Papers by Author: Chul Su Kim

Abstract: To reduce the cost and the time of transport in Eurasian railroad networks such as TKR(Trans-Korea Railway), TCR(Trans-China Railway) and TSR(Trans-Siberia Railway) owing to the problem of different track gauges (narrow/standard/broad gauge), it is important to develop the gauge-adjustable wheelset (GAW) system to adapt easily to these gauges. The GAW system in the transcontinental railway represents a more effective way in comparison with other techniques for overcoming difference in track gauges. Freight trains having the GAW system will be passing various curved tracks in railroad networks. In this study, it was performed to evaluate contact stress and fatigue life of locking parts during freight trains' service in the curved track, respectively. Moreover, the safety of Korean GAW system at running track was verified by rig tests according to UIC 510-4 code.

Abstract: To reduce the cost and time of transport due to the different track gauges(narrow, standard, broad) in the Eurasian railroad network such as TKR(Trans-Korea Railway), TCR(Trans-China Railway) and TSR(Trans-Siberia Railway), it is very necessary to develop and adapt the gauge-adjustable wheelsets system. The freight trains’ with gauge-adjustable system could operate on the different track gauges in the transcontinental railway. Therefore, to assure the safety of the newly developed gauge-adjustment wheelsets system, it is essential to evaluate integrity of locking parts in the system by using fatigue analysis. In this study, it was performed that contact stress analysis of locking parts by using FEM(Finite Element Method) in the case both the gauge changeover operation and freight trains' service in the curved track, respectively. Besides, to consider the variation of fatigue data, the crack initiation life was statistically evaluated.

Abstract: The fatigue life in arc welded parts of the chassis component of SAPH45 steel in automobile is affected by various defects and residual stress due to welding. Moreover, it is hard to measure directly the crack initiation length of the welded part in chassis component due to the complicated geometric shape. Therefore, to assure the safety of vehicles, it is necessary to evaluate the crack initiation life by using a non-destructive technique (NDT). In this study, the acoustic emission measurement was adapted to monitor the crack initiation of the welded part during the fatigue test. The crack initiation length was verified by a computerized image processing system under stroboscopic light illumination. Besides, to consider the variation of fatigue data, the crack initiation life was statistically evaluated.

Abstract: The transverse crack, which is the most dangerous damage among the various types of rail defects, is developed from shelling near the rail running face, and grows perpendicular to the rail surface. Therefore, to assure the safety of rolling stocks, it is necessary to investigate the fatigue crack growth behavior of a gas pressure welded part of rail steel under mode I and mixed mode loadings. In this study, the fatigue crack growth behavior under the mixed mode was discussed by using comparative stress intensity factor ranges proposed by Richard. In addition, to evaluate the effect of the crack closure quantitatively, the crack opening load was determined a using clip-on gauge and computerized image processing system. As a result of this, a mixed mode crack growth rate regardless of the stress ratio could be correlated with the effective comparative stress intensity factor ranges derived from the crack opening loading.

Abstract: The temperature dependence of the tensile properties and the fracture toughness of the cold-worked STS 304 stainless steel have been examined in the temperature range of 293 K to 111 K. The tensile strength significantly increases with a decrease in temperature, but the 0.2% yield strength is relatively insensitive to temperature. The total elongation at 193 K abruptly decreases by 50% of that at 293 K, and it decreases slightly at 193 K to 111 K. The strain hardening exponents at low temperatures are about four times as high as that at 293K. Initiation fracture toughness (Jc) and tearing modulus (Tmat) tend to decrease with a decrease in temperature. The Jc values exhibit an inverse dependency on the effective yield strength (σflow) at all the test temperatures. Fractographic examination revealed that the critical stretch zone width (SZWc) at room temperature was about three times as large as that at 111 K. This indicates that the variation in fracture toughness according to temperature corresponds to the decrease in SZWc with decreasing temperature.

Abstract: In order to evaluate the variation of fatigue data of turbine blade steel in low pressure (LP) steam, it is important to estimate probabilistic stress-life (P-S-N) curve to accurately define the probability distribution. In this study, a new procedure was introduced to determine the expression of P-S-N curves. For this purpose, 3-parameter Weibull distribution was found to be the most appropriate among assumed distributions when the probability distributions of the fatigue life were examined by a comparative analysis. Furthermore, the parameter of P-S-N curve was evaluated using various optimization techniques to maximize the correlation coefficient. As a result, the sequential linear program method is used for estimation of P-S-N curve.

Abstract: The optimum welding condition for the input power was experimentally determined using the ERW simulator. The optimum condition derived from the nondestructive defect inspection and impact energy was the heat input power of 250kW with normalizing treatment at 900oC. In order to evaluate the fatigue life of ERW pipes, fatigue crack growth test for base metal and weld joint with the optimum condition were performed. As stress intensity factor range ( DKS) increased, the fatigue crack propagation rate (da/dN) of the weld joint became slower than that of the base metal. The fatigue life of ERW pipe was statistically estimated using Monte-Carlo simulation with the standard deviation of material constants (C and m) of the Paris law in the specimen. The fatigue life at failure probability PF = 50% is 2.3×105 cycle. Since the fatigue test of pipe in field has a lot of difficulties due to cost, equipment and time, the life derived from the simulation was identified using the common durability simulation software.