• 한국소음진동공학회논문집
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• 제14권7호
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• pp.639-647
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• 2004

This paper concerns the analytical modeling and dynamic analysis of advanced rotating blade structure implemented by a dual approach based on structural tailoring and viscoelastic material technology. Whereas structural tailoring uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The main structure is modeled as a composite thin-walled beam Incorporating a number of nonclassical features such as transverse shear. anisotropy of constituent materials, and rotary inertia etc. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on dynamic response of a thin-walled beam structure exposed to external time-dependent excitation.

• Structural Engineering and Mechanics
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• 제57권5호
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• pp.937-949
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• 2016

Fiber reinforced polymer (FRP) applications in the structural engineering field include concrete-FRP composite systems, where FRP components are either attached to or embedded into concrete structures to improve their structural performance. This paper presents the results of an analytical study conducted using finite element model (FEM) to simulate the behavior of three-points load beam reinforced with GFRP and/or steel bars. To calibrate the FEM, a small-scale experimental program was carried out using six reinforced concrete beams with $200{\times}200mm$ cross section and 1000 mm length cast and tested under three point bending load. The six beams were divided into three groups, each group contained two beams. The first group was a reference beams which was cast without any reinforcement, the second group concrete beams was reinforced using GFRP, and the third group concrete beams was reinforced with steel bars. Nonlinear finite element simulations were executed using ANSYS software package. The difference between the theoretical and experimental results of beams vertical deflection and beams crack shapes were within acceptable degree of accuracy. Parametric study using the calibrated model was carried out to evaluate two parameters (1) effect of number and position of longitudinal main bars on beam behavior; (2) performance of concrete beam with composite longitudinal reinforcement steel and GFRP bars.

• 대한건축학회연합논문집
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• 제21권3호
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• pp.87-92
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• 2019

To relieve noise between floors in Korea, recent domestic and overseas studies have been developing materials that have the properties of ceramic, which is an inorganic compound, and polymer, which is an organic compound, to introduce a new function to polymer. This study conducted a bending strength experiment between re-bar and new composite concrete mixing POSS (Polyhedral Oligomeric Silses-quioxanes) nano complex on the inside of concrete, and by assembling the inside of each concrete with 3 and 4 main re-bars as an experiment to supplement various problems that occur by the expression of this strength and the distribution of the reinforcement. The number of the main re-bars. and the direction of laying the concrete were applied as the principal variables of the experiment. Upon experiment, there were no differences in the bond strength based on the location of the main re-bar, and a 2 % increase in the bond strength was shown in the specimen laid in the same direction as the main re-bar in comparison to that of the specimen laid in a different direction from the main re-bar. The experiment results displayed that the composite concrete had uniform performance based on the rapid reaction speed of POSS nano complex.

• Composites Research
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• 제19권6호
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• pp.1-7
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• 2006

본 논문은 수지충전공정을 활용한 상업용 항공기의 복합재 윈도우 프레임을 개발하기 위한 선행 연구이다. 윈도우 프레임을 제작하기 위해 고려중인 2종류의 카본 섬유-triaxial overbraid 와 sleeving braider-에 대해서 VaRTM 공정을 활용한 시편을 제작하고, ASTM 시험법에 따라 물성치를 얻기 위해 물리적/기계적 성질 시험이 실시되었다. 이후 복합재 윈도우 프레임의 최소 플라이수와 무게를 얻기 위해 각각의 탄소 섬유에 대하여 유한요소해석이 수행되었다. 본 연구에서는 구조물의 안전성을 평가하기 위하여 Tsai-Wu 파손강도이론을 사용했다.

