본 연구에서는 유기용매에 저항성이 뛰어난 소재인 polyketone 고분자를 사용하여 열유도 상분리법(TIPS)으로 유기용매 저항성 중공사 분리막을 제조하였다. 희석제는 green solvent로 알려진 PEG300, DMSO2, glycerine을 사용하였으며, 이때 사용된 diluent에 따라 나타나는 구정형 구조를 가지는 고-액 상분리와 bicontinuous한 구조를 가지는 액-액 상분리를 관 찰하였다. 전반적인 분리막의 특성은 SEM, 수투과도, 기계적 강도, 내화학실험을 사용하여 고찰하였으며, 본 연구에서는 다양한 희석제가 적용된 polyketone 중공사 분리막의 제조와 그 상호관계에 대해 심도 있게 연구하였다.

이 연구는 탄소섬유시트의 보강겹수와 보강위치에 따른 I형 PFRP 휨부재의 휨보강 효과에 대해 조사하였다. 또한, 탄소섬유시트로 보강한 PFRP 휨부재의 실험적, 이론적으로 확인하기 위해 유한요소해석을 실시하였으며, 휨실험 결과와 이론적 해석결과를 비교분석하였다. 휨실험 결과와 유한요소해석 결과는 이론적인 결과와 비교한 결과 일치하는 경향을 보였고, 휨보강 효과가 큰 탄소섬유시트 2겹을 보강한 시편에서 결과에서 오차가 가장 크게 발생하였다.

취성특성을 가진 탄소섬유복합체의 인장특성을 결정하기 위해 ASTM D 3 0 39에 따라 인장시험을 실시하였다. 극한시 점에 박리, 부분파단으로 인해 스트레인 게이지의 계측값의 변동성이 커져 신뢰성을 확보하기 어렵기 때문에 극한응력과 탄성 계수를 이용한 유효극한변형률을 제안하고, 극한계측변형률과 상호보완하였다. 특히 게이지가 비정상적으로 작용할 경우에도 적용이 가능하다는 장점이 있다. 또한 유효극한변형률을 결정하는 탄성계수는 단일시편에서 여러 변형률 구간에 대하여 평가하여 비교 검증할 수 있다.

A laser scabbling experiment was performed using a high-power fiber laser to investigate the removal rate of the concrete block and the scabbled depth. Concrete specimens with a 28-day compressive strength of 30 MPa were used in this study. Initially, we conducted the scabbling experiment under a stationary laser beam condition to determine the optimum scan speed. The laser interaction time with the concrete surface varied between 3 s and 40 s. The degree of spalling and vitrification on the surface was primarily dependent on the laser interaction time and beam power. Furthermore, thermal images were captured to investigate the spatial and temporal distribution of temperature during the scabbling process. Based on the experimental results, the scan speed at which the optical head moved over the concrete was set to be 300 mm∙min−1 or 600 mm∙min−1 for the 4.8-kW or 6.8-kW laser beam, respectively. The spalling rates and average depth on the concrete blocks were measured to be 87 cm3∙min−1 or 227 cm3∙min−1 and 6.9 mm or 9.8 mm with the 4.8-kW or 6.8-kW laser beams, respectively.

The use of recycled materials, such as the fine recycled aggregate made from concrete waste and carbon fiber (CF) product of industrial waste, for the manufacture of conductive recycled mortars (CRM), transforms the mortar base cement normally made with cement:sand in a sustainable multifunctional material, conferring satisfactory mechanical and electrical properties for non-structural uses. This action provides ecological benefits, reducing the use of natural fine aggregates from rivers and the amount of concrete waste deposited in landfills resulting from construction waste. In this investigation the effect of the addition of CF on electrical properties in hardened, wet and dry state, electric percolation in dry state and fluidity of the wet mixture of a cement based CRM was evaluated: fine recycled aggregate: graphite powder, CRM specimens with dimensions of 4 × 4 × 16 cm. were manufactured for 3, 7 and 28 days of age and sand/cement ratios = 1.00, graphite/cement = 1.00, water/cement = 0.60 and CF = 0.1, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% compared to the weight of cement. The results demonstrated the effect of the addition of CF in CRM, reducing fluidity of the mixtures due to the opposition generated by its physical interaction of CF with recycled sand or recycled fine aggregate and graphite powder (GP), in its case, placing the electric percolation percolation at 0.30% and 0.45% of CF for CRM with and without GP, respectively. Increases in electrical conductivity (EC) without the presence of GP are defined by the contact between the CF and the conductive paths formed. In contrast, with the presence of GP, the EC is defined by the contact between the CF and the GP simultaneously, forming conductive routes with greater performance in its EC.

