• 한국지반환경공학회 논문집
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• 제9권5호
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• pp.29-36
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• 2008

숏크리트는 NATM공법에서 터널 굴착 후 지반안정을 위한 주요 지보재로서 시공기간의 단축과 시공비용 절감을 위해 일반콘크리트 라이닝을 대신하여 영구 숏크리트 라이닝의 사용이 요구되고 있는 추세이다. 이러한 영구 숏크리트 라이닝으로 사용하기 위해 고성능고강도 숏크리트가 요구되고 있으며, 인체에 대한 유해성 및 환경오염의 감소방안도 해결해야 할 문제로 부각되고 있다. 따라서, 본 연구에서는 NATM공법 시공시 조기에 고강도 발현이 가능한 숏크리트재료를 개발하기 위하여 시멘트광물계 급결재를 사용하여 강도측정용 공시체를 제작하여 기존에 쓰여지고 있는 숏크리트재료와 비교하여 일축압축시험, 휨강도시험, 수중불분리시험을 실시하였고, 환경영향성을 평가하기 위해 어독성시험을 실시하였다. 시험결과, 일축압축강도 및 휨강도는 연구대상재료의 재령 7일강도가 기존재료의 28일 강도와 대등하였으며, 수중불분리시험 결과 연구대상재료의 불분리성이 우수하게 나타났다. 환경영향성(어독성시험)평가 결과 기존숏크리트에 비해 연구대상재료가 친환경적인 것으로 나타났다.

• Journal of the Korean Wood Science and Technology
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• 제47권5호
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• pp.655-662
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• 2019

This study evaluated the multi-bonding performances of timbers as well as those of reinforcement and timber to obtain data for preparing guidelines regarding the use of timbers as large structural members. For the multi-bonding performances of timbers, four types of bonding surfaces were prepared according to the pith position. For the bonding performances of FRP (fiber-reinforced plastic)/steel plate and timber, a total of 11 types of specimens were produced for the selection of the appropriate adhesive. The bonding performances of the produced specimens were evaluated through a water soaking delamination test, a water boiling delamination test, and a block shear strength test. The test results showed that the bonding strength of the bonding surface according to the pith position was highest in the specimen for which the two sections with the pith at the center of the cross-section on timber and between the bonding surfaces (the tangential and radial sections were mixed) were bonded. Furthermore, the specimens for which the section (radial section) with the pith on the bonding surface of the timber was bonded showed a high delamination percentage. The results of the block shear strength test showed that the bonding section did not have a significant effect on the shear strength, and that the measured wood failure percentage was higher than the KS standard value. The PVAc adhesive showed the highest bonding strength between larix timber and GFRP (glass FRP). Furthermore, the epoxy and polyurethane adhesives showed good bonding strength for CFRP (carbon FRP) and structure steel, respectively.

• 한국안전학회지
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• 제33권6호
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• pp.15-21
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• 2018

Ships may collide with reefs or other objects during operation, when arriving or departing ports. The hull plate may be damaged due to the contact with other ships. The total number of domestic powered fishing vessels has decreased, but that of FRP fishing vessels has increased by 0.7% and the ratio of FRP fishing vessels to the total fishing vessels increased to 96%. Recently, fishing vessels has been used as fishing boats for income of non-fishermen as well as fishermen. Therefore, safety management for repair and maintenance is necessary. The penetration of moisture and moisture in the composite material such as FRP may deteriorate the mechanical properties and the salt (NaCl) component of the damaged portion may cause a relatively high deterioration in material strength. The gel coat painting is the final stage of repairs ans maintenance of FRP fishing vessels. The thickness criteria in the domestic and foreign gel coat is 0.3~0.762 mm. The joint specimens, which was immersed in seawater for 120 days, were compared with those without seawater immersion. As a result, the tensile strength was 83 ~ 121.8% and the flexural strength was 83 ~ 113% compared with the specimens without seawater immersion. According to the previous study the tensile strength decreased by more than 29% and the flexural strength decreased by more than 50% when the composite material was immersed in seawater for 1,083 hours without coating. As a result, it was found that the gel coat with 0.5 mm thickness is very effective in preventing the strength decrease of the composite material.

