• Steel and Composite Structures
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• 제18권3호
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• pp.583-601
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• 2015

In the present study, the combined effects of thermal and mechanical loadings on the interlaminar shear stresses of both moderately thin and thick composite laminated beams are numerically analyzed. The finite element modelling of laminated composite beams and analysis of interlaminar stresses are performed using the commercially available software package MSC NASTRAN/PATRAN. The validity of the finite element analysis (FEA) is demonstrated by comparing the experimental test results obtained due to mechanical loadings under the influence of thermal environment with those derived using the present FEA. Various parametric studies are also performed to investigate the effect of thermal loading on interlaminar stresses generated in symmetric, anti-symmetric, asymmetric, unidirectional, cross-ply, and balanced composite laminated beams of different stacking sequences with identical mechanical loadings and various boundary conditions. It is shown that the elevated thermal environment lead to higher interlaminar shear stresses varying with the stacking sequence, length to thickness ratio, ply orientations under identical mechanical loading and boundary conditions of the composite laminated beams. It is realized that the magnitude of the interlaminar stresses along xz plane is always much higher than those of along yz plane irrespective of the ply-orientation, length to thickness ratios and boundary conditions of the composite laminated beams. It is also observed that the effect of thermal environment on the interlaminar shear stresses in carbon-epoxy fiber reinforced composite laminated beams are increasing in the order of symmetric cross-ply laminate, unidirectional laminate, asymmetric cross-ply laminate and anti-symmetric laminate. The interlaminar shear stresses are higher in thinner composite laminated beams compared to that in thicker composite laminated beams under all environmental temperatures irrespective of the laminate stacking sequence, ply-orientation and boundary conditions.

• Structural Engineering and Mechanics
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• 제36권6호
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• pp.759-783
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• 2010

In this paper, compressive strength of carbon fiber reinforced polymer (CFRP) confined concrete cylinders is formulated using a hybrid method coupling genetic programming (GP) and simulated annealing (SA), called GP/SA, and a robust variant of GP, namely multi expression programming (MEP). Straightforward GP/SA and MEP-based prediction equations are derived for the compressive strength of CFRP-wrapped concrete cylinders. The models are constructed using two sets of predictor variables. The first set comprises diameter of concrete cylinder, unconfined concrete strength, tensile strength of CFRP laminate, and total thickness of CFRP layer. The most widely used parameters of unconfined concrete strength and ultimate confinement pressure are included in the second set. The models are developed based on the experimental results obtained from the literature. To verify the applicability of the proposed models, they are employed to estimate the compressive strength of parts of test results that were not included in the modeling process. A sensitivity analysis is carried out to determine the contributions of the parameters affecting the compressive strength. For more verification, a parametric study is carried out and the trends of the results are confirmed via some previous studies. The GP/SA and MEP models are able to predict the ultimate compressive strength with an acceptable level of accuracy. The proposed models perform superior than several CFRP confinement models found in the literature. The derived models are particularly valuable for pre-design purposes.

• 한국재료학회지
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• 제20권1호
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• pp.31-36
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• 2010

Methylene blue (MB) was degraded by $TiO_2$ and ZnO deposited on an activated carbon fiber (ACF) surface under UV light. The ACF/$TiO_2$ and ACF/ZnO composites were characterized by BET, SEM, XRD, and EDX. The BET surface area was related to the adsorption capacity for composites. The SEM results showed that titanium dioxide and zinc oxide are distributed on the ACF surface. The XRD results showed that the ACF/$TiO_2$ and ACF/ZnO composites contained a unique anatase structure for $TiO_2$ and a typical hexagonal phase for ZnO respectively. These EDX spectra showed the presence of peaks of Ti element on ACF/$TiO_2$ composite and peaks of Zn element on the ACF/ZnO composite. The blank experiments for either illuminating the MB solution or the suspension containing ACF/$TiO_2$ or ACF/ZnO in the dark showed that both illumination and the catalyst were necessary for the mineralization of organic dye. Additionally, the ACF/$TiO_2$ composites proved to be efficient photocatalysts due to degradation of MB at higher reaction rates. The addition of an oxidant $([NH_4]_2S_2O_8)$ led to an increase of the degradation rate of MB for ACF/$TiO_2$ and ACF/ZnO composites.

