This study investigated the effectiveness of tap water application in reducing nano-sized wear particles at a wheel-rail contact interface and its impact on air quality at different train velocities. Airborne wear particles (AWPs) were simulated using a twin-disk rig at 500, 800, and 1,300 RPM. Mass concentration of nano-sized wear particles was measured using a fast mobility particle sizer (FMPS) at a sampling frequency of 1 Hz. To simulate various vehicle dynamics and contact conditions, the slip rate was incrementally increased from 0 to 3%. During wet conditions, water was applied at a rate of 7 L/min. PM0.1 and PM0.56 under dry and wet conditions were compared to evaluate the method’s effectiveness. The analysis showed that the tap water application method improved the air quality by reducing PM0.56 by at least 74% and PM0.1 by approximately 80%. In conclusion, the water application method can effectively improve air quality by reducing generation of nano-sized wear particles. The train velocity affected the generation of nano-sized wear particles under both conditions.
In mechanical braking systems, there are hot spots on the surface of a braking disc due to thermal deformation with a high thermal gradient. Controlling such hot spots is important for extending the life of a braking disc. In this study, surface temperatures of railway brake discs were monitored using infrared (IR) thermal imaging technique. A highspeed infrared camera with a maximum speed of 380 Hz was used to monitor surface temperature changes of the braking disc. Braking tests were performed with a full-scale dynamometer. During the braking test, the surface temperature change of the braking disc were monitored using a high-speed infrared camera. Hot spots and thermal damage observed on the surface of railway brake discs during braking tests were quantitatively analyzed using infrared thermographic images. Results revealed that monitoring disc surface temperature using IR thermographic technique can be a new method for predicting surface temperature changes without installing a thermocouple inside the disc.
The surface of railway wheels running on rails is subject to damage due to rail and frictional wear, damage from wheel tread and flange wear caused by curved track operations, and damage from flats and concave wear due to braking friction heat from brake shoes. Although the surface of wheels is regularly reprofiled through periodic grinding cycles, damage occurring to the wheel surface during operation can lead to deteriorated ride quality and potential failure due to crack propagation. In domestic railway components technical standards, wheel integrity is mandated to be demonstrated through non-destructive testing. To prevent and detect failures caused by damage occurring on railway wheels, it is necessary to develop methods that could detect and evaluate surface damage. The present study investigated a method for detecting and evaluating surface damage on railway wheels using electromagnetic imaging. Results demonstrated that defects with a length of 10 mm, a width of 0.8 to 1.0 mm, and a depth of 0.2 to 1.0 mm could be adequately detected using electromagnetic scan images.
The effectiveness of applying tap water method to reduce the generation of nano-sized wear particles from wheel-rail contacts in the aspect of air quality was investigated. A twin-disk rig was utilized to simulate the generation of airborne wear particles resulting from wheel-rail contacts. Slip rates ranging from 0 to 3% were continuously generated to simulate various railway vehicle dynamics. Dry and tap water application conditions (7 L/min) were tested. The mass concentration of wear particles with sizes below 560 nm generated during tests was measured using a Fast Mobility Particle Sizer (FMPS). Particles measured in the slip zone (0 to 3%) were categorized into PM0.02, PM0.03, PM0.1, and PM0.56 for analysis. Results indicated a significant decrease in mass concentration of particles with sizes above 30 nm, while those with sizes below 30 nm showed an increase. Particle reduction rate was -217.2% for PM0.02, -58.5% for PM0.03, 84.5% for PM0.1, and 90.3% for PM0.56. It should be noted that a negative reduction rate indicates an increase in the amount of particle generation. This study demonstrates that the application of tap water is effective in improving air quality by reducing the generation of nano-sized wear particles overall.
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Measurement and Analysis of Air Quality Improvement Effects of Applying Water Methods at Various Train Velocities Using a Twin-disk Rig HyunWook Lee Journal of the Korean Society for Precision Engineering.2024; 41(10): 753. CrossRef
The Technical Specification for Interoperability (TSI) legally mandates the prediction and verification process of the Reliability, Availability, Maintainability and Safety (RAMS) in signaling and communication systems. Recently, domestic regulations, including the Railroad Safety Act, have been strengthened in order to better meet the requirements for participating in international projects. To comply with these regulatory requirements, manufacturers and development organizations must prepare verification data pertaining to the reliability and safety of railway components and related systems. This paper aims to analyze the requirements of Failure Mode, Effects and Criticality Analysis (FMECA) through international laws and standards, and subsequently propose a compliant FMECA system for the domestic railway industry. The proposed FMECA system is then compared with the analysis results of actual failure data to determine its suitability for establishing a Reliability, Availability, Maintainability (RAM) verification standard for railway products in relation to conformity assessment.
