• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.63-66
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• 2000

This research addresses study on thermal residual stress of a composite patch repair of the edge cracked aluminium panel of aging aircraft. Composite patch repair is an efficient and economical technique to improve the damage tolerance of cracked metallic structures. These are thermal residual stresses due to the mismatch of coefficient of thermal expansion, and these are affected by the curing cycle of patch specimen. In this study, three curing cycles were selected for F.E. analysis. This study features the effect on composite patch and aluminum by thermal residual stress during crack propagation in aluminum plate.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.115-118
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• 2000

The development of high-strength fibers such as boron/epoxy and carbon/epoxy and adhesives has made it possible to repair cracked metallic plates by bonding reinforcing patches to the plate over the crack. In this study, aluminum 6061-T6 alloy plates with the high strength are applied to specimens with a cracked bolt hole to study the effect of diverse patch materials on the fatigue behavior of this structure. Additionally, the observation of the effort of different patch sizes on the specimen was performed. The results shows that the patch repair can improve the static strength by about 17% and the fatigue life by 200% compared with non-repaired case. And it was also revealed that the patching method along to crack growth direction is mort efficient in cost and weight reduction.

• Journal of Welding and Joining
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• 제23권6호
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• pp.55-60
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• 2005

In part 1. optimal process parameters such as thickness of stopper and welding time are achieved to produce high strength ISB(Inner Structured and Bonded) panels. Developed process is different from the usual resistance welding process in the number of points welded at a time. In part 2, Numerical modeling for this new process is proposed and the variation of contact area with respect to the gap of electrodes is studied through FE analyses, Besides, it is tried to figure out the welding nugget formation and proper distance between welding points. FE analytic results show that inner structures are melted more than skin plate, and current distribution between points to be welded can be controlled by distance welding points. Comparison of some FE analytic results with corresponding experimental results could confirm the validity of the proposed numerical modeling.

• 한국재료학회지
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• 제12권10호
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• pp.784-790
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• 2002

For mass product of nanocrystalline ZnO ultrafine powders, self-sustaining combustion process(SCP) and ultrasonic spray combustion method(USCM) were applied at the same time. Ultrasonic spray gun was attached on top of the vertical type furnace. The droplet was sprayed into reaction zone of the furnace to form SCP which produces spherical shape with soft agglomerate crystalline ZnO particles. To characterize formed particles, fuel and oxidizing agent for SCP were used glycine and zinc nitrate or zinc hydroxide. Respectively, with changing combustion temperature and mixture ratio of oxidizing agent and fuel, the best ultrasonic spray conditions were obtained. To observe ultrasonic spray effect, two types of powder synthesis processes were compared. One was directly sprayed into furnace from the precursor solution (Type A), the other directly was heated on the hot plate without using spray gun (Type B). Powder obtained by type A was porous sponge shape with heavy agglomeration, but powder obtained using type B was finer primary particle size, spherical shape with weak agglomeration and bigger value of specific surface area. 9/ This can be due to much lower reaction temperature of type B at ignition time than type A. Synthesized nanocrystalline ZnO powders at the best ultrasonic spray conditions have primary particle size in range 20~30nm and specific surface area is about 20m$^2$/g.

• Journal of Microbiology and Biotechnology
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• 제21권2호
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• pp.115-123
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• 2011

To investigate the effects of pipe materials on biofilm accumulation and water quality, an annular reactor with the sample coupons of four pipe materials (steel, copper, stainless steel, and polyvinyl chloride) was operated under hydraulic conditions similar to a real plumbing system for 15 months. The bacterial concentrations were substantially increased in the steel and copper reactors with progression of corrosion, whereas those in stainless steel (STS) and polyvinyl chloride (PVC) reactors were affected mainly by water temperature. The heterotrophic plate count (HPC) of biofilms was about 100 times higher on steel pipe than other pipes throughout the experiment, with the STS pipe showing the lowest bacterial number at the end of the operation. Analysis of the 16S rDNA sequences of 176 cultivated isolates revealed that 66.5% was Proteobacteria and the others included unclassified bacteria, Actinobacteria, and Bacilli. Regardless of the pipe materials, Sphingomonas was the predominant species in all biofilms. PCR-DGGE analysis showed that steel pipe exhibited the highest bacterial diversity among the metallic pipes, and the DGGE profile of biofilm on PVC showed three additional bands not detected from the profiles of the metallic materials. Environmental scanning electron microscopy showed that corrosion level and biofilm accumulation were the least in the STS coupon. These results suggest that the STS pipe is the best material for plumbing systems in terms of the microbiological aspects of water quality.

• 센서학회지
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• 제7권2호
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• pp.90-96
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• 1998

Cross capacitor 원리를 이용하여 $1.95{\pm}0.5\;mm$ 이하의 미소변위를 비접촉으로 정확하게 측정할 수 있는 새로운 전기용량 센서를 설계 제작하였다. 전극의 구조는 센서와 측정 대상체가 각각 하나의 전극으로 작용하여야 하는 기존의 2-전극형 및 3-전극형 센서들이 지니고 있는 단점을 보완하기 위하여 2개의 전극(high, low전극)을 센서의 면에 형성한 4-전극형 센서로 제작하였다. 센서의 전극은 직경 17 mm 두께 0.7 mm인 사파이어 평행원판위에 구리를 사용하여 전극간 간격유지를 0.2 mm로 일정하게 함과 동시에 완전대칭을 이루도록 제작하였다. 따라서 이 센서는 측정대상체가 금속, 비금속에 관계없이 센서와 측정대상체와의 미소변위 및 간격을 측정 할 수가 있다. 측정범위 $1.95{\pm}0.5\;mm$에서의 correlation coefficient는 0.9987, $1.95{\pm}0.25\;mm$에서는 0.9995로 측정되었다.