• Computers and Concrete
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• 제30권6호
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• pp.393-407
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• 2022

Due to the enormous cement content, pozzolanic materials, and the use of different aggregates, sustainable controlled low-strength material (CLSM) has a higher material cost than conventional concrete and sustainable construction issues. However, by selecting appropriate materials and formulations, as well as cement and aggregate content, whitethorn costs can be reduced while having a positive environmental impact. This research explores the desire to optimize plastic properties and 28-day unconfined compressive strength (UCS) of CLSM containing powder content from unprocessed-fly ash (u-FA) and recycled fine aggregate (RFA). The mixtures' input parameters consist of water-to-cementitious material ratio (W/CM), fly ash-to-cementitious materials (FA/CM), and paste volume percentage (PV%), while flowability, bleeding, segregation index, and 28-day UCS were the desired responses. The central composite design (CCD) notion was used to produce twenty CLSM mixes and was experimentally validated using MATLAB by an Artificial Neural Network (ANN). Variance analysis (ANOVA) was used for the determination of statistical models. Results revealed that the plastic properties of CLSM improve with the FA/CM rise when the strength declines for 28 days-with an increase in FA/CM, the diameter of the flowability and bleeding decreased. Meanwhile, the u-FA's rise strengthens the CLSM's segregation resistance and raises its strength over 28 days. Using calcareous powder as a substitute for cement has a detrimental effect on bleeding, and 28-day UCS increases segregation resistance. The response surface method (RSM) can establish high correlations between responses and the constituent materials of sustainable CLSM, and the optimal values of variables can be measured to achieve the desired response properties.

• 한국염색가공학회지
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• 제34권4호
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• pp.241-249
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• 2022

As for military backpacks in Korea, utility backpack products equipped with various functions along with comfort and convenience are being developed. As a result, the volume and weight of the backpack increase, and many lightweight studies of the materials forming the backpack are being conducted. This study is a basic study on frame lightweight using fiber-reinforced composites to deal with aluminum, a back frame that maintains the shape of a backpack and provides stability when worn by combatants. As is known, only fiber-reinforced composites have sufficient light weight and mechanical properties, but the mechanical properties were reviewed by drilling holes to maximize the light weight. Tensile strength and flexural strength were measured by drilling 6mm, 12mm, 18mm, and 24mm holes, and the tensile strength and flexural strength were measured when 1, 3, 5, and 7 holes of 12mm were increased. As a result, even when the number of holes was increased, tensile strength did not change significantly, and the flexural strength showed to be higher in the case of 3 holes and 5 holes than in the case of 1 hole.

• The Journal of Advanced Prosthodontics
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• 제14권4호
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• pp.262-272
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• 2022

PURPOSE. This study aimed to analyze the shear bond strength between the 3D-printed denture base and the chairside relining material, according to the surface treatment. MATERIALS AND METHODS. Cylindrical specimens were prepared using DENTCA Denture Base II. The experimental groups were divided into 6 (n = 10): no surface treatment (C), Tokuyama Rebase II Normal adhesive (A), sandblasting (P), sandblasting and adhesive (PA), sandblasting and silane (PS), and the Rocatec system (PPS). After bonding the chairside relining material to the center of the specimens in a cylindrical shape, they were stored in distilled water for 24 hours. Shear bond strength was measured using a universal testing machine, and failure mode was analyzed with a scanning electron microscope. Shear bond strength values were analyzed using one-way analysis of variance, and Tukey's honest significant difference test was used for post-hoc analysis (P < .05). RESULTS. Group PPS exhibited significantly higher shear bond strength than all other groups. Groups P and PA displayed significantly higher bond strengths than the control group. There were no significant differences between groups PS and A compared to the control group. Regarding the failure mode, adhesive failure occurred primarily in groups C and A, and mixed failure mainly in groups P, PA, PS, and PPS. CONCLUSION. The shear bond strength between the 3D-printed denture base and the chairside relining material exhibited significant differences according to the surface treatment methods. It is believed that excellent adhesive strength will be obtained when the Rocatec system is applied to 3D-printed dentures in clinical practice.

