• 한국산학기술학회논문지
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• 제11권4호
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• pp.1178-1185
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• 2010

철도차량의 고속화가 가속화되면서 화물을 운송하던 컨테이너 차량이 차륜의 파손에 의하여 탈선하는 사고가 발생하여 많은 물적 피해가 발생하고 있으며, 이러한 철도차량의 사고는 많은 인명 피해와 물적 피해를 가져오는 대형 사고로 발전할 수 있다. 따라서 이에 대한 재발 방지를 위한 차륜의 파손 해석에 대한 연구가 필요한 실정이다. 철도차량의 차륜은 기계적 하중과 열하중를 동시에 받으며, 기계적 하중으로는 철도차량의 무게에 의한 수직하중과 곡선 구간을 운행할 때 차륜과 레일의 접촉부에 수평하중이 발생하며, 철도차량의 제동시 답면제동에 의한 반복적인 열하중을 받는다. 이러한 차륜에 발생하는 기계적 하중과 열하중은 차륜의 균열과 잔류응력 등을 발생시키는 것으로 알려져 있다. 따라서, 본 연구에서는 차량 주행 시의 브레이크 이력과 하중 조건을 고려한 열 구조 연성해석을 수행하여 차륜에 부하되는 최대응력을 추정하였으며, 이 값을 파괴역학 파라미터인 응력확대계수에 적용하여 차륜의 안전성을 평가하였다.

• 한국자동차공학회논문집
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• 제22권5호
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• pp.44-49
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• 2014

As expansion and contraction of bike disk brake are happened continuously by temperature at repeated urgent braking. In this study, 3 kinds of model are designed according to configurations of holes and thermal durabilities on bike disk brake are investigated by comparing 3 models through temperature and thermal analyses. Maximum thermal stress happened at the disk contacted with pad and the connection part fixing disk rotor. Instead of initial state, the temperature is uniformly distributed at transient state. As the area of hole at disk rotor face becomes wider, thermal stress becomes lower at the initial state. On the other hand, in case the number of holes increases, thermal stress becomes lower at the elapsed time of 100 seconds. The thermal durability of bike disk brake can be improved by applying this study result with configurations of holes.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.160-167
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• 2002

The transient thermoelastic analysis of automotive disk brakes with frictional contact is performed by using the finite element method. To analyze the thermoelastic behaviors occurring in disk brakes, the coupled heat conduction and elastic equations are solved. The fully implicit transient scheme is used to improve the computation accuracy at every time step. The numerical results of the thermoelastic behaviors are obtained during the repeated braking condition. The computational results show that the thermoelastic instability(TEI) phenomenon(the growth of non-uniformities in contact pressure) occurs in disk brakes. Also, the effect of material properties on the thermoelastic behaviors is investigated to facilitate the conceptual design of the brake system.

• 자동차안전학회지
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• 제7권3호
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• pp.19-24
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• 2015

Brake pads are a component of disc brake system of automobile and consist of steel backing plates and friction material facing the disk brake rotor. Due to the repeated sliding forces and torque in vehicle braking, friction performance of brake pads are ensured. Futhermore, the brake pad is one of major tuning components in aftermarket, mechanical characteristics of the brake pad are necessary to evaluate for establishing the certification standards of tuning components. This study had performed the five specimen tests for friction coefficients and wear loss rates according to the SAE test specification. Using the instrumented indentation method, yield strength and tensile strength were measured. Friction coefficients, 0.386 - 0.489, and wear loss rates, 1.0% - 3.7% are obtained. The range of yield strength and tensile strength are 21.4 MPa - 105.3 MPa and 39.5 MPa - 176.4 MPa respectively.

• Environmental Engineering Research
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• 제24권4호
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• pp.680-689
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• 2019

Temperature effects on the generation of brake wear particles from railway vehicles were generated, with a particular focus on the generation of ultrafine particles. A real scale brake dynamometer test was repeated five times under low and high initial temperatures of brake discs, respectively, to obtain generalized results. Size distributions and temporal patterns of wear particles were analyzed through visualization using clustered heatmaps. Our results indicate that high initial temperature conditions promote the generation of ultrafine particles. While particle concentration peaked within the range of fine sized particles under both low and high initial temperature, an additional peak occurred within the range of ultrafine sized particles only under high initial temperature. The timing of peak occurrence also differed between low and high initial temperature conditions. Under low initial temperature fine sized particles were generated intensively at the latter end of braking, whereas under high initial temperature both fine and ultrafine particles were generated more dispersedly along the braking period. The clustered correlation heatmap divided particle sizes into two groups, within which generation timing and concentration of particles were similar. The cut-off point between the two groups was approximately 100 nm, confirming that the governing mechanisms for the generation of fine particles and ultrafine particles are different.