Graphene fiber is considered as a potential material for wearable applications owing to its lightness, flexibility, and high electrical conductivity. After the graphene oxide (GO) solution in the liquid crystal state is assembled into GO fiber through wet spinning, the reduced graphene oxide (rGO) fiber is obtained through a reduction process. In order to further improve the electrical conductivity, herein, we report N, P, and S doped rGO fibers through a facile vacuum diffusion process. The precursors of heteroatoms such as melamine, red phosphorus, and sulfur powders were used through a vacuum diffusion process. The resulting N, P, and S doped rGO fibers with atomic% of 6.52, 4.43 and 2.06% achieved the higher electrical conductivities compared to that of rGO fiber while preserving the fibrious morphology. In particular, N doped rGO fiber achieved the highest conductivity of 1.11 × 104 S m−1, which is 2.44 times greater than that of pristine rGO fiber. The heteroatom doping of rGO fiber through a vacuum diffusion process is facile to improve the electrical conductivity while maintaining the original structure.

Due to stricter environmental regulations of the International Maritime Organization (IMO), the number of ships fueled by Liquefied Natural Gas (LNG) is rapidly increasing. The International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) limits the material of tanks that can store cryogenic substances such as LNG. Among the materials listed in the IGC Code, ASTM A553M-17 has been recently adopted as a material for LNG fuel tank projects because of its excellent mechanical properties at cryogenic temperatures. In shipyards, this material is being used to build tanks through Flux Cored Arc Welding (FCAW). However, there is a problem that magnetization occurs during welding and there is a big difference in welding quality depending on the welding position. In order to overcome this problem, this study intends to conduct basic research to apply laser welding to ASTM A553M-17 material. As a result of analyzing the bead shape according to laser BOP speed and Energy density performed in this study, it was confirmed that the penetration and energy density are proportional but the penetration and BOP speed are inverse proportional to some extent. In addition, a range of suitable welding speed and energy density were proposed for the 6.1mm thickness material performed in this study.

In recent, fiber-reinforced composites have been widely used in many fields because of their excellent performance. In order to manufacture lightweight, high-performance, and inexpensive composites various laminated structures were designed. Six types of hybrid composites were fabricated with glass/basalt/aramid fibers by VARTM process. The effect of the laminated structure on the mechanical properties of composites was investigated through impact energy, tensile and bending strength. Compared to other conditions more higher impact energy was obtained when the aramid fibers were in the center position and more higher bending strength was obtained when the fibers are laminated in the order of increasing bending performance from top to bottom. The laminate structure did not affect tensile strength which mainly depends on the property of fibers.

Due to stricter environmental regulations of the International Maritime Organization (IMO), the number of ships fueled by Liquefied Natural Gas (LNG) is rapidly increasing. The International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) limits the material of tanks that can store cryogenic substances such as LNG. Among the materials listed in the IGC Code, ASTM A553M-17 has been recently adopted as a material for LNG fuel tank projects because of its excellent mechanical properties at cryogenic temperatures. In shipyards, this material is being used to build tanks through Flux Cored Arc Welding (FCAW). However, there is a problem that magnetization occurs during welding and there is a big difference in welding quality depending on the welding position. In order to overcome this problem, this study intends to conduct basic research to apply laser welding to ASTM A553M-17 material. In Part I, the bead shape according to the welding output was analyzed and in PART II, ​​the penetration phenomenon according to the welding speed was analyzed after Bead on Plate (BOP) test. As a result of analyzing the bead shape according to laser power performed in this study, it was confirmed that the laser power and penetration depth are proportional to some extent. In addition, a range of suitable welding power was proposed for the 6.1mm thickness material performed in this study.

