Papers by Author: Won Jo Park

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Authors: Hua Wei Rong, Hyung Jim Kim, Won Jo Park
Abstract: At present, welding technology is not only emphasized in the development of manufacturing technology but also application is expanding. In these systems, application of SUS as high-temperature material which is used for special purposes is attempted, and improvement of manufacturing technologies bear watching together with increase of using rate. Specifically, Wings with surface of three-dimensional shape usually applied to Fastener with purpose of lightweight. However, due to development of welding technology, methods of existing assembly tend to be replaced by welding, recently. Specifically, if laser welding techniques is applied, it minimizes heat-affected zone than other welding techniques. However, in the case of these special welding, residual stress is raised, and it fatally affects fatigue life. In order to remove residual stress and delay effect of fatigue life, shot-peening is executed; it executes shot-peening and verifies delayed effects of fatigue life. The intention of this study is to obtain the optimal conditions of shot-peening
Authors: Md. Anowar Hossian, Man Bae Lim, Sun Chul Huh, Won Jo Park
Abstract: This study evaluated fatigue crack growth characteristics, Besides consider compressive residual stress effect and verified the most suitable shot peening velocity. Fatigue crack growth delay effect was compressive residual stress, but over peening did action projecting velocity that accelerate fatigue crack growth rate. X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface. Fracture mechanics parameters could be estimated by the measurement of X-ray parameters, and the fractography observation was performed using a scanning electron microscope (SEM) for fatigue fracture surface. As the shot peening velocity increases, striation width increased. The changes in X-ray material parameters described above are directly related to the process of fatigue until the initiation of fatigue crack and X-ray diffraction pattern is thought that failure prediction with stress distribution is possible.
Authors: Won Jo Park, Chu Yong Kim, Sun Chul Huh, Kwang Young Lee
Abstract: An aluminum borate whisker (Al18B4O33w) was recognized as an attractive reinforcement for the aluminum alloy, It is good strength, high wear resistance, good thermal stability and low cost, comparable with those of other whiskers such as SiC and Al2O3. In general, aluminum borate whisker reinforced AC4CH alloy composites have been produced by squeeze casting process, which is capable of promoting the higher specific mechanical properties. α+Al18B4O33w/AC4CH (α: SiO2, Al2O3, TiO2sol) composites were fabricated by squeezecasting method in which the molten aluminum infiltrated into the whisker preform. The primary objective of this study was to establish the influence of the fracture toughness of α+Al18B4O33w reinforced composite by different containing inorganic binder. In addition, the fracture mechanism was evaluated through the scanning electron micrographs. As results, fracture toughness the composite containing TiO2 sol was shows plane about 9.28Mpa-m0.5. TiO2 inorganic binder can enhance fracture toughness of the Al18B4O33w reinforced composite. In order to obtain Al18B4O33w reinforced aluminum composites to have good fracture toughness use of TiO2 inorganic binder is recommend.
Authors: Sun Chul Huh, Yong Gil Jung, Won Jo Park, Jae Joon Sim
Abstract: Small Butterfly valve is specially designed for use in industry field and ship. The important parts of butterfly valve are composed of disk, stem and body. But, like LNG ship, in enviroment of low temperature, as working condition deteriorates, important of sealing more increased. In this study, we examine sealing mechanism of butter valve on the base of FEM and investigate sealing life by measurement. The finite element analysis was carried out to study the effect of the seal ring shape on bi-directional sealing force of valve. The sealing mechanism was evaluated by 2-dimensional model in order to save the analysis time. And these analyses used by material non-linearity and contact element were implemented.
Authors: Won Jo Park, Sun Chul Huh, Sung Ho Park
Abstract: Small steel ball is utilized in Shot peening process. Called “shot ball” are shot in high speed on the surface of metal. When the shot ball hit the surface, it makes plastic deformation and bounce off, that increase the fatigue life by compressive residual stress on surface. In this study, the results of observation on the tensile strength, hardness, surface roughness, compressive residual stress and fatigue life of a shot peened Al6061-T651 were obtained. Experimental results show that arc height increase tremendously by shot velocity. Also, it shows that surface roughness, hardness, compressive residual stress and fatigue life increase as shot velocity increase.
