Key Engineering Materials Vols. 321-323

Abstract: Generally, the shape of graphite and the contents of elements strongly affect the tensile strength of cast iron. In this study, hardness tests and tensile tests for the two types of gray cast iron were carried out. The test results showed the similarity in the hardness but considerable difference in the tensile strength between two materials. Microstructure analysis and chemical analysis were conducted to determine the cause for the difference in the tensile strength between the two types of cast iron. The experimental results showed differences in the microstructure and chemical composition between the two materials. B-type brake disk material(B-type) that had higher tensile strength includes flake, vermicular and spheroidal graphite, whereas A-type brake disk material (A-type) included only flake graphite in the structure. Nodularity of graphite in the B-type was higher than that in the A-type. Also, the B-type had the higher Si content and lower Mn content. In addition, the B-type had Cu, while the A-type did not. Therefore, we concluded that the difference in the strength between the two types of cast iron was due to the difference in the shape of the graphite and the contents of Cu in the cast irons.

Abstract: In the present paper, the induced current focusing potential drop (ICFPD) technique is applied to the detection of surface and internal defects for railway wheels. To detect the defects for railway wheels, the sensors for ICFPD are optimized and the tests are carried out with respect to 4 surface defects and 3 internal defects each other. The results show that the surface defect of 0.5 mm and internal crack of 1.0 mm apart from surface of wheel tread could be detected by using this method. The ICFPD method is useful to detect the defect that initiated in the tread of railway wheels.

Abstract: This study was aimed at evaluating the durability of the car body for rubber-tired light rail vehicles according to Korean-standardized specifications for light rail vehicles (size, strength, structure, weight, etc.). The strengths of the car body were analyzed under two weight conditions (tare weight and maximum passenger weight) by using the finite element method. Based on the results of the analysis, dynamic stresses were measured by using strain gauges, including rosette gauges, while the train was running on the test track. Various experimental results have verified the durability and safety of the car body.

Abstract: This study was aimed at evaluating the structural safety of the new bogie frames for Korean-standardized rubber-tired AGT vehicles. The guidance frame and the rotation frame were designed according to Korean-standardized specifications for rubber-tired AGT vehicles, and their stresses were analyzed by using the finite element method. Based on the results of the analysis, dynamic stresses were measured while the train was running under various conditions in the test track. Analytical and experimental results verified the structural safety of the new bogie frames.

Abstract: In this paper the fretting wear of press-fitted specimens under partial slip conditions was simulated using finite element method and numerical analysis based on Archard's equation. An elasto-plastic analysis of contact stresses in a press-fitted shaft in contact with a boss was conducted with finite element method and the amount of microslip and contact pressure due to bending load was estimated. The predicted wear profile of press-fitted specimens at the contact edge was compared with the experimental results. It is found that the depth of fretting wear by repeated slip between shaft and boss reaches the maximum value at the contact edge. The initial surface profile is continuously changed by the wear at the contact edge, and then the corresponding contact stresses and strain are redistributed.

Abstract: The important factor to evaluate the running safety of a railway vehicle would be the interaction force between wheel and rail(derailment coefficient), for which is one of important factors to check the running safety of a railway vehicle that may cause a tragic accident. Especially, a newly developed vehicle that first runs commercially requires necessarily the measurement and evaluation of derailment coefficient for securing the safety of a vehicle while measuring the derailment coefficient in view of securing running safety could be the more important factor than any other factors. In the meanwhile, it should be also measured the interaction force between wheel and rail in view of track maintenance as well as running safety because increased weight of a vehicle while it is running over a railway may cause damages or destruction on track components such as rails, sleepers and etc consisted of track and any rapid distortion of track. For the reason, the study was intended to evaluate the curving performance and the running safety from the analyses of dynamic running properties, manufacturing wheel axes to measure the working operation of wheels/rail, static load test, derailment coefficient calculated by running test on main track, ratio of wheel unloading, lateral force tolerance of the vehicle that is newly manufactured and commercially running on Gwangju Urban Railway and describe the results.

Abstract: High strength materials have been used for critical components in order to ensure the reliability of aircraft gas turbine engine. But it usually costs high to maintain their premium quality. Therefore, the optimum quality level of materials should be defined under operating condition by material property estimation technique in order to meet the requirement of reliability and economical efficiency. Most cast rotating parts of gas turbine engine have casting defects caused during the casting process. The casting defects less than certain acceptable limit can be permissible for usage. So, it is very important to understand material defect shape and distribution, and its effect on mechanical properties exactly. In this study, 17-4PH stainless steel specimens with variable internal casting defects were prepared to investigate the fatigue property characteristics. The defect fraction and condition were estimated in microstructure by statistical analysis. The correlation between estimated defect condition and fatigue property was discussed.

Abstract: This paper presents a method for diagnosis of railway arrester considering uncertainty. Arresters, a protective device that prevents damage due to transient voltages, deteriorate due to the absorption of moisture, repetitive operation during over-voltages and manufacturing defects. Various diagnostic techniques are available for monitoring deterioration of arresters. The technique based on the amplitude of leakage current measures the root mean square or peak values of leakage current components. After measuring the total leakage current, harmonics of leakage current components are analyzed by using a microprocessor based device. The level of leakage current is indicative of the arrester conditions. Harmonics of leakage current components occur due to nonlinear characteristics of railway arrester. Since leakage current contains uncertainty characteristics of power source, the probability density functions of leakage current components can be obtained for ZnO arrester. This paper presents a probabilistic approximation method for the harmonic currents analysis in diagnosis for railway arresters. Mean and variance of harmonic currents in railway system are obtained based on leakage current components. These statistical measures can be helpful to reduce the diagnostic error for railway arrester.

Abstract: The detection of interfacial micro-delamination in the thin-layered structure such as the electronic package becomes very important as the electronic device becomes smaller and thinner. The conventional method used to detect the delamination in an electronic package is to use a scanning acoustic microscope (SAM). However, despite its high performance qualities, SAM is often faced with a tricky decision when a delaminated gap is too small. In this paper, a novel method based on ultrasonic nonlinearity is proposed to overcome this limit. The proposed method is integrated into the conventional SAM equipment, and its effectiveness is verified by experiments for the Newton Ring and the real semiconductor package that have micro-delaminations. The results showed that the nonlinear parameter had good correlation with the gap size of delamination. A method of imaging the nonlinear parameter is also proposed to assure the feasibility of the proposed method in the field application.

Abstract: In this research, we used nondestructive test based on ultrasonic test as inspection method, and made up inspection robot in order to control of ultrasonic probe on the SWP surface, and programmed to signal processing code and pattern classifying code by user made programming code. For evaluation of flaw signal is reflected on welding flaw, user-made program codes are composed of signal processing and probability neural network (PNN) and backpropagation neural network (BPNN). And then, we actually confirmed to the theoretical advantage of each neural network method compared probability neural network with backpropagation neural network for classification and recognition rate. For the application of classifier to SWP inspection system, BPNN classifier is adequate in the first stage. And then, the application of PNN classifier is adequate as the next stage. Because of PNN application need enough sample data that is due to probabilistic density function.