Rails are important facilities related to safe running of trains. When buckling occurs due to thermal expansion, serious safety accidents such as train derailment can occur. Currently, operating organizations are building expensive temperature monitoring systems and automatic watering devices. However, they have limitations for universalization due to their costs. Recently, long-term rail temperature reduction effect has been demonstrated by applying thermal insulation paint to rail surface. However, when coating the rail surface with paint, it increases the difficulty of detecting defects through nondestructive testing, which is one of the important elements of rail maintenance. To solve this problem, previous studies have proposed a detachable thermal insulation fabric by coating the surface of a fabric with thermal insulation paint and attaching a magnetic material. In this study, effect of thermal insulation performance according to manufacturing method was analyzed to derive the optimal performance of the previously developed thermal insulation fabric. Experiment results confirmed that paint weight increased when the roller method was used compared to the spray method with temperature reduction performance improved. Finally, the most efficient and optimal paint weight ratio was derived when the roller method was applied.
Damage to the units related to driving and running of the railway vehicle may cause an inevitable accident due to defects and malfunctions in operation. In order to prevent such an accident, a non-destructive diagnostic technology that detects the damage is required. Previous researchers have researched and developed a monitoring system of the infrared thermography method to diagnose the condition of the railway vehicle driving and driving units. A system for monitoring running of the railway vehicle and temperature condition of the drive unit at a vehicle speed of 30 to 100 km/h was constructed, and a study on its applicability was conducted. In this study, a system for diagnosing an abnormal condition of the driving and running units while the vehicle is running with an infrared thermography diagnostic system was installed in the depot and operation route, and evaluation of the abnormal condition of the driving and running units was performed. The results show that the diagnosis system using infrared thermography can be used to identify abnormal conditions in the driving and running units of a railway vehicle. The diagnosis system can effectively inspect the normal and abnormal conditions in operation of a railway vehicle.
The brake squeal noise is a high-frequency noise over 1 kHz range generated by the contact between the brake pad and the disk. The purpose of this paper was to investigate the behavior of the squeal noise characteristics of the brake system from an instability point of view, according to the variation of major parameters such as friction coefficient between the flexible pad and the disk, brake pressure, and Young’s modulus of disk. Full nonlinear perturbed modal analysis using commercial finite element analysis program was performed to derive complex eigenvalue results of the model. And the sensitivity behavior was observed. Increasing the coefficient of friction or Young’s modulus of disk tended to make the squeal mode of the model more unstable. However, the change in brake pressure has a complicated nonlinear relationship with the squeal mode of the model. The judgment technique conducted in this study should be considered to be used in the design of the vibration point of the disk and pad of railway vehicles in the future.
The magnetorheological material changes its characteristics according to the external magnetic field. Magnetorheological elastomer existing in the solid phase has micrometer-sized magnetically responsive particles inside. When a magnetic field is applied by a permanent magnet or electromagnet nearby, it can exhibit stiffness that changes according to the strength of the magnetic field. Many previous studies focused on verifying the variability of the material"s characteristics. However, this study newly proposed a variable stiffness joint for the suspension system of railway vehicles using a magnetorheological elastomer, as a basic study of magnetorheological elastomer for a mechanical component. Based on the characteristics test of the magnetorheological elastomer, the variable joint was designed to have the same structure as the conventional guide arm joint of a railway vehicle. Particularly, to overcome the low magnetic field strength, which may be a problem in the previous research, and to implement uniform magnetic field distribution, the electromagnet was designed to make direct contact with the magnetorheological elastomer. A mathematical model was established and a finite element method verified the model, resulting in an average magnetic flux density of 300 mT, which means 30% stiffness change at 15% shear strain.