• 치위생과학회지
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• 제23권1호
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• pp.60-67
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• 2023

Background: In our study, a silver diamine fluoride (SDF) compound for the treatment of dental caries was synthesized to characterize its remineralization activity upon direct application to deciduous teeth. This study aimed to use microscopic computed tomography (microCT) and nanoindentation to evaluate whether SDF composite application could effectively arrest dental caries in five exfoliated primary molars. Methods: Carious teeth were extracted and visually examined using quantitative photofluorescence devices (Qraycam and QraypenTM). After performing microCT, the SDF composite was applied to the teeth according to the manufacturer's instructions. The researchers exchanged and precipitated the irritant saliva once daily for 1 week. The teeth were sectioned longitudinally through the centers of the mesial and distal surfaces, embedded, polished, and measured using nanoindentation. Thereafter, microCT was repeated. Statistical analyses were performed using GraphPad Prism software. Results: Following SDF composite application, a remineralized layer was observed on microCT images, and the hardness increased when measured using nanoindentation. We found that demineralized enamel presented with an increased number of irregular crystals in the deep carious lesion group compared with those in the shallow carious lesion group, resulting in a rougher surface. Conclusion: The SDF composite may be used for remineralization of early caries and cessation of advanced caries in primary molars.

• Steel and Composite Structures
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• 제44권6호
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• pp.883-898
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• 2022

A hollow-core partially-encased composite beam, named HPEC beam, is investigated in this paper. HPEC beam comprises I-beam, longitudinal reinforcement, stirrup, foam formwork, and cementitious grout. The foam formwork is located on both sides of the web, and cementitious grout is cast within the steel flange. To investigate the shear performance of HPEC beams, static loading tests of six HPEC beams and three control beams were conducted. The shear span ratio and the number of studs on the shear behavior of the HPECspecimens were studied. The failure mechanism was studied by analyzing the curves of shear force versus both deflection and strain. Based on the shear span ratio (𝜆), two typical shear failure modes were observed: shear compression failure when 1.6 ≤ 𝜆 ≤ 2; and diagonal compression failure when 𝜆 ≤ 1.15. Shear studs welded on the flange can significantly increase the shear capacity and integrity of HPEC beams. Flange welded shear studs are suggested. Based on the deformation coordination theory and superposition method, combined with the simplified modified compression field model and the Truss-arch model, Modified Deformation Coordination Truss-arch (M.D.C.T.) model was proposed. Compared with the shear capacity from YB9038-2006 and JGJ138-2016, the calculation results from M.D.C.T. model could provide reasonable predictions.

• Steel and Composite Structures
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• 제50권1호
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• pp.89-105
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• 2024

Multichannel analysis of surface waves (MASW) method has exhibited broad application prospects in the nondestructive detection of interfacial debonding in steel-concrete composite structures (SCCS). However, due to the structural diversity of SCCS and the high stealthiness of interfacial debonding defects, the feasibility of MASW method needs to be investigated in depth. In this study, synthetic parametric study on MASW nondestructive debonding detection for SCCSs is performed. The aim is to quantitatively analyze influential factors with respect to structural composition of SCCS and MASW measurement mode. First, stress wave composition and propagation process in SCCS are studied utilizing 2D numerical simulation. For structural composition in SCCS, the thickness variation of steel plate, concrete core, and debonding defects are discussed. To determine the most appropriate sensor arrangement for MASW measurement, the effects of spacing and number of observation points, along with distances between excitation points, nearest boundary, as well as the first observation point, are analyzed individually. The influence of signal type and frequency of transient excitation on dispersion figures from forwarding analysis is studied to determine the most suitable excitation signal. The findings from this study can provide important theoretical guidance for MASW-based interfacial debonding detection for SCCS. Furthermore, they can be instrumental in optimizing both the sensor layout design and signal choice for experimental validation.

• 한국구조물진단유지관리공학회 논문집
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• 제11권5호
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• pp.123-134
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• 2007

본 논문은 기존 강합성 교량의 내하력 향상을 목적으로 외부 긴장재의 초기 긴장력 결정 방법을 제시하였다, 외부 긴장력은 콘크리트 슬래브 재시공 전과 후에 각각 적용하였다. 활하중에 의하여 발생하는 증가 프리스트레스력을 고려한 내하율식을 제안하여 긴장재 개수와 초기 긴장력의 결정 과정을 제시하였다. 기존 강합성 교량의 내하율 향상에 적용하여 그 타당성을 입증하였다.

