• 공업화학
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• 제10권5호
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• pp.789-795
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• 1999

본 연구에서는 비원형의 단-탄소섬유를 이용하여 시멘트 복합재를 제조하고 이 복합재의 특성(건조 수축, 동결 융해저항성, 파괴 인성)을 원형 탄소섬유보강 복합재와 비교하여 연구하였다. 그 결과 섬유의 형상과 길이에 크게 의존하였다. C형 탄소섬유보강 시멘트 복합재의 건조수축저감 효과가 다른 형상의 섬유보강 복합재에 비해 우수하였다. 이 효과는 섬유의 종횡비가 클수록 증가하였다. 또한, 동결융해 저항성은 섬유형상의 영향은 두드러지지 않았으나 섬유길이와 섬유함유율에 따라 증가하였다. 특히, C형 보강 시멘트 복합재의 파괴 인성 및 균열 저항성은 다른 것에 비해 크게 개선되었다. 이는 더 큰 계면으로 파괴에너지를 더 많이 흡수하였기 때문으로 생각된다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.212-215
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• 2002

Interfacial evaluation and damage sensing of the carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composites were performed using micromechanical test and electrical resistance measurement. As AT-PEI content increased, the fracture toughness of epoxy-AT-PEI matrix increased, and thus their interfacial shear strength (IFSS) was improved due to the improved toughness. After curing process, the changes in electrical resistance (ΔR) with increasing AT-PEI contents increased gradually because of the changes in thermal expansion coefficient (TEC) and thermal shrinkage of matrix. Matrix fracture toughness was correlated to the IFSS, residual stress and electrical resistance. The results obtained from the electrical resistance measurement during curing process, reversible stress/strain, and durability test were consistent with modified matrix toughness properties.

• 한국세라믹학회지
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• 제30권2호
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• pp.85-92
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• 1993

Oxynitride glasses in Na-Ca-Si-O-N system were prepared by melting at 135$0^{\circ}C$ for 2 hours in N2 gas. The effects of Si/Na mole ratio and the various Si3N4 contents were investigated. Stable oxynitride glasses can be obtained up to 9wt.% Si3N4 content in case the Si/Na mole ratio was 2.12 and 1.62, but $\beta$-Si3N4 was precipitated at 9wt.% Si3N4 content in case the Si/Na mole rtio was 1.12. Density (p), chemical durability, hardness (Hv), and fracture toughness (KIC) increased with increasing Si3N4 content. In cae the Si/Na mole ratio was 1.12, the increment of properties was remarkable but hardness and fracture toughness did not increase no longer owing to precipitation of $\beta$-Si3N4.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 가을 학술발표회 논문집
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• pp.145-150
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• 1990

In order to discuss the freeze-thaw durability of FRC and mechanical properties by the fiber types of FRC, experimental studies of FRC were carried out. The kinds of fiber used which are in CFRC are PAN-based and Pitch-based carbon fiber and in GFRC are alkali-resistance glass fiber. To examine the effects of the kinds, types (continuous fiber and Tow, Belt, Cloth) and contents of fiber and matrices, the following three methods CFRC and GFRC, Air cured, Water cured and Autoclaved CFRC and GFRC were tested. According to the test results, the flexural, tensile strength and toughness of FRC were remarkably influenced by types of fiber and addition of condensed silica fume. Also, freeze-thaw resistance of FRC was considerably improved in comparision to conventional mortar.

• 한국주조공학회지
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• 제14권6호
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• pp.541-547
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• 1994

The effects of weld repair on the durability in Al-10%Si-0.3%Mg castings were evaluated. The strength and fracture toughness in fusion zone were higher than those in the base metal by rapid cooling of fusion zone after welding. There were no significant differences between fatigue properties in castings and weld repaired specimen as the results of low cycle fatigue and rotating bending fatigue test. Therefore it was concluded that weld repairing did not have any significant effect on the mechanical properties of castings.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.93-105
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• 2022

The brittleness of concrete can be overcome by fiber reinforcement that controls the crack mechanisms of concrete. Corrosion-related durability issues can be prevented by synthetic fibers (SFs), while macro synthetic fibers have proven to be particularly effective to provide ductility and toughness after cracks. This experimental study has been performed to investigate the comparative flexural and mechanical behavior of four different macro-synthetic fiber-reinforced concretes (SFRCs). Two polyamide fibers (SF1 and SF2) with different aspect ratios and two different polypropylene fiber types (SF3 and SF4) were used in production of SFRCs. Four different SFRCs and reference concrete were compared for their influences on the toughness, compressive strength, elastic modulus, flexural strength, residual strength and splitting tensile strength. The outcomes of the study reveal that the flowability of reference mixture decreases after addition of SFs and the air voids of all SFRC mixtures increased with the addition of macro-synthetic fibers except SFRC2 mixture whose air content is the same as the reference mixture. The results also revealed that with the inclusion of SFs, 11.34% reduction in the cube compressive strength was noted for SFRC4 based on that of reference specimens and both reference concrete and SFRC exhibited nearly similar cylindrical compressive strength. Results illustrated that SFRC1 and SFRC4 mixtures consistently provide the highest and lowest flexural toughness values of 36.4 joule and 27.7 joule respectively. The toughness values of SFRC3 and SFRC4 are very near to each other.