Authors: Tae Hoon Song, Kwang Young Lee, Sun Chul Huh, Won Jo Park
Abstract: The Cam nose part of the Automobile's Cam shaft is strongly bumped with rocker arm or valve-lift. Therefore abnormal wear such as unfair-wear and early-wear occur in the surface. This abnormal wear causes a defect that bad timing open and close actions of the engine valve happen in the combustion chamber so the fuel gas will be combustion imperfect. Therefore, the Cam shaft has to be high hardness and wear resistance. In this study, high frequency heat treatment method was accomplished for wear test for material SM53C.
Authors: Kelimu Tulugan, Ho Jun Hwang, Hua Wei Rong, Won Jo Park
Abstract: At present many researches are about low density and high strength material, Metal Matrix Composite (MMC) is one kind of high performance material which is very popular and can fit that condition very well. In this study, matrix material is Al alloy and Al2O3 short fiber is reinforcement, volume fractions of Al2O3 short fiber is 10, 15 and 20 %. Manufacture by a low-pressure infiltration method. And the performance is evaluated by microstructure observation, porosity ratio and relative density. It is found that the porosity ratio can be effectively adjusted by the infiltration temperatures and the loads of Al2O3 short-fibres, exhibiting a minimum of 2 for 10% loading at 700°C. Meanwhile, the relative density of composites reached to be a maximum of 98% for 15% loading at 700°C. The low porosity ratio and high density of composites are reasonably attributed to the proper processing techniques.
Authors: Yong Bum Choi, Jae Woong Jung, Won Jo Park, Sun Chul Huh, Kwang Yong Lee, Han Ki Yoon, Gen Sasaki
Abstract: 20 vol.% aluminum borate whisker (Al18B4O33w) reinforced AC4CH alloy composite was fabricated by squeeze casting method. The matrix is controlled its impurities, which make metal alloys, especially AC4CH alloy that is made by restraining 0.2% Iron and aluminum to make a matrix material. The perform of composite materials was made from Al18B4O33w with 5% regulated three kinds of inorganic binders, SiO2, Al2O3 and TiO2 sol, respectively and then sintered at 1373K. The composites were obtained by squeeze cast infiltration of the molten alloy to the perform. Then it was squeeze casting into the matrix. The status of adhesions of whisker perform was Observed by SEM. Micro-Vickers hardness and tensile properties at the room temperature were estimated. Al18B4O33w/AC4CH composites containing TiO2 sol has excellent properties on tensile properties and micro-vickers hardness compared with the other composites without inorganic binder, containing SiO2 and Al2O3 sol inorganic binder.
Authors: Han Ki Yoon, Dong Hyun Kim, Won Jo Park, Akira Kohyama
Abstract: In order to apply a reduced activation ferritic (JLF-1) steel to the blanket/first-wall structure of a fusion reactor, its fracture toughness is very important for the strict estimation of material life. Fracture toughness testing of irradiated materials requires the use of miniaturised specimens and evaluation of TIG welding (tungsten inert gas arc welding) weldment properties is an important issue because necessary for production of nuclear fusion reactors. In this study, the fracture toughness tests were carried out according to the ASTM E1820-99. It was performed on various sizes (ligament and thickness) and various side-grooves of specimens and the TIG welding joint of JLF-1. The test results showed the standard specimen with side-groove of 40% represented valid fracture toughness. Fracture resistance curve (R-curve) increased with increasing specimen ligament and decreased with increasing specimen thickness. However, the R-curve of half size specimen was similar to that of the standard (1inch thickness) specimen. The fracture toughness test results of the TIG welded specimen showed a slight increase in the TIG welded specimen compared with JLF-1 base metal specimen.
Authors: Hua Wei Rong, Cheol Hong Park, Won Jo Park, Han Ki Yoon
Abstract: With the rapid development of aerospace and automobile industries, metal matrix composites (MMCs) have attracted much attention because of its excellent performance. In this paper, Ni-Cr/AC8A composites reinforced with porous Ni-Cr preform were manufactured by low pressure infiltration process, infiltration temperatures are 700oC~850oC. The microstructure and phase composition of composites were evaluated using optical microscope, X-ray diffraction (XRD) and electro-probe microanalysis (EPMA), It's found that they're intermetallic compounds generated in the composites. Recently, intermetallic compounds have attracted much attention as high-temperature material. We study the hardness of Ni-Cr/AC8A composites, the results show the Ni-Cr/AC8A composite has high hardness due to the intermetallic compounds exist.
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