• 한국항공우주학회지
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• 제31권3호
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• pp.15-22
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• 2003

피로균열성장모델을 유도하고 지연모델을 제안하였다. 피로균열성장모델은 피로균열선단의 소성변형으로 인하여 균열표면에 발생하는 잔류소성스트레치를 고려하고 있다. 균열 성장률은 균열선단 재료요소의 소성변형에너지와 누적피로손상으로부터 계산된다. 유도한 균열성장모델로부터 계산한 균열성장률은 AL6061-T651과 17-4PH 주강의 시험결과와 잘 일치하고 있다. 피로균열성장지연모델은 인장과대하중으로부터 생성된 잔류소성스트레치를 근거로 하고 있으며, 인장과대하중은 다음 하중 사이클의 소성변형률을 감소시킨다. Strip-yield모델을 이용하여 균열선단의 소성역을 계산하였다. 새로 제안된 지연모델은 인장과대하중하의 피로균열선장특성 및 지체지연 현상을 잘 기술하고 있다.

• 한국기계가공학회지
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• 제10권4호
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• pp.57-63
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• 2011

The aim of this study is to analyze turning process using commercial FEM simulation code. Various simulation models of orthogonal cutting process for 3 layers of metallic material have been simulated and analyzed. The workpiece material used for the orthogonal plane-strain metal cutting simulation consists of three layers, which are Allow Tool Steel, Aluminum and Stainless Steel. The finite element model is composed of a deformable workpiece and a rigid tool. The tool penetrates through the workpiece at a constant speed and constant feed rate. As an analytical result, detailed cutting temperature, strain, pressure, residual stress for both a tool and each layer of workpiece were obtained during the turning process. It has been closely observed that the chip flow curve deforms continuously.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.37-41
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• 2003

In this study the mechanical behaviors of fiber metal laminates (FML) such as ARALL, GLARE and CARE which are recently developed as new structural materials and known to have excellent fatigue resistant characteristics while with relatively low densities compared to the conventional aluminum materials, are considered through the classical lamination theory. The mechanical properties such as elastic moduli, thermal expansion coefficients and hygro-thermally induced residual stresses in the fiber metal laminates are obtained and compared each other. Also load carrying mechanism between metal sheets and composite layers in the FML are considered.

• 한국전기전자재료학회논문지
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• 제11권7호
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• pp.517-521
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• 1998

After etching Al-Cu alloy films using $SiCl_4/Cl_2/He/CHF_3$ plasma, a corrosion phenomenon on the metal surface has been studied with XPS(X-ray pheotoelectron spectroscopy) and SEM (Scanning electron microscopy). In Al-Cu alloy system, the corrosion occurs rapidly on the etched surface by residual chlorine atoms. To prevent the corrosion, $CHF_3$ plasma treatment subsequent to the etch has been carried put. A passivation layer is formed by fluorine-related compounds on the etched Al-Cu surface after $CHF_3$ treatment, and the layer suppresses effectively the corrosion on the surface as the $CHF_3$treatment in the pressure of 300m Torr.

• 한국해양공학회지
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• 제23권4호
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• pp.1-5
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• 2009

A dilatometer was used to investigate the effect of cure conditions, mold types and the presence of filler in an epoxy system. These studies showed shrinkage in the cured epoxy when heating it through the glass transition temperature region. The magnitude of the shrinkage, related to stress build up in the epoxy during curing, was influenced by the processing conditions, filler presence and the nature of the mold used to contain the resin. Cure and cyclic cure at a lower temperature, prior to a post cure, decreased the magnitude of observed shrinkage. Cure shrinkage decreased with the number of cyclic cures. Post cured samples outside the mold led to less shrinkage compared with samples in the mold. Sample cured in a silicon mold represented less shrinkage than sample cured in an aluminum mold. Sample containing kaolin filler showed less shrinkage than unfilled sample.

• 한국세라믹학회지
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• 제26권3호
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• pp.361-370
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• 1989

Mullite powders were synthesized from the common solution of aluminum sulfate and sodium silicate solutions by the emulsion-hot kerosene technique. The reaction temperature and mechanism for mullitization and the characteristics of synthesized mullite powders were investigated. The effect of Na components introduced from sodium silicate solution on the physical property and microstructure of sintered mullite was also examined. It was proved that mullites were formed at 75$0^{\circ}C$ through the reaction mechanism of Na2O.2.2SiO2＋3.3Al2(SO4)3longrightarrow1.1(3Al2O3.2SiO2)＋Na2SO4＋8.9SO3. Synthetic mullite powders consisted of the compositiion of 3Al2O3.2SiO2 and showed highly agglomeration of hollow spherical particles of 1${\mu}{\textrm}{m}$ diameter. The density and fracture toughness of sintered mullites were somewhat reduced because of the effect of a very small amount of residual Na components.