• Advances in concrete construction
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• 제15권3호
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• pp.161-170
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• 2023

Ultra-high-performance concrete (UHPC) is produced using high amount of cementitious materials, very low water/cementitious materials ratio, fine-sized fillers, and steel fibers. Due to the dense microstructure of UHPC, it possesses very high strength, elasticity, and durability. Besides that, the UHPC exhibits high ductility and fracture toughness due to presence of fibers in its matrix. While the high ductility of UHPC allows it to undergo high strain/deflection before failure, the high fracture toughness of UHPC greatly enhances its capacity to absorb impact energy without allowing the formation of severe cracking or penetration by the impactor. These advantages with UHPC make it a suitable material for construction of the structural members subjected to special loading conditions. In this research work, the UHPC mixtures having three different dosages of steel fibers (2%, 4% and 6% by weight corresponding to 0.67%, 1.33% and 2% by volume) were characterized in terms of their mechanical properties including facture toughness, before using these concrete mixtures for casting the slab specimens, which were tested under high-energy impact loading with the help of a drop-weight impact test setup. The effect of fiber content on the impact energy absorption capacity and central deflection of the slab specimens were investigated and the equations correlating fiber content with the energy absorption capacity and central deflection were obtained with high degrees of fit. Finite element modeling (FEM) was performed to simulate the behavior of the slabs under impact loading. The FEM results were found to be in good agreement with their corresponding experimentally generated results.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2007년도 추계 학술논문 발표대회
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• pp.71-74
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• 2007

With the changes of times the building materials tend to extend the demand for application under the special environment. Since high-ductile mortar is developed, the building materials show excellent performance like toughness, compression, tensile, and bending, etc. in the general concrete from the existing brittle point. And, recently they are widely used as repairing and reinforcing materials both at home and abroad because they are recognized as excellence like durability and fire-resistance. However, it is in a situation of creating problems in durability because it frequently happened deterioration of buildings that have already repaired and reinforced at a time when it requires reconstruction of recently deteriorated construction structure recently. Therefore, in this study improved with a more repair Material development and reinforcement of the second high-ductile mortar products for a variety of basic materials were presented want, research plans used include traditional repair materials and the newly developed PCM (polymer cement mortar) structural reinforcement type indicated that comparison. PCM analysis in order to present a rate depending on the types fiber 0, 1.2 and 2.0(%) at three levels and mixture water according to ratios of weight to Plain in the 2.0 and 1.85(kg) at two levels is set, the results were as follows. 1) This study has shown that PCM had excellent strain hardening behavior at the same time that the bending stress increased according to the fiber contents. 2) This study has shown that it had the durability performance due to the high substance transmission according to the fiber contents.

• 콘크리트학회논문집
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• 제15권1호
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• pp.110-116
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• 2003

근년, 콘크리트구조물이 고층화, 대형화됨에 따라 고강도, 고유동, 고내구성인 고성능 콘크리트의 수요가 많아지고 있다. 이러한 고성능 콘크리트는 보통콘크리트에 비하여 압축강도가 크고, 시공성 및 내구성이 우수한 것이 장점이지만, 보통강도 콘크리트에 비하여 파괴형태가 취성적인 것이 단점으로 제시되고 있다. 따라서, 본 연구는 W/B 30% 및 40%에서 메탈라스, 유리섬유 및 탄소섬유로 횡구속된 고성능 콘크리트의 역학적 특성을 분석하여 압축강도 및 인성개량방법을 제안하고자 하였다. 연구결과 압축강도는 횡구속재의 횡구속력의 증대에 기인하여 메탈라스, 탄소섬유 및 유리섬유의 순으로 증가하였다. 또한, 횡구속재 변화에 따른 응력-변형도곡선에서 플레인의 경우는 최대하중 이후 취성파괴로 나타난 반면, 횡구속된 경우로, 특히 메탈라스로 횡구속하였을 때에는 인성증가로 변형율이 증가하여 어느 정도 취성이 개량됨을 알 수 있었다. 탄성계수는 보강하지 않은 콘크리트와 비교하여 약간 큰 값으로 압축강도의 경향과 비슷한 양상이었다.

• 대한심미치과학회지
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• 제23권2호
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• pp.86-94
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• 2014

In recent years, perhaps the biggest driver in new material development is the desire to improve crown and bridge esthetics compared to the traditional PFM or all-metal restorations. As such, zirconia, leucite-containing glass ceramic and lithium disilicate glass ceramic have become prominent in the dental practice. Each material type performs differently regarding strength, toughness, ease of machining and the final preparation of the material prior to placement. For example, glass ceramic are typically weaker materials which limits its use to single-unit restorations. On the other hand, zirconia has a high fracture toughness which enables multi-unit restorations. This material requires a long sintering procedure which excludes its use for fast chair side production. Developed hybrid material of CAD/CAM is contained nano ceramic elements. This new material, called a Resin Nano Ceramic is unique in durability and function. The material is not a resin or composite. It is also not a pure ceramic. The material is a mixture of both and consists of ceramic. Like a composite, the material is not brittle and is fracture resistant. Like a glass ceramic, the material has excellent polish retention for lasting esthetics. The material is easily machined chair side or in a dental lab, polishes quickly to an esthetic finish and if necessary, can be useful restoratives.