Key Engineering Materials Vols. 321-323

Abstract: This study was aimed at identifying failure mechanism and strength of brazed copper pipe used in household air conditioner. For these ends, the brazed joints with various brazing length were manufactured according to manufacturer’s recommended methods. The 3-dimensional X-ray technique was used to identify internal flaws and their failure mechanism in brazed joints. And, strength of brazed joint was evaluated by static tests. To evaluate the effect of heat on the brazed joints, the micro-Vickers hardness is measured. Also, bursting tests were performed for burst pressure of brazed joints by using of self-designed internal pressure bursting tester.

Abstract: An efficient and accurate hybrid reliability method is developed to quantify the risk of an axially loaded pile considering pile-soil interaction behavior and uncertainties in various design variables. It intelligently integrates the concepts of the response surface method, the finite difference method, the first-order reliability method, and the iterative linear interpolation scheme. Uncertainties associated with load conditions, material and section properties of the pile and soil properties are explicitly considered. The algorithm is verified using the Monte Carlo Simulation technique.

Abstract: In designing the structures of railway rolling stocks, deterministic methods associated with the concept of a safety factor have been traditionally used. The deterministic approaches based on the mean values of applied loads and material properties have been used as safety verification for the design of the car body structures. The uncertainties in the applied loading for the high speed train and the strength of new materials in the structure require the application of probabilistic approaches to ensure fatigue safety in the desired system. Pressure loadings acting on the car body when the train passes through tunnels show reflected pressure waves for high-speed trains and they may cause a fatigue failure in vehicle bodies. In this paper, it is proposed that a fatigue design and assessment method based on a structural reliability that deals with the loading of pressure variations on a railway vehicle reflected in tunnels and the strength variations of material. Equation for the fatigue reliability index has been formulated to calculate the reliability assessment of a vehicle body under fluctuating pressure loadings in a tunnel. Considered in this formulation are the pressure distribution characteristics, the fatigue strength distribution characteristics, and the concept of stress-transfer functions due to the pressure loading.

Abstract: The importance of evaluation and establishment during product development process, for the reliability and safety of mechanical system and parts, is getting increased in the field of mechanical and electronic industry. The object of this paper is to suggest the reliability assessment method for machine tools using failure mode analysis and to introduce two web-based analysis programs which save all data related to failure rate, failure mode, and failure component. In order to evaluate the reliability of machine tools, this paper takes three steps: the use of previous database, the failure rate estimation using failure history data, and the failure mode analysis using performance test.

Abstract: Reliability of automotive parts has been one of the most interesting fields in the automotive industry. Especially small DC motor was issued because of the increasing adoption for passengers’ safety and convenience. For several years, small DC motors have been studied and some problems of a life test method were found out. The field condition was not considered enough in the old life test method. It also needed a lot of test time. For precise life estimation and accelerated life test, new life test procedure was developed based on measured field condition. First, vibration condition on vehicle and latent force on fan motor shaft were measured and correlated with each other. Second, test condition was decided by obtained data. Finally, life of fan motors was estimated by new life test method in shorter test time.

Abstract: The reliability estimation of pipelines is performed with help of the probabilistic method which considers the uncertainties included in the load and resistance parameters. The FORM (first order reliability method) is carried out to calculate the failure probability of corroded pipeline for the classified six distribution types of random variables. And the reliability of pipelines is assessed by using the failure probability. Furthermore, the MCS (Monte Carlo Simulation) is used to verify the results of the FORM. It is noted that the failure probabilities of the linear and the power models for surface corrosion are similar and those of the two-phase model for surface corrosion are somewhat different for six cases of two failure pressure models such as ASME B31G and MB31G models. And it is also found that the FORM and the MCS give similar results for varying exposure time.

Abstract: The carbon dioxide (CO2) is investigated as an alternative refrigerant to replace HFC (hydro fluorocarbon) refrigerants in refrigerators and air conditioning systems due to the environmental concerns. Because new compressors with the carbon dioxide are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressors, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN, and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. The vane-on-disk type sliding tests were carried out under the various sliding speeds, normal loads, and carbon dioxide pressures with an exclusive high pressure wear tester. From the tests wear volume of vane surfaces applied various coatings were compared. During the tests coefficients of friction and surface temperatures were monitored. Test results showed that WC/C coatings showed good tribological properties. TiN and CrN coated vanes showed good wear resistance properties but produced high friction.

Abstract: The tribological performances of two types of oilless sintered-metal bearings with varying loads were investigated. One is the Cu-based bearing and the other is Fe-based bearing. The frictional forces of the bearings were measured using the bearing tester. By measuring the change of weight before and after sliding tests, the oil losses of the bearings were surveyed. Also, PV curves, which could be used to predict the life of the oilless bearing, were plotted. By observing the roundness, the cylindericity and the images of scanning electron microscopy of bearings before and after sliding tests, the tribological characteristics of the bearings were evaluated. It was found that Fe-based bearing show lower friction, more oil loss, less wear and longer life than Cu-based bearing.

Abstract: This paper presents a study of KDA(kernel discriminant analysis) in gearbox failure feature extraction and classification. Experimental gearbox vibration signals measured from normal, gear small spall, gear severe spall and gear wear operating conditions are analyzed using either KPCA(kernel principal component analysis) or KDA as the feature extraction and fault classification methods. Experiment results indicate the effectiveness and the
superiority of KDA for gear fault classification over KPCA.

Abstract: The Korea Research Institute of Standards and Sciences has developed and maintained leak standards systems, and has accumulated much data on leak standards that have been disseminated during calibration and testing services. We have found that the indicative value of a leak detector and a halogen leak detector varies a lot, depending on the conditions encountered during sniffer mode operation. Therefore, to measure the reliability of the leak rate or when performing a leak test, proper test conditions are necessary. In addition, we found that the reliability increased when we used a guide tube that could influence the flow of air.