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임충환(Lim Choong-Hwan),구병춘(Goo Byeong-Choon) 한국철도학회 2008 한국철도학회 학술발표대회논문집 Vol.- No.-
In the braking of a railroad car, mechanical brake systems using wheel tread and brake disk are applied as well as electrical brake systems by regenerator and rheostat. It is very important to consider the frictional characteristic because kinetic energy of the vehicle is dissipated as converted thermal energy through friction between disk and brake pad during disk braking. A friction coefficient and wear characteristic are decided from the interrelationship of disk and friction material in the disk brake system. Lab-scale dynamometer test on developed brake disk materials for increasing heat resistance was performed in this study. Each candidate material was tested at various braking speeds and pressures and we obtained the friction coefficient and wear characteristic. And we executed comparative evaluation of the result from the test.
임충환(Choong-Hwan Lim),구병춘(Byeong-Choon Goo) 한국철도학회 2010 한국철도학회 학술발표대회논문집 Vol.2010 No.7
During braking of railway vehicles the repetitive thermal shock leads to thermal cracks on disc surface, and the lifetime of brake disc is dependent on the number of trimming works for removing these thermal cracks. Many tries for development of high heat resistant brake disc to extend the disc life and to warrant reliable braking performance has been continued. In present study, we carry out the computational fatigue analysis for thermal fatigue test in three candidate materials which were made to develop new high heat resistant material. Using FEM, we simulate thermal fatigue test in three candidate materials and conventional disc material. We then estimate the number of cycle to thermal crack initiation based on data from mechanical fatigue tests, and the results are compared with each material. For each material, the correction factor for Nf-40 which is the number of cycles when crack over 40?㎛ was observed in thermal fatigue test is decided. From this study, we can verify the performance of thermal fatigue test system and suggest a qualitatively comparative method for heat resistance by FEM analysis of thermal shocking phenomenon.
A STUDY ON THE THERMAL FATIGUE TEST AND ANALYSIS METHOD FOR THE DEVELOPMENT OF BRAKE DISK MATERIALS
Choong Hwan Lim(임충환),Byeong Choon Goo(구병춘) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
In the disk braking of the railway trains, kinetic energy of the vehicles is converted into thermal energy by friction between a brake disk and the pad materials. This can be cause of the iterative thermal shock and generates thermal cracks on the brake disk surface. In this study, we show the comparative thermal fatigue test procedures and thermal crack analysis process to evaluate the thermal fatigue characteristics of candidate materials designed for development of heat-resistant brake disk material. We carried out tests on the conventional brake disk materials used for Saemaul and Mugunghwa trains, then we comparatively analyzed the thermal crack initiation and propagation on the surface of a specimen. A thermal fatigue test procedure and a crack analysis process were suggested to evaluate the heat resistance of the developed materials at later studies.
임충환(Choong-Hwan Lim),구병춘(Byeong-Choon Goo) 한국철도학회 2011 한국철도학회 학술발표대회논문집 Vol.2011 No.5
The high heat resistant material for brake disc is required for higher speed trains. Although Aluminum is very expensive, it which has high thermal conductivity and low density has been adapted to high performance light-weight brake disc. In this study, we carry out the thermal stress analysis for suggested shape of Al hybrid brake disc which was designed to meet the optimal point between a performance and economic side. And we compare the results from the analysis to results of conventional disc at the same braking speed. The result show that the temperature on braking surface of Al hybrid disc is lower than the temperature on conventional disc surface, whereas the maximum thermal stress is larger than stress on conventional disc.
임충환(Lim Choong-Hwan),구병춘(Goo Byeong-Choon) 한국철도학회 2008 한국철도학회 학술발표대회논문집 Vol.- No.-
In the braking of a railroad car, mechanical brake systems using wheel tread and brake disk are applied as well as electrical brake systems by regenerator and rheostat. During disk braking, kinetic energy of the vehicle is converted into thermal energy through friction between disk and brake pad. And it causes high temperature concentration and generates thermal crack on the brake disk surface. In this study, comparative test process for heat-resistance of candidate materials was designed for development of brake disk materials having high heat-resistance. We also verified the efficiency of the process by experiments using conventional brake disk materials.
구병춘(Byeong Choon Goo),임충환(Choong Hwan Lim) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.8
철도차량의 제동 디스크에 사용될 수 있는 주물재료 4 종에 대해 인장강도, 압축강도, 경도, 비열, 비중, 열전도도 등 여러 특성값을 측정하였다. Ni, Cr, Mo 의 조성비에 따라 인장강도, 압축강도, 경도 등을 조절할 수 있었다. 이들 재료에 대해 열피로 시험을 수행할 수 있는 장치를 사용하여 원통형 시편에 대해 열크랙의 발생과 길이를 측정하여 재료의 내열성을 평가하였다. 그리고 열피로 시험과정을 유한요소법으로 해석하고 Manson-Coffin 식과 주변형률을 이용하여 열피로수명을 평가하여 시험결과와 비교, 검토하였다. 해석에 의한 예측수명은 관찰영역의 균열의 총 길이가 40 ㎛ ~ 1㎜ 사이에 있을 때의 수명에 해당함을 알 수 있다. We measured the mechanical and thermal properties of four types of cast irons used for manufacturing the brake discs of railway vehicles. It was found that these properties could be controlled by varying the composition of Ni, Cr, and Mo. Thermal fatigue tests were carried out by using a thermal fatigue tester in which thermal cycles could be controlled. Thermal crack initiation and propagation were measured on cylindrical specimens. Finally, we simulated the thermal fatigue test procedure by finite element analysis and calculated the thermal fatigue lifetimes by Manson-Coffin’s equation and the maximum principal strain. The estimated thermal fatigue lifetimes corresponded to the measured lifetimes when the total crack length was 40㎛ ~ 1 ㎜.
구병춘(Goo Byeong-Choon),임충환(Lim Choong-Hwan) 한국철도학회 2007 한국철도학회 학술발표대회논문집 Vol.- No.-
Thermal cracks are among the key factors that control the quality of a brake disk. Thermal cracks may shorten the lifetime of the disc and increase brake noise. Therefore, high heat-resistant brake disk materials are needed. In this study, three kinds of disk material were tested. They are composed of C, Si, Mn, P, S, Cu, Cr, Mo, and Ni. For the three materials, tensile tests, hardness measurement, metallurgical structure analysis, image analyzer analysis, etc were carried out. And friction tests were performed by a small scale dynamometer.
CV 흑연 주철 제동디스크 개발 및 마찰ㆍ마모 특성 평가
구병춘(Goo Byeong-Choon),임충환(Lim Choong-Hwan),권성태(Kwon Sung-Tae),최준식(Choi Jun-Sik) 한국철도학회 2009 한국철도학회 학술발표대회논문집 Vol.2009 No.11월
Thermal cracks are among the key factors that determine the quality of a brake disk. Thermal cracks may shorten the lifetime of discs and increase brake noise. Therefore, high heat-resistant brake disk materials have been developed. In this study, three kinds of new disk material were developed and tested. Graphite forms are compact vermicular. For the three materials, tensile tests, hardness measurement, metallurgical structure analysis, measurement of thermal properties, etc were carried out. And friction tests were performed by a life-size brake dynamometer. It is found that the developed discs have good tribological characteristics.