• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.449-455
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• 2016

This study provides the finite-element (FE) squeal-model predicting friction-induced noise with respect to several friction materials that have different friction characteristics. The friction curve and the corresponding friction noise were measured for four friction materials (Cu, Ni, Al, Mg) using the pin-on-disk and reciprocating friction system. The slope of the friction curve linearized at the sliding velocity was applied to the FE model. The unstable modes in the complex eigenvalue analysis were shown to correspond to the squeal frequencies that existed in the experiment.

• Water for future
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• v.27 no.1
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• pp.101-109
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• 1994

Characteristics of the vortex structure and the secondary scour at downstream part of the hydraulic structure such as drainage sluice or spillway ere studied. Mean shear velocity in the scour hole could be derived by the theory of energy conservation and the amount of a vortex erosion could be obtained using entrainment equation for given value of a shear velocity. Comparison of erosion rates with others showed a large value at low shear velocity due to the continuous and strong upward flow of the macroturbulence different from the conventional vortex formed in the lee-side of a sand ripple. For a design purpose, if the flow depth at the end of an apron and the properties of bed material are given, the amount of vortex erosion can be known.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.103.1-103.1
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• 2012

본 연구는 차량경량화를 위하여 높은 인장강도와 우수한 인성을 가지는 590MPa급 이상조직강(Dual phase steel)을 이용하여 1991년 TWI(The Welding Institute)에서 개발된 마찰교반접합을 적용하여 접합을 실시하였다. 접합의 공정조건으로 툴의 회전속도는 250~350 RPM, 접합속도로는 50~350 mm/min로 겹치기접합을 실시하였다. 접합에서 사용된 툴은 Megastir에서 제작한 고융점마찰교반접합용 툴인 PCBN(Q-60)을 이용하였고 연구에 사용된 DP590은 포스코(POSCO)에서 제작된 1.4t(mm) 두께인 AHSS(advanced high strength steels)을 사용하였다. 모재인 DP590과 접합체의 미세조직은 광학현미경과 주사전자현미경을 이용하여 관찰하였으며 기계적 특성은 경도시험과 인장시험을 실시하여 조사하였다. 경도의 분포는 모재에서 약 220~230Hv이며 TMAZ부분에서 상승하기 시작하여 접합부에서 약 320Hv까지 상승하는 경향을 보였으며 인장시험 결과 접합속도 100~200 mm/min에서는 모든 시편이 모재에서 파단되어지는 것을 확인할 수 있었다. 위와 같은 결과 300~350 RPM, 100~200 mm/min의 공정조건에서는 접합이 성공적으로 이루어졌으며 차량경량화에 적용이 가능하다고 판단되어진다.

• Tribology and Lubricants
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• v.3 no.2
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• pp.64-67
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• 1987

미끄럼 운동에 의하여 미세한 시일링 간극에 열이 발생할 때 어떠한 빠르기로 발생된 열이 재질 내부로 전파되는가를 속도의 개념으로 이론적 해석을 하였다. 발생된 마찰열이 시일재질 내부로 전파되는 속도는 불안정한 온도의 파장에 의하여 커다란 영향을 받고 있다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1991.11a
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• pp.29-33
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• 1991

상업성장과 더불어 국내 자동차 산업이 급속도로 발전하고 있는 것이 현실이다. 이와 관련하여 내연기간의 연구 및 개발 회상에 대한 요구가 그 어느때보다도 절실한 시점에 와잇는것이 우리의 실정이다. 현재 내연기관에 있어서의 연구개발의 최대목적은 기관의 성능회상에 있다. 이러한 결과를 얻기 위해서는 여러가지 방법이 있으나 그 운동부분에서 마찰손시를 적게 하기 위한 노력을 경주하여야 함은 말할나위가 없다. 특히 자동차용 engine은 실린더의 크기가 작고 슬라이딩면의 며적이 비교적 크며, 저출력에서의 사용 빈도가 크기 때문에 마찰 손시이 차지하는 비율이 높다. Engine이 마찰 손실은 저부하 일수록 손실이 크며 이부분에서의 최대 손실은 engine 전체 손실의 약 50%까지 도달하고, 그중에서 마찰 손시의 30-50%를 engine의 piston ring과 cylinder 사이의 마찰력이 차지하는 것으로 알려지고 있다.

• Journal of the Korean Society for Railway
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• v.11 no.2
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• pp.188-194
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• 2008

Brake disks for rolling stock are exposed to thermal fatigue during braking, and thermal cracks occur on surface of disks. Thermal cracks can cause serious accidents, deterioration of braking performance and increase of maintenance cost due to frequent exchange of friction materials. In this study, candidate materials with high-heat resistance were selected by searching the literature. By using cast specimens made of the candidate materials, chemical composition, crystal structure and graphite type were analyzed. In addition, friction coefficient and wear were measured and compared with values for the disk material in service. As a result, it was shown that the NiCrMo has highest tensile strength and lowest friction coefficient and the disk material in service has the most stable friction characteristics.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.2
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• pp.13-22
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• 1998

This paper summarizes a study on the application of the friction pendulum system in bridge seismic isolation. Shaking table tests have been carried out on a model structure isolated with F.P.S and the obtained structural responses are compared to those of non-isolated. It can be concluded the F.P.S increases the earthquake resistance capacity of the isolated structure. It is also found that the stiffness of bearing, being controlled by the radius of curvature of the spherical sliding interface, is unaffected by the amplitude of the input excitation. Furthermore, the coefficient of sliding friction is velocity dependent so that in weak excitation the sliding velocity is low and, accordingly, the mobilized friction force is less than the one mobilized in strong excitation. Also, the frictional properties of the bearings remain markedly stable after extensive testing, and the permanent displacements are small and not cumulative in successive earthquakes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.513-518
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• 2019

Friction Stir Welding is a welding technique for metal materials that utilizes the heat generated by friction between the material to be welded and the welding tool that rotates at high speed. In this study, a numerical analysis method was used to analyze the change in the internal temperature of the welded material during friction stir welding. As the welding target material, AZ31 magnesium alloy was applied and the welding phenomenon was considered a flow characteristic, in which a melting-pool was formed. FLUENT was used as the numerical tool to perform the flow analysis. For flow analysis of the welding process, the welding material was assumed to be a high viscosity Newtonian fluid, and the boundary condition of the welding tool and the material was considered to be the condition that friction and slippage occur simultaneously. Analyses were carried out for various rotational speeds and the translational moving speed of the welding tool as variables. The analysis results showed that the higher the rotational speed of the welding tool and the slower the welding tool movement speed, the higher the maximum temperature in the material increases. Moreover, the difference in the rotational speed of the welding tool has a greater effect on the temperature change.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.39-53
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• 2018

Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

• Tunnel and Underground Space
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• v.15 no.4 s.57
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• pp.305-315
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• 2005

DDA (Discontinuous Deformation Anlaysis) is one of the latest numerical analysis which has merits of both FEM and DEM. In this research a new edge-to-edge contact algorithm was applied on DDA. With adoption of new edge-to-edge contact state definition, sub-algorithm was improved about open-close iteration, contact state judge, contact detecting, and friction forces acting on joints. Newly applied DDA was verified based on two different cases. The DDA results show good agreement with numerically predicted one.