• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.105-111
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• 2003

The valve train system of engines has long been a sensitive area with respect to wear performance because of the high contact loads and surface sliding speeds encountered. In particular, wear problems of load-carrying components in relative motion, such as cam and tappet in valve train system have made troubles. To overcome these problems, combination of proper materials is important, as well as selecting of high wear performance materials. This paper presents the experimental result of friction and wear properties of ca/tappet materials. To investigate friction and wear properties for several combinations of materials, using commonplace tribometer(Plint 77, reciprocating type), we make a selection of a optimum material combination.

• 한국자동차공학회논문집
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• 제13권5호
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• pp.104-111
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• 2005

With increasing use of SUH35/SUH3 dissimilar materials for automotive engine valves, it is required that stress singularities under residual stress on an interface for friction welded dissimilar materials analyzed to establish strength evaluation. The stress singularity $index{\lambda}$ and stress singularities $factor{\Gamma}$ were calculated from using the results of stress analysis to consider residual stress and loads. The stress singularities on variations for shapes and thickness of welded flashes were analyzed and discussed. This paper suggested that the strength evaluation by using the stress singularity factors as fracture parameters, considering the stress singularity on an interface edge of friction welded dissimilar materials will be useful.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.226-234
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• 2002

A systematic study of the role of transfer films on friction properties was performed with various temperatures in the brake system. An NAO friction material specimens containing 9 ingredients were tested using a pad-on-disk type friction tester A new method of measuring the transfer film thickness was developed by considering the electrical resistance of the transfer film using a 4-point probe technique. The properties of transfer film such as surface morphology and film distribution vaied according to the relative amount of graphite and magnesium oxide. By using SEM, it was possible to obtain information about the chemical composition of the transfer film. Results showed that there detected a threshold value of the relative amount of a two active materials to maintain a certiain thickness of a transfer film. Results also showed that formation of friction layer generated on the friction surface was strongly affected by chemical action of two ingredients during sliding due to chemical reaction of solid lubricants at different interface temperature. The results suggested that no apparent relationship between transfer film thickness and the average friction coefficient was founded and friction characteristics were affected more by the property of the solid lubricant and abrasive in the material.

• Tribology and Lubricants
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• 제23권1호
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• pp.9-13
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• 2007

Despite numerous researches on atomic-scale friction have been carried out for understanding the origin of friction, lots of questions about sliding friction still remain. It is known that friction at atomic-scale always shows unique phenomena called 'stick-slips' which reflect atomic lattice of a scanned surface. In this work, experimental study on the effects of system stiffnesses and load on the atomic-scale stick-slip friction of graphite was performed by using an Atomic Force Microscope and various cantilevers/tips. The objective of this research is to figure out the dependency of atomic-scale friction on the nanomechanical properties in sliding contact such as load, stiffness and contact materials systematically. From this work, the experimental observation of transitions in atomic-scale friction from smooth sliding to multiple stick-slips in air was first made, according to the lateral cantilever stiffness and applied normal load. The superlubricity of graphite could be verified from friction vs. load experiments. Based on the results, the relationship between the stickslip behaviors and contact stiffness was carefully discussed in this work. The results or this work indicate that the atomic-scale stick-slip behaviors can be controlled by adjusting the system stiffnesses and contact materials.

• 소성∙가공
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• 제24권6호
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• pp.381-386
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• 2015

Recently, high-strength-steel sheets have been used extensively for increasing fuel-efficiency and stability in automobiles. A study on the characteristics regarding friction factors is required because high-strength-steel sheets have higher contact pressure at the tool interface as compared to low-strength steel sheets. For the current study, a sheet friction test was used to examine the influence of several factors on friction. The friction tests were performed on two types of sheet steels (SPFC590 and SPFC980) to obtain friction coefficients as a function of contact pressure, surface roughness, lubricant viscosity, and speed. Based on the experimental results for SPFC590 and SPFC980, the friction coefficient decreased with increasing contact pressure, but the friction coefficient increased with increasing surface roughness. Also, the friction coefficient decreased with increasing lubricant viscosity and decreasing speed.

• 한국재료학회지
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• 제27권5호
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• pp.276-280
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• 2017

This study was carried out to evaluate the developed microstructures and mechanical properties of friction welded A6063 alloy. For this work, specimens were prepared at a size of 12 mm ${\O}{\times}80mm$, and friction welding was carried out at a rotation speed of 2,000 RPM, friction pressure of $12kgf/cm^2$ and upset pressure of $25kgf/cm^2$. To perform an analysis of the grain boundary characteristic distributions, such as the grain size, orientation and misorientation angle distributions, the electron back-scattering diffraction method was used. In addition, in order to identify the dispersed intermetallic compounds of the base and welded materials, transmission electron microscopy was used. The experimental results found that the application of friction welding on A6063 led to significant grain refinement of the welded zone relative to that of the base material. Besides this, intermetallic compounds such as AlMnSi and $Al_2Cu$ were found to be dispersed with more refined size relative to that of the base material. This formation retains the mechanical properties of the welds, which results in the fracture aspect at the base material zone. Therefore, based on the developed microstructures and mechanical properties, the application of friction welding on A6063 could be used to obtain a sound weld zone.

