• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.28-33
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• 2008

This paper presents the characteristics of mechanical properties within the heat affected zones(HAZs) of dissimilar metal weld joint between SA508 Gr.1a and F3l6 stainless steel(SS) with Alloy 82/182 filler metal. Tensile tests were performed using small-size specimens taken from the heat affected regions close to both fusion lines of weld, and the micro-structures were examined using optical microscope(OM) and transmission microscope(TEM). The results showed that significant gradients of the yield stress(YS), ultimate tensile stress(UTS), and elongations were observed within the HAZ of SA508 Gr.1a. This was attributed to the different microstructures within the HAZ developed during the welding process. In the HAZ of F316 SS, however, the welding effect dominated the YS and elongation rather than UTS. TEM micrographs demonstrated these characteristics of the HAZ of F316 SS was associated with a dislocation-induced strain hardening.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.2
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• pp.128-136
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• 2008

It is necessary to estimate the cooling load of the next day for effective control of ice thermal storage system. In this paper, new methodology is proposed to estimate the cooling load using design parameters of building and predicted weather data. Only six input parameters such as sensible heat coefficient and constant, latent heat coefficient and constant, maximum and minimum temperature are necessary to obtain hourly distribution of cooling load for the next day. Two benchmarking buildings(hospital and research institute) are selected to validate the performance of the proposed method, and the estimated cooling loads in hourly and daily bases are calculated and compared with the measured data for E hospital. The estimated results show fairly good agreement with the measured data for both buildings.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.296-300
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• 2018

T-type and H-type section steels were generally used in shipbuilding and offshore plants and were produced by welding technology. These section steels were produced by handwork, and the supplying amounts can't satisfy the demand amounts of the fabrication companies. In case of fillet welding, there are some gaps in weld-joint region due to no groove preparation processing and it can occur crack initiation in the welded region. It is important to evaluate the microstructural and mechanical properties of welded zone to solve these problems. To satisfy the demand amounts of T-bar parts, automatic welding technology was introduced and several conditions as a function of welding speeds were carried out to improve the manufacturing speed. Heat-affected zone may be affected by variation of heat input and cooling rate through automatic welding speed and welding speed is necessary to be optimized. In this study, fusion zone and heat-affected zone were investigated by microstructural and mechanical analysis and were evaluated whether the welded parts were sound or not.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.6
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• pp.1215-1220
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• 2019

Currently, each farm bears both the outbreak of foot-and-mouth disease and the damage caused by AI. In addition, complaints about odors in the livestock industry are constantly being recovered and are expected to occur in the future. The purpose of this study is to improve the indoor air quality of enclosed facilities such as barns, houses, pigsty, and etc. This paper develops low-temperature plasma waste heat ventilation system to be installed in ventilation unit location and standardizes heat exchange element, low-temperature plasma lamp, and ballast for enhanced air cleaning function. In addition, this study intends to develop a new control system so that the farmers can connect with existing weather systems, flow fans, and other facility equipment by incorporating ICT.

• Progress in Superconductivity and Cryogenics
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• v.26 no.2
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• pp.24-30
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• 2024

Metal 3D printing is utilized in various industrial fields due to its advantages, such as fewer restrictions on production shape and reduced production time and cost. Existing research on 3D printing metal materials focused on changes in material properties depending on manufacturing conditions and was mainly conducted in a room temperature environment. In order to apply metal 3D printing products to cryogenic applications, research on the properties of materials in cryogenic environments is necessary but still insufficient. In this study, we evaluate the properties of stainless steel (STS) 316L and CuCr1Zr manufactured by Laser Powder Bed Fusion (LPBF) in a cryogenic environment. CuCr1Zr is a precipitation hardening alloy, and changes in material properties were compared by applying various heat treatment conditions. The mechanical properties of materials manufactured using the LBPF method are evaluated through tensile tests at room temperature and cryogenic temperature (77 K), and the thermal properties are evaluated by deriving the thermal conductivity of CuCr1Zr according to various heat treatment conditions. In a cryogenic environment, the mechanical strength of STS 316L and CuCr1Zr increased by about 150% compared to room temperature, and the thermal conductivity of CuCr1Zr after heat treatment increased by about 6 to 10 times compared to before heat treatment at 40 K.