• 대한기계학회논문집A
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• 제28권4호
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• pp.394-401
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• 2004

In this study the mechanical behaviors of fiber metal laminates(FMLs) such as ARALL, GLARE and CARE which are recently developed as new structural materials and known to have excellent fatigue resistant characteristics while with relatively low densities compared to the conventional aluminum materials, are considered through the classical lamination theory. The mechanical properties such as elastic moduli, thermal expansion coefficients and hygro-thermally induced residual stresses in the fiber metal laminates are obtained and compared each other. Also, carpet plots of effective elastic moduli, Poisson's ratio and the thermal expansion coefficient for GLARE FML are plotted.

• 대한환경공학회지
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• 제32권5호
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• pp.469-476
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• 2010

상수원수의 특성 변화와 갈수기 조류 발생으로 인한 원수 pH 상승 시기에 이산화탄소($CO_2$)를 주입하여 원수 pH를 조정함으로써 혼화·응집지의 응집 효율을 향상시켜 생산 정수 중의 잔류알루미늄, 탁도, 입자수 등의 농도를 낮추는 방법을 조사하고자 본 연구를 실시하였다. 원수 pH 8.0 이상이며 밤 낮의 pH 변화가 크지 않은 2월, 3월, 4월, 12월 중에 이산화탄소 주입 전 후의 정수 수질 변화를 고찰하였으며, 정수처리 공정수를 대상으로 정수 수질평가와 밀접한 관련이 있는 알루미늄, 탁도, 입자수, TOC, THMs, 2-MIB, geosmin 등의 농도 변화를 조사하였다. 조사결과, 혼화 응집지의 응집 효율 향상으로 입자수, 탁도, 알루미늄과 같은 입자성 물질과 무기물질은 감소하였으며 서울시 정수 목표수질값인 입자수 30개/mL 이하, 탁도 0.05 NTU 이하, 알루미늄 0.02 mg/L 이하의 양호한 정수 수질을 유지하기 위해서는 원수 pH 상승시기 이산화탄소를 주입하여 착수정원수 pH를 7.4 이하로 유지해야 하는 것으로 나타났다. 또한 THMs, CH, HAAs, HANs 등 소독부산물과 이취미 유발물질인 2-MIB, geosmin 농도는 원수 pH 변화와 무관함을 알 수 있었으며, 특히 이취미 유발물질인 2-MIB, geosmin는 pH 변화보다는 원수 중의 2-MIB, geosmin 농도가 정수 중의 농도 결정에 주요한 영향을 주는 것으로 나타났다.

• 한국자기학회지
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• 제14권4호
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• pp.143-148
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• 2004

가스관의 비파괴검사로 가장 널리 사용되고 있는 자속누설탈사에서 가스배관의 잔류자화(residual magnetization, $M_{res}$)와 탐사횟수가 누설자속에 미치는 영향을 정량적으로 간편하게 실험실에서 해석할 수 있도록 배관대신에 소형의 모의장치를 제작하여 조사하였다. 제작된 장치는 나사에 의한 결함까지도 측정할 수 있고 또 원형 링을 완벽히 탈자시킬 수 있어 탐사가 진행됨에 따라 잔류자화의 영향, 배관의 자화상태변화와 누설자속 등을 효과적으로 모사할 수 있었다. 탐사횟수가 증가할수록 잔류자화, 최대자속밀도 그리고 검출전압은 감소하다가 일정해지지만 초기잔류자화(initial $M_{res}$)가 커지면 최종잔류자화(final $M_{res}$)도 커졌다. 탐사조건이 일정할 경우 검출전압은 배관의 최대자속밀도보다는 직전의 잔류자화의 크기에 직선적으로 비례하였으며 이것은 탄소강으로 만들어진 원형 링의 자기이력현상, 즉 자구구조의 변화 때문에 생기는 것으로 정확한 탐사신호를 해석하기 위해서는 이력현상을 고찰할 필요가 있다. 또 잔류자화가 크면 첫 번째 탐사에서 높은 검출전압을 얻을 수 있다는 것을 착안하여 두 번째 탐사에서는 착자기의 자화방향을 바꾸면 높은 검출을 얻을 수 있음을 제안하였다.

• 대한기계학회논문집A
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• 제26권2호
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• pp.387-398
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• 2002

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/㎥. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although the former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern. It was revealed that the performance of antenna was related to the impact damage and there was a threshold that the performance of antenna fell as impact energy level changed. The threshold was between the impact energies of 1.5J and 1.75J.