• Journal of Welding and Joining
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• 제31권5호
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• pp.47-53
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• 2013

We have investigated the traits of clad metals in hot-rolled clad steel plates, including the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516), under various specific circumstances regarding post heat treatment, multilayered welds, and thick or repeated welds for repair. For evaluations, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by micro vickers hardness, tensile, and etching tests the results were compared with those of EPR tests. The clad steel plates were butt-welded using FCAW and SAW with the time of heat treatment as the variable, a that was conducted at $625^{\circ}C$, for 80, 160, 320, 640, and 1280 min. Then, the change in corrosion resistance was evaluated in these specimens. With carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro-hardness gradually increased and decreased after 640 min. The elongation and contraction of the area also increased gradually. The oxalic acid etch test and EPR test on STS316 and the clad metal showed STEP structure and no sensitization. From the test results on multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. The purpose of this study was to suggest some considerations for developing on-site techniques to evaluate the sensitization of stainless steels.

• 대한기계학회논문집A
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• 제35권12호
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• pp.1655-1662
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• 2011

본 연구는 레이저를 이용한 스테인리스강의 용접성 평가에 대한 연구이다. 사용된 금속인 스테인리스 스틸은 녹 및 열적변형이 우수하여 다양한 적용 분야를 가지고 있다. 본 연구는 50 W 레이저 열원에 자기장을 적용하여 스테인리스 스틸에 기계적 성질을 향상 시키는데 목적을 두고 있다. 이에 따른 기계적 성질을 분석하기 위하여 수치적 해석, 인장강도, 형상 및 미세조직, 경도 시험 등을 수행하였다. 결과적으로 수치적 해석을 통한 금속 용융점에서의 속도 증가, 인장강도 약 16 MPa 상승, 용융부에 섞임, 경도 약 7 Hv 상승으로 기계적 성질이 향상 되었다.

• 한국방재안전학회논문집
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• 제11권2호
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• pp.17-28
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• 2018

본 연구에서는 지반굴착 시 굴착구간 주변의 지하시설물이 지하수 흐름특성에 미치는 영향을 파악하기 위해 지하시설물의 규모와 이격거리, 지하수 동수구배 등을 고려하여 시나리오 기반으로 굴착 단계별 지하시설물의 영향을 지하수 수위 변화와 지하수 유출량 측면에서 비교 분석하였다. 그 결과 지하시설물의 규모가 증가할수록 수두차와 수두구배가 크게 발생하며 이격거리가 짧을수록 큰 수두차와 수두구배를 보인다. 모델영역의 지하수 수두구배에 따른 영향은 비교적 작은 것으로 나타났다. 또한 시나리오에 대한 지하수 유출량 분석 결과 지하시설물의 규모가 증가하거나 이격거리가 짧을수록 지하수 유출량이 감소하는 경향을 보인다. 이는 지반굴착에 따른 지하수 유동특성 분석에 있어 주변에 존재하는 지하시설물에 대한 영향 검토가 필요한 것으로 판단된다.

• 의료ㆍ복지 건축 : 한국의료복지건축학회 논문집
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• 제27권2호
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• pp.15-24
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• 2021

Purpose: This study is to present basic data on the Architectural planning of the college of medicine by arranging the functional zoning planning, functional unit planning, and circulation planning, based on the diversification of medical education and the changes of Learning spaces. Methods: This study was conducted by literature review on existing medical education method and learning space planning. And then on-site surveys and questionnaire were conducted on existing facilities. Results: The diversification of medical education has already been progressing for a long time, and the development of information technology is integrated into the learning space, and the evolution of the learning method and the flexibility of the learning space give effect to the change of the learning space. ① This study reconstructed the existing classification method of university facilities into the fuctional zoning method that combines the architectural concept of function and movement. ② The functions and functional units of the college of medicine according to the proposed functional zone were arranged, and the space required for the medical college was suggested. ③ The function and type of movement of medical college can be classified into professor/student fusion type, teaching and research separation type, and learning and learning shared space integrated arrangement type. In the future, it is necessary to consider fusion type or integrated arrangement type rather than separation type. Implications: the evolution of the learning method and the flexibility of the learning space give effect to the change of the learning space.

• 비파괴검사학회지
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• 제29권5호
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• pp.473-478
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• 2009

본 연구에서는 비파괴법을 이용하여 압력용기 강 다층용접부에서 채취한 표준 샤르피 시험편의 균열선단에서 형성되는 소성변형 거동을 평가하였다. 모재, 후열처리재 및 용접재를 대상으로 시험편에 기계적인 노치를 가공한 후 예균열(pre-crack)을 낸 다음 4점 굽힘실험과 음향방출(acoustic emission: AE)실험을 동시에 실시하였다. 균열선단은 용접재외 후열처리재의 경우 용융선 근처에 위치하도록 하였다. 하중이 가해짐에 따라 균열선단에서 형성되는 소성영역의 크기는 응력확대계수를 이용하여 구했으며, 각 시험편에 대한 소성역의 크기와 음향방출 특성과의 관계는 축적된 AE 에너지 관점에서 고찰하였다. 시험편에 관계없이 탄성역역에서는 거의 AE신호가 감지되지 않았으며, 대부분의 AE신호는 소성변형 과정에서 발생하였다. 또한, 용접재가 모재와 후열처리재에 비해 AE신호가 훨씬 많이 발생하였다. 모재와 후열처리재 및 용접재의 균열선단에서 소성영역 크기와 축적된 AE에너지와의 관계는 현저히 다르게 나타났으며, 용접재의 AE counts는 모재와 후열처리재에 비해 많이 발생하였다.