• 에너지공학
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• 제24권1호
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• pp.78-87
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• 2015

중대사고시 금속용융물층의 열속 집중 현상(Focusig effect)에 대해 상부와 측면벽의 냉각 조건과 높이를 변화시키면서 실험과 수치해석을 수행하였다. 상사성(Analogy) 원리를 이용해 열전달 실험 대신 물질전달 실험을 수행하였으며 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였다. $Ra_H$ 수 $8.49{\times}10^7{\sim}5.43{\times}10^9$ 범위에서 상부와 측면벽의 냉각 조건을 세 가지로, 높이를 네 가지로 변화시키면서 열전달을 측정하였다. 상부만 냉각인 경우의 실험결과를 동일한 조건인 Rayleigh-Benard 자연대류 상관식과 비교한 바 Dropkin과 Somerscales, Globe와 Dropkin의 상관식과 매우 일치하였다. 측면벽만 냉각인 경우, 상부와 측면벽 모두 냉각인 경우, 상부만 냉각인 경우 순으로 열전달이 감소하였고, 냉각 조건을 고정한 상태에서 높이를 감소시킬수록 측면 열전달이 향상되었다.

• Journal of Welding and Joining
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• 제23권6호
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• pp.49-54
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• 2005

Inner Structured and Bonded(ISB) panel, a kind of metallic sandwich panel, consists of two thin skin plates bonded to a micro-patterned inner structure. Its overall thickness is $1\~3mm$and it has attractive properties such as ultra-lightweight, high efficiency in stiffness-to-weight and strength-to-weight ratio. In many previous studies, resistance welding, brazing and adhesive bonding are studied for joining the panel. However these methods did not consider productivity, but focused on structural characteristics of joined panels, so that the joining process is very complicated and expensive. In this paper, a new joining process with resistance welding is developed. Curved surface electrodes are used to consider the productivity and the stopper is used between electrodes during welding time to maintain the shape of inner structure. Welding time, gap of electrodes and distance between welding points are selected as the process parameters. By measuring the tensile load with respect to the variation of welding time and gap of electrodes, proper welding conditions are studied. Welding time is proper between 1.5-2.5cycle. If welding time is too long, then inner structures are damaged by overheating. Gap of electrode should be shorter than threshold value fur joint strength, when total thickness of inner structure and skin plate is 3.3mm, the threshold distance is 3.0mm.

• Corrosion Science and Technology
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• 제20권6호
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• pp.451-465
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• 2021

In this investigation, electrochemical characteristics and damage behavior of 316L stainless steel polymer electrolyte membrane fuel cell(PEMFC) were analyzed by potentiodynamic and potentiostatic tests in cathode operating condition of PEMFC. As the result of potentiodynamic polarization test, range of passive region was larger than range of active region. In the result of potentiostatic test, damage depth and width, pit volume, and surface roughness were increased 1.57, 1.27, 2.48, and 1.34 times, respectively, at 1.2 V compared to 0.6 V at 24 hours. Also, as a result of linear regression analysis of damage depth and width graph, trend lines of damage depth and width according to applied potentials were 16.6 and 14.3 times larger, respectively. This demonstrated that applied potential had a greater effect on pitting damage depth of 316L stainless steel. The damage tendency values were 0.329 at 6 hours and 0.633 at 24 hours with applied potentials, representing rapid growth in depth direction according to the test times and applied potentials. Scanning electron microscopy images revealed that surface of specimen exhibited clear pitting damage with test times and applied potentials, which was thought to be because a stable oxide film was formed by Cr and Mo.

• 한국초전도ㆍ저온공학회논문지
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• 제8권1호
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• pp.9-14
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• 2006

Sample preparation plays a critical role in microstructure analysis using TEM. Although TEM specimen has been usually prepared by jet-polishing or Ar-ion beam milling technique. these methods could not be applied to YBCO CC which is composed of IBAD or RABiTS substrates, several buffet layers, and YBCO superconducting layer because of big difference in mechanical strengths between the metallic phase and oxide phases. To obtain useful cross-sectional information such as interface between the phases or second phases in YBCO CC, it is prerequisite to secure the large area of thin section in the cross-sectional direction. The superconducting layer or the buffer layers are relatively weak and fragile compared to the metallic substrate such as Ni-5wt%W RABiTS of Hastelloy-based IBAD, and preferential removal of weak ceramic phases during polishing steps makes specimen preparation almost impossible. Tripod polisher and small jig were home-made and employed to sample preparation. The polishing angle was maintained <$1^{\circ}$ throughout the polishing steps using 2 micrometers attached to the tripod plate. TEM specimens with large and thin area could be secured and used for RABiTS/IBAD substrate analyses. In some cases, additional Ar-beam ion milling with low beam current and impinging angle was used for less than 30 sec. to remove debris or polishing media attacked to the specimens.