• Journal of Powder Materials
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• v.30 no.2
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• pp.140-145
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• 2023

Although the Ti-6Al-4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the high degree of design freedom for the geometry of products having outstanding performance used in high-tech applications. In this study, to investigate the effect of bulk shape on the microstructure and mechanical properties of L-PBFed Ti-6Al-4V alloys, two types of samples are fabricated using L-PBF: thick and thin samples. The thick sample exhibits lower strength and higher ductility than the thin sample owing to the larger grain size and lower residual dislocation density of the thick sample because of the heat input during the L-PBF process.

• Journal of Energy Engineering
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• v.14 no.2 s.42
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• pp.153-158
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• 2005

In order to investigate the short-term performance of polyethylene electrofusion joints, the mechanical tests and stress analysis have been conducted to the artificially defected weld joints. The defects of lack of fusion with a square-type were fabricated with 10, 20, 30, 40, 50, 60$\%$ size of the width of heat-ing wire zone, respectively. In this defect sires range, both tensile and bending test results showed the dependence of defect size to the electrofusion joints performance, but both sustained pressure and crush test results didn't. The numerical stress analysis results including the soil and internal pressures, tensile and bend-ing stresses clearly showed the dependence of fusion defect size. Based on both mechanical test and stress analysis results, the maximum acceptable defect size in polyethylene electrofusion joints is discussed.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.54-60
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• 2016

We have investigated the crystallization mechanism of the lithium disilicate ($Li_2O-2SiO_2$, LSO) glass particles with different sizes by isothermal and non-isothermal processes. The LSO glass was fabricated by rapid quenching of melt. X-ray diffraction and differential scanning calorimetry measurements were performed. Different crystallization models of Johnson-Mehl-Avrami, modified Ozawa and Arrhenius were adopted to analyze the thermal measurements. The activation energy E and the Avrami exponent n, which describe a crystallization mechanism, were obtained for three different glass particle sizes. Values of E and n for the glass particle with size under $45{\mu}m$, $75{\sim}106{\mu}m$, and $125{\sim}150{\mu}m$, were 2.28 eV, 2.21 eV, 2.19 eV, and ~1.5 for the isothermal process, respectively. Those values for the non-isothermal process were 2.4 eV, 2.3 eV, 2.2 eV, and ~1.3, for the isothermal process, respectively. The obtained values of the crystallization parameters indicate that the crystallization occurs through the decreasing nucleation rate with a diffusion controlled growth, irrespective to the particle sizes. It is also concluded that the smaller glass particles require the higher heat absorption to be crystallized.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.122-126
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• 2017

The aim of this study was to develop a device for solving the heating problem of living space using heated air, utilizing a simple air heater type collector for solar energy. At the present time, this study assessed the possibility of a development system through theoretical calculations for the amount of available energy according to the size change of the air-heated solar energy collector. To produce and supply hot water using the heat energy of the sun, hot water at $100^{\circ}C$ or less was produced using a flat or vacuum tube type collector. The purpose of this study was to research the air heating type solar collector that utilizes heating energy with heating air above $75^{\circ}C$, by designing and manufacturing an air piping type solar collector that is a simpler type than a conventional solar collector system. The analysis results were obtained for the generated air temperature ($^{\circ}C$) and the production of air (kg/h) to determine the performance of air heating by an air-heated solar collector according to the heat transfer characteristics in the collector of the model when a specified amount of heat flux was dropped into a solar collector of a certain size using PHOENICS, which is a heat flow analysis program applying the Finite Volume Method. From the analysis result, the temperature of the air obtained was approximately $40.5^{\circ}C$, which could be heated using an air heating tube with an inner diameter of 0.1m made of aluminum in a collector with a size of $1.2m{\times}1.1m{\times}0.19m$. The production of air was approximately 161 m3/h. This device can be applied to maintain a suitable environment for human activity using the heat energy of the sun.

• Journal of the Korean Society of Clothing and Textiles
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• v.5 no.1
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• pp.27-30
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• 1981

The change of physical properties of polyester yarn treated with sodium hydroxide solution for making polyester silk like was investigated. The tenacity of polyester yarn was reduced by increasing alkali concentration and temperature. Degree of polymerization of polyester was decreased slightly but the heat of fusion was not changed appreciably.