addition, it was determined from the experimental results that GHP EP 2 is the most suitable as a grease lubricant and GHP CAL 301 is not the most suitable.

• Tribology and Lubricants
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• 제37권3호
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• pp.106-111
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• 2021

There are several studies on reducing the friction that occurs on the relative sliding contact surface of moving parts under extreme environments. In particular, a solid lubricated bearing is studied to solve the tribological problem with friction reduction and durability parts using solid lubricants (lead or silver) in a vacuum atmosphere. Galinstan is mainly used as a liquid metal lubricant, but it is inevitable to have limited tribological applications owing to its high coefficient of friction. Many researchers work on surface texturing for surface modification and precision processing methods. To increase durability and low friction, DLC coating with hydrophobicity is applied on the contact surface texture. Therefore, using an untextured specimen, a dimple specimen, and a DLC-coated dimple specimen under liquid metal lubrication, this paper presents the following experimental sliding friction characteristics in the sliding friction test. 1) The average coefficient of friction of the DLC-coated dimple specimen and dimple specimen are lower compared to that of a non-patterned specimen. 2) In the DLC-coated dimple specimens, the average coefficient of friction changes according to the change in the dimple density. 3) DLC-coated dimple specimens with a density of 12.5 have the lowest average coefficient of friction under 41.6 N of normal load and 143.3 RPM.

• 한국전산구조공학회논문집
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• 제34권4호
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• pp.213-219
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• 2021

구조물을 지진 위험으로부터 완화시키기 위한 마찰면진장치의 상용화된 마찰재료 중 폴리테트라플루오로에틸렌(polytetrafluoroethylene, PTFE)은 내화학성과 마찰성능이 우수하다. 그러나 PTFE는 상대적으로 낮은 내마모성을 가지므로 경제적인 마찰재료이며 산화마그네슘(oxide magnesium, MgO)으로 내마모성을 증가시킨 개선된 폴리비닐리덴 플루오라이드(polyvinylidene fluoride, PVDF)를 PTFE의 대안으로 제안하였다. 개발된 PVDF/MgO 마찰재를 이용하여 실험을 통해 마찰성능을 측정하였으며 PTFE의 마찰성능과 비교하였다. 그리고 측정된 마찰계수를 이용하여 마찰면진장치를 설계하였다. 마찰면진장치의 성능은 교량의 비선형 시간이력 해석을 통해 확인하였고, 이를 통해 마찰면진장치의 마찰재료로 PTFE를 대체하여 PVDF/MgO를 사용하는 것에 대한 타당성을 평가하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1934-1937
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• 1999

A copper-tungsten sintered alloy(Cu-W) has been friction-welded to a tough pitch copper (Cu) in order to investigate friction weldability. The tensile strength of the friction welded joint was increased up to 87% of the Cu base metal under the condition of friction time 1.0 see, friction pressure 40MPa and upset pressure 100MPa, upset time 5.0 sec. And it is related to upset pressure rather than friction time. Mixed layer was formed in the Cu adjacent weld interface and W particles which were included in mixed layer could induce fracture in the Cu adjacent to the weld interface. Thickness of mixed layer was reduced as upset pressure increase.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.319-320
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• 2002

Numerical simulation of chip formation during high speed machining requires knowing the friction at tool/chip interface. This parameter is hardly identified and generally the loadings (temperature, force) during the identification are not similar to those encountered during machining. Thus, Coulomb friction identified with pin-on-disc device is often used to conduct numerical simulation. The used of this technique cannot leads to good numerical results of chip formation compared to the experimental tests especially in the case of low uncut chip thickness. In this contribution, we propose a new method to evaluate the friction at tool/chip interface. In fact several Coulomb friction parameters are identified corresponding to several parts of the cutting tool. Experimental tests have been conducted allowed us to determinate both the level and the distribution of the Coulomb friction. Experimental results are also compared to the results of orthogonal cutting simulation. We show that this technique allows predicting accuracy results of chip formation.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.233-234
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• 2002

Diamond composites hold promise as a tribological material because of low friction and high wear resistance. We studied friction and wear of polyimide-20vol% PTFE-diamond composites in open air at room temperature, focusing on the effects of diamond size, and diamond content, sliding conditions, and mating material. Friction coefficient and wear tend to Increase with increasing diamond size and content. Composites of appropriate diamond size and content showed a friction coefficient below 0.1 and specific wear of $10^{-7}\;mm^3/Nm$. Friction and wear of composites sliding against stainless steel were higher than those of Al_2O_3$ an increase that became increasingly not able with increasing diamond size.