• 한국재료학회지
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• 제3권2호
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• pp.197-204
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• 1993

Plastic기 복합재료의 파괴거동에 미치는 원공크기오 판폭의 영향을 검토하기 위하여 단축인장시험을 행하였다. 점응력파손조건에서의 특성길이 $d_o$는 원공크기 및 판폭에 의존하며, 이를 기초로 파손강도를 예측하기 위한 수정 점응력 파손조건식을 제안하였다. 이 파손조건의 예측값은 실험값과 잘 일치하였다. 파손 강도는 원공선단의 손상비의 증가에 따라 증가하며, 이는 손상영역의 형성으로 인한 응력완화현상으로 설명되어 진다. 또한 불안정 파괴시의 최대균열길이 $a_c$는 특성길이 $d_o$의 약 2배의 값을 나타낸다. 파괴인성에 대응하는 한계에너지해방율 $G_c$의 변화는 원공선단의 손상영역의 증가에 의한 응력완화가 주요한 원인이라고 할 수 있다.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.194-201
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• 2020

Recently, Type 2 high-pressure hydrogen storage tank is studied due to fast defect detection, easy manufacturing, and cost efficiency. Moreover, the dry winding a high-strength metal wire will make increased economic efficiency compare with the wet winding method and the carbon/glass fiber winding method. In this study, a theoretical study on the dry winding of a Type 2 high pressure hydrogen tank using a metal wire was done, and the equations of the total stress on the aligned and the staggered winding for the hoop winding were derived, and the following results were obtained by using these equations. As the diameter of the metal wire, the number of winding layers, and the outer diameter of the liner increase, the maximum stress decreases, but the difference between the maximum stress occurring in the aligned winding and the staggered winding increases. As the pressure increases, the thickness of the winding layer increases, but as the strength of the metal wire increases, the thickness of the winding layer decreases. In addition, regardless of the strength of the metal wire, the thickness of the winding layer of the staggered winding was about 13.4% thinner than that of the aligned winding.

• 한국가스학회지
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• 제23권5호
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• pp.1-7
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• 2019

호흡용 용기에 흠 등의 결함이 발생하였을 때 용기의 잔존강도를 파악하여 파열압력을 판단해야하지만, 복합재료 용기의 경우 흠에 따른 파열 강도의 예측이 어려우며 기법이 복잡하다. 따라서 본 연구에서는 Type-I 용기의 면적용량법 적용 결과를 토대로 Type-III 용기에 결함발생시 파열을 예측하기 위해 면적 용량법 모델을 개발하였으며, 그 신뢰성을 확인하기 위해 용기의 외면에 흠을 가공하여 파열시험을 실시하였다. 면적 용량법 모델의 예측 결과와 실험의 경향이 매우 일치하는 경향을 보였으며, 향후 복합재 용기의 파열압력 추정 방법에 있어 중요한 자료가 될 것으로 기대한다.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.2059-2066
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• 2018

This study explored the feasibility of utilizing an SWCNT-coated fabric sensor for the development of a wearable motion sensing device. The extent of variation in electric resistance of the sensor material was evaluated by varying the fiber composition of the SWCNT-coated base fabrics, attachment methods, number of layers, and sensor width and length. 32 sensors were fabricated by employing different combinations of these variables. Using a custom-built experimental jig, the amount of voltage change in a fabric sensor as a function of the length was measured as the fabric sensors underwent loading-unloading test with induced strains of 30 %, 40 %, and 50 % at a frequency of 0.5 Hz. First-step analysis revealed the following: characteristics of the strain-voltage curves of the fabric sensors confirmed that 14 out of 32 sensors were evaluated as more suitable for measuring human joint movement, as they yield stable resistance values under tension-release conditions; furthermore, significantly stable resistance values were observed at each level of strain. Secondly, we analyzed the averaged maximum, minimum, and standard deviations at various strain levels. From this analysis, it was determined that the two-layer sensor structure and welding attachment method contributed to the improvement of sensing accuracy.