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The sanding device support bracket is part of the axle box and is one of the railway vehicles parts that must withstand extremely harsh environments. Conventional welded structure type brackets were cracked at welds during operation, requiring design changes. To minimize harsh environments and manufacturing errors, this review was conducted from the design stage, and design changes were made through several trial and error. In this paper, the optimal design was derived by performing topology optimization on the model designed and manufactured through trial and error and applied to the actual vehicle. The comparison of the existing model with the empirically designed model confirmed the improvement of the optimal design using the topology optimization. The optimized design was verified by the analysis and the vibration test of IEC 61373 was satisfied. The test parts based on the optimal design were applied to the actual vehicle and the performance was verified. In the optimum design process, the shape and material as well as the weight analysis were performed and finally the brackets were designed to be light in weight and improved in strength.
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Conventional railroad vehicles, that run on a line with high frequency of sharp curves, have problems such as wheel noise and wear, from insufficient passive steering. To solve this problem, real-time curvature measurement technology must be developed for realizing active steering. In this study, we propose a uniaxial curvature measurement sensor considering applicability to actual railroad vehicles, and analyze its validity in terms of active steering control. Required characteristics of the curvature sensor according to steering control performance, were determined through railroad vehicle dynamics simulations, and actual vehicle driving information. Measurement range of curvature radius is 200 m to 600 m; measurement accuracy is ±3%, and measurement bandwidth is 0.85 Hz. Effectiveness of the developed curvature sensor was analyzed based on behavior of the car body, the bogie and its installation on the vehicle, and curvature of the track was measured in real time on an actual urban railroad vehicle. As a result of the field test, curvature measurement error was obtained within 3%, validating the feasibility of active steering control for the next generation railroad vehicles.
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Linear roller bearings are often used for linear positioning systems due to high load-carrying capacity, precision, and durability. In this paper, guide rail deformation of linear roller bearings under vertical and horizontal loads, has been experimentally investigated. An experimental system was made to measure displacement of the carriage and guide rail deformation of a bearing with varying load. Guide rail deformation inaccessible inside the carriage, was estimated by measured carriage displacement subtracted from calculated carriage displacement from a commercial program, that does not consider flexibility of guide rail and base. In addition to estimated deformation, guide rail deformation outside the bearing carriage was measured to make a complete guide rail deformation curve due to external loads. Results revealed deformations occurring in guide rail and base are significant, as to affect bearing accuracy. Thus, deformations in guide rail and base should be considered, to estimate stiffness and motion accuracy of linear roller bearing under external loading conditions.
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This study reviews the assumption that the lightweight design of commercial vehicles is significant from the aspect of the anticipated fuel consumption and environmental regulations that are consequently applicable to those vehicles. Generally speaking, it is noted that among the numerous trailer components, a stub axle, which is designed to independently operate as an integral part of trailer’s suspension, can play an important role in increasing the shipping capacity of a box trailer. For this reason, because each stub axle is comparatively a heavy unit in itself, and a total of six stub axles are mounted in a box trailer, the lightweight design of a stub-axle is noted as an essential factor to reduce the whole weight of a trailer. For a finite element analysis, an original CAD model is modified through removing a chamber, airbag, axle drum, bearing and pivot on a vehicle. In addition, the loading conditions are imposed considering three extreme driving conditions and the effects are studied when in the event of review of a fully loaded in a box trailer. A topology optimization is conducted to determine a lightweight design for minimizing compliance under these boundary conditions.
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Carrying out accurate and reliable track maintenance tasks is very important to improve the running safety of a railway vehicle and the ride quality for the passenger. For this purpose, appropriate track management standards need to be set by analyzing the field test results for setting reliable management criteria. However, in practice, it is difficult to quantitatively examine the various track fault conditions. Therefore, investigation of the influence of various track characteristics on the running safety and ride quality was performed through numerical analysis method. The influence of the track irregularities on the wheel lateral forces, derailment coefficients, and accelerations on the bogie and car body was investigated through numerical analysis.
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Rolling contact fatigue (RCF) and wear caused by rolling contact between the wheel and rail are inevitable problems in railway systems. An increase in axle load or the slip ratio causes excessive wear. However, RCF and wear do not act independently, but one influences the other. Wheel and rail materials and manufacturing quality have a considerable influence on the formation of RCF and the ensuing wear. Therefore, the mechanical properties of the wheel and rail are important factors for reducing RCF and wear on the contact surface. This paper presents a comparative evaluation of the wheel and rail used in the Korean industry for high speed trains and conventional rails with respect to their fatigue and fracture behavior. A series of tests such as uniaxial tensile tests, fracture toughness tests, and fatigue crack growth tests were carried out at both room temperature and low temperatures.
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