Papers by Author: Young Shin Lee

Abstract: The combustor chamber, diffuser and nozzle are the main components of the ramjet engine. In this study, the thermal strength of the combustion chamber of the ramjet engine was evaluated. The combustion chamber consists of an Inconel alloy 718 liner and a 17-4Ph stainless steel housing. The liner is rapidly heated to a high temperature. The heated liner is cooled with a film cooling method that forms a cold boundary layer to separate the hot gas from the surface of the liner. The thermo-structural analysis is evaluated the thermal strength of super alloy structure with various thermal insulation performances by finite element method with code MSC/Nastran. The result of the analysis is compared with accelerated stress rupture test. The experiment is performed to get safety design and estimate actually life-time for combustor chamber under high temperature. In general, the work in this paper is helpful to further improve the understanding and evaluation of thermal strength of the super alloy structure with various thermal insulation performances.

Abstract: In this study, failure behavior of hot gas casing for gas turbine was investigated. The microstructure and damage mechanism of serviced hot gas casing were examined. Also low cycle fatigue tests of the Inconel 617 super alloy is used for structural material of hot gas casing were performed. To predict the low cycle fatigue life, Coffin-Manson and strain energy density methods were used.

Abstract: A fuel channel, which is the major structure of a nuclear reactor, is excited by the flow of cooling water during the operation of the nuclear reactor. This flow of cooling water can cause excessive vibration of the structure by the resonance. So, in the design process of a nuclear structure, the exact evaluation of the effect of water to modal characteristics and stiffness characteristics is very important to generate an exact analysis model. In this study, the effect of water height for modal characterisics of the fuel channel is investigated and the stiffness evaluation of that is conducted using the modal test results.

Abstract: The combat car used the heavy duty diesel engine must have a large output for maintaining excellent mobility. The compacted graphite iron (CGI) is a material currently under study for the heavy duty diesel engine demanded for high torque, durability, stiffness, fatigue. In this study, three dimensional finite element model of a heavy-duty diesel engine was developed to conduct the stress analysis by using property of CGI. The use of CGI property on the FE model was expected to result in improved distribution of distortions and stresses. The loading conditions of engine are assembly load and operational gas load.

Abstract: Autofrettage is used to introduce advantageous residual stresses into cylinders. The Bauschinger effect can produce less compressive residual hoop stresses near the bore than are predicted “ideal” autofrettage solutions. A723 steel is used for compound cylinder. This paper extends the analysis to material the addition of pressure or of shrink-fitting to the cylinders, providing associated residual stress profiles following various amounts of further yielding due to a net external pressure. The Bauschinger effects for “realistic” – Bauschinger effect dependent autofrettage are obtained. The 2-D analysis is performed via the finite element method. The Bauschinger effect is found to significantly lower the beneficial stress due to autofrettage.

Abstract: The hot mill spindle assembly is the important component of the hot rolling process and used for transmission of rotational power. The contact surface between end coupling and slipper metal have high stress concentration due to operation interference. The life cycles of slipper metal are reduced by the contact surface damage. In this study, the structural analysis and kinematics simulation are performed by applying the various driving angle and dynamic boundary condition of the mill spindle assembly. This study aims to minimize the contact damage which might happen in the production process.

Abstract: The most common mode of the gear failure is tooth breakage, which is usually produced by bending fatigue failure. It is important to manufacture the gears which can withstand the applied stresses in view of safety and economic requirements. In this study, fatigue test and analysis were performed to evaluate the bending fatigue strength of an automotive bevel gear. Test fixtures of the double tooth concept were considered to obtain reliable fatigue test results. Fatigue life of automotive bevel gear was evaluated by Weibull analysis. To compare the test results and to verify the fatigue analysis procedures, fatigue analyses were carried out. The results of fatigue analysis show that fatigue life and crack initiation sites were well agreed with test results. The random loading of bevel gear under the real driving conditions was defined here, and then the fatigue analysis under random loading was also performed.

Abstract: An experimental program has been carried out to address the thermo-mechanical fatigue life of the uncoated IN738LC nickel-base superalloy. High temperature isothermal Fatigue and out-of-phase(OP), in-phase(IP) TMF experiments in strain control were performed on superalloy materials. Temperature interval of 450-850
was applied to thermo-mechanical fatigue tests. The stress-strain response and the life cycle of the material were measured during the test. The plastic strain energy based life pediction models were applied to the stress-strain history effect on the thermo-mechanical fatigue lives.

Abstract: The objective of this study is to evaluate the mechanical properties of static, quasidynamic and dynamic fracture toughness of glass-filled ceramic as promising structural material for a dome port cover of a ramjet engine system. Static and quasi-dynamic tests were carried out using SEPB (Single Edge Pre-cracked Beam) specimens. Static and dynamic fracture toughness tests were also performed using ASTM and strain gage methods with SENB (Single Edge Notched Beam) specimens machined with various notch radii. The critical notch radius was evaluated. Below the critical notch radius, the static fracture toughness of the SENB specimen well agreed with that of the SEPB specimen.

Abstract: The purpose of the present study is to evaluate thermal shock properties of the ATJ graphite using laser irradiation techniques. Cracks of thermal shock specimens are initiated by maximum tensile stress field. Thermal shock resistance of the ATJ graphite is correlated with thermal parameter and mechanical property. To simulate the thermal stress conditions of rocket nozzle throat for the evaluation of the thermal shock resistance of ATJ graphite, the laser irradiation was applied at the central area of disk specimen. Thermal shock resistance was related to the geometry, the maximum stress, and the thermal and mechanical property. Also the analyses of transient temperature and thermal stress were performed by the finite element method with nonlinear code ABAQUS. Analyses were specially performed for several kinds of shape to determine the minimum power density which could be cracked the specimen. The shape of the thermal shock specimen which was cracked under the lower power density was obtained and the result will be proved to the test.