• 대한기계학회논문집
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• 제11권5호
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• pp.762-771
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• 1987

본 연구에서는 국산 구조용 강인 SM45C와 SUS304재를 마찰가열압력과 업셋압 력을 서로 변화시키고 업셋시간을 2초로 고정하여 압접시간 10초를 기준으로 하여 변 화시키면서 마찰압접한 후 압접시간 변화에 따른 인장강도의 변화와 업셋량 변화에 따 른 인장강도 및 굽힘강도를 고찰하였다.또 최고 강도치를 나타내는 압접조건을 구 한 후 미소 경도치 및 이종재의 압접부에서 미소하게 변화하는 조직변화도 함께 고찰 하였다.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1997년도 추계학술발표회 논문집
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• pp.45-52
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• 1997

The objective of this study is, with concept of fitness-for-purpose, to evaluate the fracture toughness in X-grooved weld HAZ(heat-affected zone) of QLT(quenching, lamellarizing and tempering)-processed $9\%$ Ni steel, qualitatively and quantitatively, and analyze the relation with the change of microstructure. In general, CTOD test is widely used to determine the fracture toughness of steel weldments. But several problem of accuracy has been brought up. Therefore, in this study, modified CTOD test was used for X-grooved weld HAZ for $9\%$ Ni steel. Additionally, microstructure of HAZ is observed and analyzed by OM, SEM and XRD. From the resulty, HAZ toughness of QLT-$9\%$ Ni steel decreased as the evaluated region approaches the fusion line. The decreased toughness was partly caused by reduction of the retained austenite content, resulted from decreased nucleation site of the retained austenite content, resulted from decreased nucleasion site for reverse transformation due to the increasing fraction of coarse grained region. On the other hand, unexpectedly, the increasing fraction of ductile weld did not increase the HAZ toughness. Therefore, in this X-grooved weld HAZ, the primary factor affecting fracture toughness was the fraction of coarse grained region, i.e., the weakest region.

• 한국의류학회지
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• 제19권1호
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• pp.36-50
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• 1995

The purpose of this study was 1) to estimate the improvement of thermal storage/release and moisture transport properties of PEG-treated acrylic athletic socks and suggest the optimum add-on for PEG treatment, 2) to investigate wear performance of untreated cocks and two kinds of socks treated with PEG of minimum and optimum add-on respectively, and 3) to consider the effect of thermal storage/release and moisture transport properties of PEG- treated socks on the wear performance and the subjective comfort zone. Thermal activities of specimens treated by PDC were evaluated on a DSC by measuring the heat of fusion on heating and the heat of crystallization on cooling. Moisture regain, absorption speed, wickability, water retenti on value, and water-vapor permeability were measured. In the wear trials that the subjects performed a subsequent exercise protocol wearing three differently treated socks in a conditioned environment ($14\pm2^{\circ}C$, 65$\pm$2% R.H.), microclimate temperature and humidity, and subjective wear sensations including thermal sensation, wettedness, softness, fit, and overall comfort were obtained. PEC-treated specimens with more than 20% add-on showed thermal storage on heating and thermal release on cooling by a DSC and the heat contents of treated ones were generally proportional to the add-ons. Moisture transport properties were highly improved after PEG treatment and increased rapidly with increasing add-on. The tendencies were, however, relaxed above 50% add-on and the treated knits were much stiffer above that add-on. In the wear trials of untreated, PEG add-on 20%, and 50% acrylic socks, the changes of microclimate temperature of 50% socks were significantly less than that of 20% socks. PEG add-on 50% socks showed significantly less changes of microclimate humidity than other two kinds of socks. Three kinds of socks showed significant differences in overall comfort and add-on 50% socks were accepted more comfortable than other two kinds of socks. Comfort zone of foot was extended after PEG treatment on socks and it implied that the subjects wearing PEG- treated socks felt comfortable in wider ranges of microclimate temperature and humidity.

• Corrosion Science and Technology
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• 제17권3호
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• pp.109-115
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• 2018

Electrical Resistance Welding (ERW) on a longitudinal seam-welded pipe has been extensively used in oil and gas pipelines. It is well known that the weld zone commonly suffers from grooving corrosion in ERW pipes. In this paper, the grooving corrosion performances of API X65 grade non-sour service (steel-A) and API X70 grade sour gas resistant (steel-B) steel electrical resistance welding pipelines were evaluated. The microstructure of the bondline is composed of coarse polygonal ferrite grains and several elongated pearlites. The elongated pattern is mainly concentrated in the center of the welded area. The grooving corrosion test and electrochemical polarization test were conducted to study the corrosion behavior of the given materials. A V-shaped corrosion groove was found at the center of the fusion zone in both the steel-A and steel-B ERW pipes, as the corrosion rate of the bondlines is higher than that of the base metal. Furthermore, the higher volume fraction of pearlite at the bondline was responsible for the higher corrosion rate at the bondline of both types of steel.

• 한국레이저가공학회지
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• 제10권3호
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• pp.25-32
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• 2007

The effect of welding speed on the weldability, microstructures, hardness, tensile property of Nd:YAG laser welding joint in 600MPa grade precipitation hardening high strength steel was investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5kW. Porosity in the joints occurred at 1.8m/min, but were not observed over the welding speed of 2.1m/min. However, spatter occurred over the welding speed of 6.6m/min. The hardness was the highest at heat affected zone(HAZ) near fusion zone(FZ), and was decreased on approaching to the base metal. The maximum hardness increased with increasing welding speed. The microstructure of FZ was composed of coarse grain boundary ferrite and bainite(upper) but the HAZ near the FZ contained bainite(Lower) and fine ferrite at a low welding speed. With increasing welding speed, ferrite at the FZ and the HAZ became finely and upper binite changed to lower bainite. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal, and the tensile strength and the yield strength of joints was equal to those of raw material. Elongation was found to be lower than that of the raw material.