The multi-layered heat source model is a model that can cover most of existing studies and can be defined with a simple formula. Based on the methodology performed in previous studies, the welding heat source was found through experiments and FEM under the welding power conditions of three cases and the parameters of the welding heat source were analyzed according to the welding power. In this study, parameters of fiber laser welding heat source according to welding power were searched through optimization algorithm and finite element analysis, and the correlation was analyzed. It was confirmed that the concentration of the welding heat source in the 1st layer was high regardless of the welding power, and it was confirmed that the concentration of the welding heat source in the 5th layer (last layer) increased as the welding power increased. This reflects the shape of the weld bead that appears during actual fiber laser welding, and it was confirmed that this study represents the actual phenomenon.

본 연구에서는 Aramid FRP와 모서리보강재로 구속한 엔지니어링플라스틱 보강을 통해 기둥의 횡구속 능력을 증대하여 콘크리트 피복 및 압괴 파괴를 지연시킴으로써 휨 항복 후 연성거동을 유도하여 기존 저층 필로티 건축물의 내진 성능을 확보하는 방법을 제시하고 저층 필로티 건축물의 내진취약요인을 분석하여 필요한 전단보강량을 산정, 제안공법의 목표전단보강을 설정하는 것을 목적으로 한다. 엔지니어링플라스틱을 활용한 기둥의 전단보강형상을 제안하고 필로티 구조의 내진취약요인 보강임계점 예측과 예제모델의 구조해석을 통해 제안공법의 목표전단보강량을 검증하였다. 구조해석 결과, 특별지진하중 적용 시, 휨-축력 내력 초과비율이 타 유형군에 비해 낮은 ST-A1(1축편심)을 기준으로 연면적 750m² 이하와 1축 편심 중심-강심편심율 18%이하에 해당될 경우에는 본 논문에서 제안하는 ‘고성능 복합섬유 패널 전단 보강법’을 적용할 수 있는 경계로 제한하고자 한다.

유리섬유 또는 바잘트섬유로 만들어진 고성능 복합섬유 패널은 고강도 보강재이지만, 구조보강을 위해 정사각형 또는 직사각형 구조물에 패널을 부착할 경우에 일체형 거동을 확보하기 위해 모서리 패널이 사용된다. 이러한 모서리 패널을 이용한 복합섬유 패널의 볼트 접합부를 통해 일체형 거동을 확인하기 위해 실험을 진행하였다. 실험변수로 연단거리 비, 측단거리 비, 볼트 배치 형태(엇모배치와 일렬배치) 및 전단면 수가 설정되었다. 강도평가에 대한 실험 결과, 볼트직경에 대한 연단거리비가 4이상 권장된다는 것을 확인하였고 이를 확보할 시 지압에 의한 파괴모드를 확인하였다. 또한, 볼트배치 2종류의 파괴하중은 값이 유사하였다.

The effect of multi-walled carbon nanotubes (MWCNT) coating in the presence of polyethyleneimine (PEI) of different molecular weights (MW) on the interfacial shear strength (IFSS) of carbon fiber/acrylonitrile–butadiene–styrene (ABS) and carbon fiber/epoxy composites was investigated. The IFSS between the carbon fiber and the polymer was evaluated by means of single fiber microbonding test. The results indicated that uses of the carbon fibers uncoated and coated with pristine, low MW PEI-treated, and high MW PEI-treated MWCNT significantly influenced the IFSS of both thermoplastic and thermosetting carbon fiber composites as well as the carbon fiber surface topography. The incorporation of low MW (about 1300) PEI into the carboxylated MWCNT was more effective not only to uniformly coat the carbon fiber with the MWCNT but also to improve the interfacial bonding strength between the carbon fiber and the polymer than that of high MW (about 25,000) PEI. In addition, carbon fiber/epoxy composite exhibited the IFSS much higher than carbon fiber/ABS composite due to the chemical interactions between the epoxy resin and amine groups existing in the PEI-treated MWCNT.

