Chul-Su Kim

Fatigue crack growth behavior of rail steel under mode I and mixed mode loadings

Abstract It is necessary to evaluate the fatigue behavior of rail steel under mixed mode loadings to assure the safety of railway vehicles. For this purpose, the stress analysis to investigate static failure and fatigue behavior under mixed mode loadings is performed. The stress analysis results show that the K I / K II tends to increase as the transverse crack below the surface propagates. For the mixed mode, the fatigue crack growth behavior was evaluated using various comparative stress intensity factor ranges Δ K V . Fatigue crack growth rate under the condition of mixed mode is slower than that under mode I, and this difference decreases with the increase of the stress ratio R .

Strength evaluation and failure analysis of unidirectional composites using Monte-Carlo simulation

Abstract Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber–matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulate the failure process of unidirectional composites. In this study, a Monte-Carlo simulation using 2-D and 3-D (square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

Technical Evaluation of Railway Transportation System with the Change of Gauge

Recently the increase in the exchange of goods between Europe and Asia caused by social and economic factors creates good opportunities for railways. At the same time, however, it becomes an enormous challenge for railway transport. There are different rail track gauges (i.e narrow/standard/broad gauge) on the continental transportation between Korea (TKR) and Eurasian (TCR/TSR). The existence of various track gauges is one of obstacles preventing the smooth flow of goods by rail. The transferring process system from one track gauge to another could vary with the types of cargo. Service operation of these systems has a decisive effect on working time and cost of storage and transshipment facilities at border crossings. In relation to the above-mentioned factors, it is important to examine the comparison between different methods of transferring goods in different track gauges. In this study, it was performed to evaluate the effectiveness of continental railway transportation systems through analysis scenarios and to suggest technical factors of them.

A Stochastic Analysis in Steam Turbine Blade Steel Using Monte Carlo Simulation

In this study, the failure probability of the degraded LP turbine blade steel was performed using the Monte Carlo simulation to apply variation of applied stress and strength. For this purpose, applied stress under the service condition of steady state was obtained by theoretical stress analysis and the maximum Von-Mises stress was 219MPa. The fatigue strength under rotating-bending load was evaluated by the staircase method. Furthermore, 3-parameter Weibull distribution was found to be most appropriate among assumed distributions when the probabilistic distributions of tensile and fatigue strength were determined by the proposed analysis. The failure probability with various loading conditions was derived from the strength-stress interference model and the characteristic factor of safety was also estimated.

A Study on an Impedance Matching Technique for Rail Power Line Communication

An auxiliary real-time train communications system among drivers, train-traffic controllers and field workers is necessary to share hazard information (i.e. rockfall detection, track maintenance) in low visibility zones (long tunnels and steep curved track). To develop the appropriate communication system, this paper proposes a new way of power line communication using the rail track (Rail PLC), which has little noise and distortion of attenuation. Therefore, it is important to measure the impedance of the rail and to apply an impedance matching technique to increase the transmission characteristic of the Rail PLC. This study would evaluate the reflection and the transmission characteristics of the rail using a network analyzer and an impedance matching transformer. The suitable impedance matching ratio was 1:3.28 from the result of back-to-back testing. The results confirmed that the transformer can improve the performance of the transmission signal in Rail PLC using an impedance matching technique.