• 대한소아치과학회지
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• 제29권2호
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• pp.217-225
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• 2002

시술시간을 줄이는데 유리한 재료인 유동성 복합레진을 유구치부에 사용하려고 고려할 때 중요한 물성 중 하나는 마모저항성이다. 이 연구의 목적은 유동성 복합레진의 마모저항성을 일반복합레진의 마모저항성과 비교하는 것이다. 실험에 사용된 유동성 복합레진으로 1군에서는 Arabesk flow (VOCO, Germany) 2군에서는 Tetric flow (Vivadent, Liechtenstein) 3군에서는 Aeliteflow (Bisco, U.S.A.), 4군에서는 Filtek flow (3M Dental Co, U.S.A)을 사용하였으며 대조군으로 사용한 5군의 복합레진은 Z100 (3M Dental Co, U.S.A)이었다. 시편들(n=10)은 두께 2mm, 지름 5mm의 원통모양으로 제작하여 마모시험 전 $37^{\circ}C$의 증류수에서 7일 동안 담가 놓았다. 제1소구치와 레진시편을 MTS 시스템에서 2Hz로 50,000회 접촉, 마모시켰다. 마모시험시 lateral excursion은 0.4mm, 교합력은 2-100N의 조건이었다. 마모시험후 마모된 부피, 최대마모깊이, 재료자체의 표면경도를 측정하였고 마모 되지 않은 표면과 마모가 일어난 표면을 주사전자현미경으로 관찰하였으며 다음과 같은 결과를 얻었다. 1. 마모된 부피는 3군에서 가장 적었고 4군에서 가장 많았으며 3군<1군<2군<5군<4군의 순서로 증가하였다. 2. 3군, 1군, 2군은 5군이나 4군에 비해 통계적으로 유의하게 마모부피가 적었다(p<0.05). 그러나, 3군, 1군, 2군 사이에서와 5군, 4군 사이에서는 각각 통계적으로 유의한 차이가 없었다. 3. 최대마모깊이는 1군에서 가장 낮았고, 4군에서 가장 깊었으며 1군<3군<5군<2군<4군의 순서로 증가 하였다. 4. 5군의 표면경도는 다른 유동성 복합레진군에 비해 통계적으로 유의하게 높았으나(p<0.05), 마모부피나 최대마모깊이와는 통계적으로 유의한 상관관계를 보이지 않았다. 5. 마모되지 않은 표면과 마모가 일어난 표면을 주사전자현미경으로 관찰한 결과, 유동성 복합레진군과 5군 사이에 마모양상이 다르게 나타나는 것을 볼 수 있었다.

• 대한기계학회논문집A
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• 제37권2호
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• pp.265-270
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• 2013

본 논문에서는 Tsai-Wu 파손이론을 적용하여 복합재료 자전거 프레임의 경량화를 위한 강도설계에 대하여 연구하였다. 설계에 있어서 자전거 프레임의 경량화는 중요한 문제이며, 동시에 요구 강도를 만족시켜야 한다. 하중조건으로 유럽표준위원회의 EN14764 규격에 의거하여 페달, 수직, 레벨 하중조건을 적용하였다. 복합재료는 이방성을 가지므로 적절한 적층수 및 적층 순서를 결정하는 것이 중요하다. 따라서 $[0]_{8n}$, $[90]_{8n}$, $[0/90]_{2ns}$, $[{\pm}45]_{2ns}$, $[0/{\pm}45/90]_{ns}$ 의 적층에 대하여 적층수를 변화시켜가며(n=1,2,3,4) 연구를 수행하였다. 연구 결과로부터 하중 조건에 따른 자전거 프레임의 취약부와 취약적층을 확인하였고, $[0/{\pm}45/90]_{3s}$ 이 가장 적절한 적층각 모델임을 제안하였다.