• Journal of Welding and Joining
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• 제31권2호
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• pp.26-29
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• 2013

마찰교반용접(FSW) 및 마찰교반처리(FSP) 기술 관련 국제 심포지움인 'Friction Stir Welding & Processing VII'에서 발표된 연구논문의 내용을 토대로 아래와 같이 최신 연구개발 동향을 정리하였다. ${\cdot}$ 알루미늄합금과 마그네슘합금의 경량금속에 대한 마찰교반용접이 주류를 이루었던 과거와 달리 최근에는 구조용 연강, 고강도강, 초내열합금 및 타이타늄 합금 등의 고융점 금속재료에 대한 마찰교반용접 공정기술 및 툴의 개발이 수행되고 있다. ${\cdot}$ 주조재 표면 조직의 균질화 및 나노 사이즈의 초미세 결정립 조직을 얻기 위한 개질(改質)을 비롯하여 CNTs 및 Graphene 등의 첨단 탄소소재를 판재의 표면에 코팅 또는 판재 내부에 분산시켜 금속기 나노탄소복합재(MMNCC: Metal Matrix Nano Carbon Composites)의 제조 및 기계적 특성 향상을 목적으로 하는 FSP 관련 연구가 다각적으로 수행되고 있다. ${\cdot}$ 마찰교반용접 공정 중의 접합부의 형성 및 금속유동(Metal flow)에 대한 모델링(Modeling) 관련 연구가 다수 진행되고 있으며, 수학적 해석 및 실시간 모니터링을 통한 연구가 의욕적으로 진행되고 있다.

• 소성∙가공
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• 제23권7호
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• pp.413-418
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• 2014

The current study presents experimental and numerical results on the effect of ultrasonic vibrations on a cylindrical cup drawing of a cold rolled steel sheet(SPCC). An experimental apparatus, which can superimpose high frequency oscillations during deep drawing, was constructed by installing on the tooling ultrasonic vibration generators consisting of a piezoelectric transducer and a resonator. Conventional and vibration-assisted cylindrical deep drawing tests were conducted for various drawing ratios, and the limiting drawing ratios(LDR) for both methods were compared. To evaluate quantitatively the contribution from the ultrasonic vibrations to the reduction of friction between tools and material finite element analyses were conducted. Through a series of parametric analyses, the friction coefficients, which minimized the differences of punch load data between the experiments and simulations, were determined. The results show that the application of ultrasonic vibration effectively improves the LDR by reducing the friction between the tools and the material.

• 한국전산구조공학회논문집
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• 제30권2호
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• pp.95-102
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• 2017

이 논문에서는 LNG 탱크를 지진으로부터 격리시키는 면진장치의 일종인 마찰진자시스템(FPS)의 성능변화에 따른 구조물 응답 및 지진취약도를 분석하였다. 마찰진자시스템(FPS)에 사용되는 마찰재 시편을 PVDF와 $TiO_2$의 배합비율에 따라 제작하였다. 제작한 마찰재 시편의 물성을 면진받침에 적용하여 구조물의 가속도 응답 및 외조 콘크리트의 하부 모멘트에 대하여 분석하고 각각의 한계상태에 대해 지진취약도를 분석하였다. 구조물의 지진취약도 분석을 통한 최적의 배합비를 가지는 마찰재 선정을 위해 각 한계상태에 따른 지진취약도 곡선의 가중치 설정 후 조합이 필요한 것을 확인하였다. 이를 통하여 다양한 구조물에 적용되는 마찰진자시스템의 요구 성능을 만족하는 최적의 마찰재 선정이 가능할 것으로 기대된다.

• Advances in materials Research
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• 제4권3호
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• pp.165-178
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• 2015

Friction coefficient of epoxy metal matrix composites were investigated. The main objective was to increase the friction coefficient through rubber sole sliding against the epoxy floor coating providing appropriate level of resistance. This was to avoid the excessive movement and slip accidents. Epoxy metal matrix composites were reinforced by different copper wire diameters. The epoxy metal matrix composites were experimentally conducted at different conditions namely dry, water and detergent wetted sliding, were the friction coefficient increased as the number of wires increased. When the wires were closer to the sliding surface, the friction coefficient was found to increase. The friction coefficient was found to increase with the increase of the copper wire diameter in epoxy metal matrix composites. This behavior was attributed to the fact that as the diameter and the number of wires increased, the intensity of the electric field, generated from electric static charge increased causing an adhesion increase between the two sliding surfaces. At water wetted sliding conditions, the effect of changing number of wires on friction coefficient was less than the effect of wire diameter. The presence of water and detergent on the sliding surfaces decreased friction coefficient compared to the dry sliding. When the surfaces were detergent wetted, the friction coefficient values were found to be lower than that observed when sliding in water or dry condition.