• 한국지반공학회논문집
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• 제22권10호
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• pp.33-45
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• 2006

C.S.G(Cemented Sand and Gravel) 재료는 댐 수몰지로부터 쉽게 얻을 수 있는 굴착토와 하상자갈에 소량의 시멘트와 물을 혼합한 재료를 총칭하는 것으로 최근 댐, 도로, 호안등의 건설재료로 그 활용성이 점차 증가하고 있다. 통상적으로 C.S.G 재료의 강도특성은 입도분포, 단위시멘트량, 재령, 그리고 함수비 등과 같은 여러 가지 요소에 의하여 영향을 받는 것으로 보고되고 있다. 본 연구에서는 화북댐 유역의 하상자갈을 3가지 종류의 입도분포로 재구성하여 재령, 단위시멘트량 그리고 함수비의 혼합 비율에 따른 일축압축강도의 변화를 연구하였다. 실험결과 C.S.G 재료의 일축압축강도는 상기 영향 인자들에 의하여 다양하게 영향을 받았으며, 특히 입도분포와 단위수량은 C.S.G 재료의 강도를 결정하는데 매우 중요한 인자임을 알 수 있었다. 또한 이러한 실험적 결과를 토대로 각 영향인자를 고려한 강도 예측식을 제안함으로써 설계 및 시공에 필요한 기초적인 자료를 제공하고자 한다.

• 한국구조물진단유지관리공학회 논문집
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• 제11권2호
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• pp.77-84
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• 2007

본 연구에서는 이방성 재료로 구성된 파형 관로의 좌굴 거동을 분석하였으며, 좌굴거동에 영향을 미치는 변수로서 파형의 높이와 길이, 암거의 직경과 두께가 고려되었다. 또한 이방성 재료의 특성을 고려하여, 길이방향의 강성과 원주방향의 강성도 함께 좌굴거동에 영향을 미치는 인자로서 고려되었다. 다양한 형상의 파형 관로에 대해 유한요소해석을 수행하여 매개변수연구를 하였으며, 유한요소해석 결과를 바탕으로 이방성 재료로 구성된 파형 관로의 좌굴강도를 추정할 수 있는 간략식을 제안하였다. 해석결과, 파형 관로는 일반적인 평탄한 관로에 비해 우수한 좌굴강도를 보였으며, 제안식 또한 유한요소해석 결과에 근접하는 좌굴강도를 보여주었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.250-253
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• 2000

The fiber orientation in FRP has a great effect on the strength of FRP because the strength of FRP mainly depends on the strength of fiber. Unidirectional FRP made by pultrusion method has comparatively lower compressive strength than tensile strength. Compressive strength of unidirectional FRP may be increased by filament winding layer which has tensile stress when compressive stress was loaded. In this study, compressive strength and stresses of FRP rods were simulated according to the winding orientation of glass fiber. Inner part of FRP was made unidirectionally by pultrusion method and outer part of FRP was made by filament winding method. Simulated value and real evaluated compressive strength were compared to investigate stresses which is prominent to the fracture of FRP. The shear stresses had a great effect on the strength of FRP although the stress of parallel direction of FRP was much higher.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.436-439
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• 2003

FRP has been used widely for insulator. FRP consists of fiber and resin. The fiber contributes the high strength and modulus to the composite. The fiber orientation in FRP has a great effect on the strength of FRP because the strength of FRP mainly depends on the strength of fiber. In this study, FRP was made unidirectionally by pultrusion method. Outer part of the FRP was made by filament winding method to give fiber orientation to the FRP. And outer part of FRP was also made by wrapping method. The bending strength and bending stresses of FRP rods were simulated according to the winding orientation of glass fiber. The bending strength of FRP was also evaluated. The results of simulation and evaluation were compared each other to investigate main stresses which affect the fracture of FRP. The main stresses which had a great effect on the strength of FRP were shear stresses. Bending strength of the FRP was different with the winding angle. The bending strength of $15^{\circ}$ winded FRP was the highest.