• 한국운동역학회지
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• 제26권1호
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• pp.31-37
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• 2016

Purpose: The purpose of this study was to investigate the differences in FT (free-torque) components between non-fatigue and fatigue conditions induced by prolonged running. Methods: Fifteen healthy runners with no previous lower-extremity fractures ($22.0{\pm}2.1$ years of age) participated in this study. Ground reaction force data were collected for the right-stance phase for 10 strides of 5 and 125-min running periods at 1,000 Hz using an instrumented force platform (instrumented dual-belt treadmills, Bertec, USA) while the subjects ran on it. The running speed was set according to the preferences of the subjects, which were determined before the experiment. FT variables were calculated from the components of the moment and force output from the force platform. A repeated-measures one-way ANOVA was used to test for significant differences between the two conditions. The alpha level for all the statistical tests was 0.05. Results: The absolute FT at the peak braking force was significantly greater after 5 mins of running than after 125 mins of running-which was regarded as a fatigued state-but there were no significant differences in the absolute peak FT or impulse between the conditions. Conclusion: The FT variables in the fatigue condition during prolonged running hardly affect the tibial stress syndrome.

• Elastomers and Composites
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• 제54권4호
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• pp.299-307
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• 2019

Rubber friction properties include adhesion friction characteristics of the interface, hysteresis friction characteristics originating from repeated rubber deformations, and cohesion friction characteristics due to wear and tear. Cohesion friction is generally sufficiently small (< 3%) that it can be ignored, whereas adhesion friction has a relatively large contribution of 15%, but has not been investigated thoroughly. Therefore, through an adhesion friction study, the adhesion mechanism was examined and the relationship between friction characteristics and adhesion friction on dry surfaces was derived. The wet grip characteristics of tread rubber are fully described by the hysteresis characteristics of tires, but friction characteristics on dry roads are difficult to determine without adhesion factors. The results presented herein demonstrate that the combination of hysteresis and adhesion properties in the tread rubber sufficiently explained the characteristics of the dry grip. Based on the results of this study, technologies will be developed to determine the key factors governing adhesion friction characteristics and improve dry tire braking performance.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2011년도 제43차 동계학술발표논문집 19권1호
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• pp.107-108
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• 2011

철도기술의 발전 이후 현재 도시철도에서는 국내 처음으로 열차의 안전한 운행 제어를 위한 자동/무인 운전이 가능한 자동 열차 운행 장치(ATO)를 도입해 안정적으로 정시 운행을 하고 있다. ATO 자동운전은 제어기준 값(목표속도)과 피드백 값(실제속도)간의 오차에 의한 전동차의 역행과 제동을 반복함으로 에너지 효율 낮다. 본 논문에서는 고정된 역간 거리를 정해진 운전 시분 내에 주행에너지를 최소화하며 주행하는 열차의 특성을 파악하고 모델링한다. 따라서 5호선 실 노선 구간별 운전시분 내에서 실측 데이터 분석을 위해 직선구간/구배구간/곡선구간 등 구간을 선정하고 그 구간에서 열차의 주행패턴에 따라 변화하는 주행에너지를 최소화하는 최적의 주행 패턴을 제시하였다.

• 한국정밀공학회지
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• 제20권12호
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• pp.55-63
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• 2003

The traffic accident is the prerequisite of the traffic accident reconstruction. In this study, the traffic accident (forward collision) and traffic accident reconstruction (inverse collision) simulations are conducted to improve the quality and accuracy of the traffic accident reconstruction. The vehicle and tire models are used to simulate the trajectories for the post-impact motion of the vehicles after collision. The impact dynamic model applicable to the forward and inverse collision simulations is also provided. The accuracy of impact analysis for the vehicular collision depends on the accuracy of the coefficients of restitution and friction. The neural network is used to estimate these coefficients. The forward and inverse collision simulations for the multi-collisions are conducted. The new method fur the accident reconstruction is proposed to calculate the pre-impact velocities of the vehicles without using the trial and error process which requires the repeated calculations of the initial velocities until the forward collision simulation satisfies with the accident evidences. This method estimates the pre-impact velocities of the vehicles by analyzing the trajectories of the vehicles. The vehicle slides on a road surface not only under the skidding during an emergency braking but also under the steering. A vehicle over steering or cornering with excessive speed loses the traction and leaves tile yaw marks on the road surface. The new critical speed formula based on the vehicle dynamics is proposed to analyze the yaw marks and shows smaller errors than ones of the existing critical speed formula.

• 드라이브 ㆍ 컨트롤
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• 제15권3호
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• pp.14-20
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• 2018

Wet clutches in an automatic transmission enable the transmission of the engine power by the frictional torque experienced and noted between disk and plates. Since the clutch frictional torque considerably affects the shift quality of an automatic transmission as well as the durability of the machinery, its friction characteristics must be carefully examined to meet the design requirements. The SAE No. 2 friction test machine is a well-known standard to evaluate mainly the friction characteristics of plate clutches along with the required automatic transmission fluids. This paper reviews the experimental analysis of the wet clutch friction characteristics by using the exclusively developed clutch test machine which is capable of controlling the clutch test procedure, in accordance with the applicable test standard and processing of the experimental data automatically. As the clutch test machine is designed for the accommodation of dual clutches which is applied to the real transmission, it can evaluate not only the clutch friction characteristics, but also an actuation performance of a measured clutch piston. In respect to friction characteristics involving dynamic friction coefficients, the energy absorbed in a clutch disk and the recorded temperatures of clutch plates during braking actions and procedures are also investigated. Additionally, the change of friction coefficients by the use of the repeated clutch application is also observed with the endurance test functions of an accurately calibrated and dedicated clutch test machine.