• 한국안전학회지
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• 제31권3호
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• pp.16-21
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• 2016

Carbon Fiber Reinforced Plastic(CFRP) composite with a higher specific strength and rigidity is more excellent than conventional metallic materials or other organic polymer of FRP. It has been widely used in vehicles, aerospaces and high technology industries which are associated with nuclear power fields. However, CFRP laminated composite has several disadvantages as like a delamination, matrix brittleness and anisotropic fibers that are the weak points of the crack initiation. In this present work, the reinforced silicon carbide(SiC) particles were added to the interlayer of CFRP laminates in order to mitigate the physical vulnerability affecting the cracking and breaking of the matrix in the CFRP laminated composite because of excellent specific strength and thermal shock resistance characteristics of SiC. The 1wt% of SiC particles were spread into the CFRP prepreg by using a spray coating method. After that, CFRP prepregs were laminated for the specimen. Also, the twill woven type CFRP prepreg was used because it has excellent workability. Thus the mechanical and fracture behaviors of the twill woven CFRP laminated composite reinforced with SiC particles were investigated with the acoustic emission(AE) method under a fracture test. The results show that the SiC particles enhance the mechanical and fracture characteristics of the twill CFRP laminate composite.

• 한국통신학회논문지
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• 제36권6B호
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• pp.642-649
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• 2011

본 논문은 다중 대역에서 동작하는 안테나를 장착한 차세대 이동통신 기지국 시스템의 도입 가능성 분석을 위해 종래의 기지국 시스템과 케이블 손실전력을 고려한 차세대 기지국 시스템의 전력 손실 및 탄소 절감효과를 분석하였다. 차세대 기지국 시스템은 옥외에 무선처리부를 설치하고, 옥내의 기저대역처리부는 광케이블로 연결하여 종래의 기지국에서 케이블로 인해 발생하는 전력손실을 없애는 구조이다. 본 연구 결과 종래의 기지국과 비교하여 동일한 서비스 커버리지 확보가 가능하고, 케이블 전력손실이 5 dB 줄어든 차세대 기지국 시스템을 도입할 경우 CDMA 20W, WCDMA 30W, WiBro 10W 기지국에서 소모하는 전력량은 연간 155,078 MWh에서 49,038 MWh로 감소시킬 수 있으며, 탄소배출량 또한 65,878 $tCO_2$에서 20,832 $tCO_2$로 절감됨을 확인하였다. 따라서 차세대 기지국 시스템은 그린 IT 기술로 이용 가능할 것으로 고찰되었다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권6호
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• pp.30-36
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• 2018

기존 콘크리트 구조물의 노후화 또는 지진과 같은 외부 하중에 의하여 구조물의 구조 성능이 저하되기 때문에, 기존 건물의 보수 및 보강 연구는 중요하다. 외부부착 탄소섬유 보강 공법과 같은 효율적인 보수 공법을 사용하면 경제적으로 콘크리트 구조물의 구조 성능을 높일 수 있다. 따라서 외부부착 탄소섬유를 사용한 콘크리트 부재의 실험 연구는 많이 진행되었다. 특히, 콘크리트 보를 사용한 전단 보강에 관한 연구는 탄소섬유의 양, 부착 각도, 스트립의 폭, 그리고 재료간의 상호작용에 관한 것이었다. 하지만 선행된 연구에 비하여 탄소섬유의 이 방향 레이아웃에 관한 다양한 변수 연구는 부족한 상황이다. 따라서 이 연구에서는 이 방향 레이아웃 외부부착 탄소섬유 공법을 사용하여 콘크리트 보의 전단보강 효과를 검증하였다. 이 방향 레이아웃의 보강 효과는 스터럽과의 전단 기여도, 실험체의 전단 거동과 보강 시점에 따른 최대 내력의 비교를 통하여 이루어졌다.