In this study, gas flow pattern and temperature distribution in a laboratory scale low temperature furnace for carbonization were numerically analyzed. The furnace was designed for testing carbonization process of carbon fibers made from polyimide(PI) precursor. Nitrogen gas was used as a working gas and it was treated as an ideal gas. Three-dimensional computational fluid dynamics analysis for steady state turbulent flow was used to analyze flow pattern and temperature field in the furnace. The results showed that more uniform velocity profile and axisymmetric temperature distribution could be obtained by varying mass flow rate at the inlets.

이 연구는 탄소섬유시트의 보강겹수에 따른 I형 PFRP 휨부재의 휨보강 효과를 조사하기 위해 길이 600mm의 PFRP 휨부재와 상하부 플랜지에 1mm 두께의 탄소섬유시트로 보강하여 휨실험을 수행하였다. 또한, 탄소섬유시트의 보강겹수와 보강 위치에 따른 I형 PFRP 휨부재의 휨보강 효과와 단면 감소량에 대해 조사하였다. 그 결과 2겹으로 보강하였을 때 휨강도와 휨강성이 증가함을 확인하였다.

본 연구의 목적은 형광직물과 재귀반사 소재만으로 제작, 보급되고 있는 현 안전의복에, 광섬유 적용으로 시인성을 높여 야간이나 기상악화 시 안전사고로부터 작업자나 보행자를 보호하는데 있다. 이를 위하여 LED를 촉매로 한 광섬유와, 에너지 하베스팅 기술을 적용하여 설계·제작한 안전조끼를 개발하였다. 안전조끼는 필름에 일체화된 자동 점멸 광섬유에 의해 빛을 방출하도록 설계되었고 이 조끼를 착용한 작업자의 움직임으로, 버려지는 에너지를 수확하 여 광섬유의 발광을 더 지속적으로 구동시키기 위해 에너지 하베스터를 제작하여 부착하였다. 그 결과, 첫째로 조끼 착용자의 신체는 광섬유(optical fiber)와 재귀반사 테이프를 통해 멀리서 인식 가능하도록 시인성이 높아져 사고예방에 도움이 된다. 즉 야간에 실시하는 도로변이나 고지대에서의 작업, 구조대원의 활동, 스포츠 활동 시 사고를 예방하거나, 비상상황이 발생할 경우 광섬유 발광을 변화시키는 신호로 사고 지점을 빨리 발견할 수 있어 인명구조에도 도움이 될 것이다. 둘째, 생활 속 버려지는 에너지를 활용하기 위하여 압전소자 발전 시스템을 개발하여 압전 에너지 하베스팅 장치를 탑재한 결과, 배터리부의 유효 충전량을 활성화하고 보조 충전을 함으로써 에너지를 소량일지라도 효율적으로 생산할 수 있었다. 동시에 안전조끼에 내장하여 제작함으로써 탈착이 용이하도록 하여 활용도를 높였다. 기존 안전 조끼의 경우 야간에 주변 조명이 없을 때는 조끼를 착용한 사람을 인식하는 것이 거의 불가능하지만, 본 연구에서는 안전조끼의 빛 신호로 주변 조명이 없을 때에도 100m 이내에서 착용자를 식별할 수 있었다. 또한 광섬유 적용 안전조끼는 측면에서의 시인성 향상뿐만 아니라 가볍고 (물)세탁이 가능하여 실용적 측면에서 현존하는 LED적용 안전의류보다 우수하다. 그러므로 본 연구에서 개발한, 광섬유와 에너지 하베스터를 장착한 안전조끼는 실용도가 높고 안전사고 발생 예방과 감소, 나아가 인명구조에 이바지할 것으로 추정된다.

In this study, a welding heat source model was presented and verified during fiber laser welding. The multi-layered heat source model is a model that can cover most of existing studies and can be defined with a simple formula. It consists of a total of 12 parameters, and an optimization algorithm was used to find them. As optimization algorithms, adaptive simulated annealing, multi island genetic algorithm, and Hooke-Jeeves technique were applied for comparative analysis. The parameters were found by comparing the temperature distribution when the STS304L was bead on plate welding and the temperature distribution derived through finite element analysis, and all three models were able to derive a model with similar trends. However, there was a deviation between parameters, which was attributed to the many variables. It is expected that a more clear welding heat source model can be derived in subsequent studies by giving a guide to the relational expression and range between variables and increasing the temperature measurement point, which is the target value.