• Structural Engineering and Mechanics
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• 제65권2호
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• pp.163-171
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• 2018

Plain concrete is a brittle material with a very low tensile strength compared to compressive strength and critical tensile strain. This study analyzed the dynamic characteristics of high-performance fiber-reinforced cementitious composites based on slurry-infiltrated fiber concrete (SIFCON-based HPFRCC), which maximizes the steel-fiber volume fraction and uses high-strength mortar to increase resistance to loads, such as explosion and impact, with a very short acting time. For major experimental variables, three levels of fiber aspect ratio and five levels of fiber volume fraction between 6.0% and 8.0% were considered, and the flexural strength and toughness characteristics were analyzed according to these variables. Furthermore, three levels of the aspect ratio of used steel fibers were considered. The highest flexural strength of 65.0 MPa was shown at the fiber aspect ratio of 80 and the fiber volume fraction of 7.0%, and the flexural strength and toughness increased proportionally to the fiber volume fraction. The test results according to fiber aspect ratio and fiber volume fraction revealed that after the initial crack, the load of the SIFCON-based HPFRCC continuously increased because of the high fiber volume fraction. In addition, sufficient residual strength was achieved after the maximum strength; this achievement will bring about positive effects on the brittle fracture of structures when an unexpected load, such as explosion or impact, is applied.

• 한국농공학회논문집
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• 제48권3호
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• pp.85-94
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• 2006

Practially useful method of steel fiber for construction work is presented in this study. The most important purpose of this study is to develop a model which can predict mechanical behavior of the structure according to aspect ratio and volume fraction of steel fiber. Experiments on compressive strength, elastic modulus, and splitting strength were performed with self-made cylindrical specimens of variable aspect ratios and volume fractions. The experiment showed that compressive strength was not in direct proportion to volume fraction which doesn't seem to have great influence over compressive strength. However, splitting strength showed almost direct proportion to aspect ratio and volume fraction. Improvement of optimal efficiency was confirmed when the aspect ratio was 70. Experiments on flexural strength, fracture energy, and characteristic length were carried out with self-manufactured beams with notch. As a result, increases of flexural strength, fracture energy, and characteristic length according to increase of volume fraction tend to be prominent when aspect ratio is 70. The steel fiber improves concrete to be more ductile and tough. Moreover, regression analysis was the performed and predictable model was developed after determining variables. With comparison and analysis of suggested estimated values and measured data, reliance of the model was verified.

• 대한기계학회논문집A
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• 제25권4호
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• pp.564-573
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• 2001

The mechanical properties of short carbon/glass fiber reinforced polypropylene are experimentally measured as functions of fiber content and nozzle diameter. Also, these properties are compared with the survival rate of reinforced fibers and fiber volume fraction using image analysis after pyrolytic decomposition. The survival rate of fiber aspect ratio as well as fiber volume fraction is influenced by injection processing condition, the used materials and mold conditions such as diameter of nozzle, etc. In this study, the survival rate of fiber aspect ratio is investigated by nozzle size variations in injection/mold sides. It is found that the survival rate of glass fiber is higher that the survival rate of glass fiber is higher than that of carbon fiber. Both tensile modulus and strength of short-fiber reinforced polypropylene are improved s the fiber volume fraction and nozzle diameter are increased.

• 한국농공학회논문집
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• 제57권2호
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• pp.67-73
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• 2015

This study evaluated the effects of fibers on the void ratio, compressive strength and repeated freezing and thawing resistance of porous vegetation concrete with binder type (non-sintering inorganic binder and blast furnace slag cement) and natural jute fiber volume fraction (0.0 %, 0.1 % and 0.2 %). The natural jute fiber volume fraction affected the void ratio, compressive strength and repeated freezing and thawing resistance. Added of natural jute fiber resulted in improved properties of the void ratio, compressive strength and freezing and thawing resistance. Also, the both compressive strength and freezing and thawing resistance increased with natural jute fiber volume fraction up to 0.1 % and then decreased with fiber volume fraction at 0.2 %.

• 콘크리트학회논문집
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• 제16권6호
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• pp.759-766
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• 2004

강섬유(steel fiber) 보강은 전단 강도와 같은 콘크리트 구조 부재의 많은 공학적 특성들을 현저히 향상시킨다. 본 연구는 구조 부재로의 실용적 사용을 위해 강섬유의 형상, 형상비, 혼입률, 강섬유 계수를 강도 특성 및 변형 특성의 수준으로 평가하였다. 기존 연구 및 본 연구의 재료 시험 결과들을 평가한 결과, 양단고리형 및 최대골재치수의 1.5배 이상되는 길이의 강섬유의 강도 보강효과가 우수한 것으로 판단된다. 또한 강도 및 변형 능력에 대한 상세 시험결과로부터, 형상비 75, 혼입률 $1.5\%$가 적절한 것으로 판단된다. 결론적으로 재료 성능 시험 결과들을 통계적로부터 추정한 결과, 강섬유 계수, 할렬인장강도, 휨강도가 SFRC의 주요한 특성인자로 판단된다.

• 한국농공학회논문집
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• 제52권1호
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• pp.69-77
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• 2010

Research on permeable pavement like asphalt and concrete pavement with porous structure has been increasing due to environmental and functional need such as reduction of run off and flood, and increase and purification of underwater resource. This study was performed to evaluate permeability, strengths and durability of permeable polymer concrete (PPC) using recycled aggregate that is obtained from waste concrete. Also, 6mm length of polypropylene fiber was used to increase toughness and interlocking between aggregate and aggregate surrounded by binder. In the test results, regardless of kinds of aggregates and fiber contents, the compressive strength and permeability coefficient of all types of PPC showed the higher than the criterion of porous concrete that is used in permeable pavement in Korea. Also, strengths of PPC with increase polypropylene fiber volume fraction showed slightly increased tendency due to increase binder with increase of fiber volume fraction. The weight reduction ratios for PPC after 300 cycles of freezing and thawing were in the range of 1.6~3.8 % and 2.2~5.6 %, respectively. The weight change ratio was very low regardless of the fiber volume fraction and aggregates. The weight reduction ratios of PPC with fiber and aggregate were in the range of 1.3~2.7 % and 2.2~3.2 % after 13 weeks and was very low regardless of the fiber volume fraction and aggregates.

• 대한토목학회논문집
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• 제31권2A호
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• pp.105-113
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• 2011

본 연구는 보강섬유의 종류(마섬유, 펄프섬유, PVA섬유, 나이론섬유) 및 혼입률(0.0%, 0.1%, 0.2%, 0.3%)이 다공성 식생콘크리트의 역학적 특성과 내약품성에 미치는 효과를 평가하였다. 시험은 섬유의 종류 및 혼입률의 변화에 따른 다공성 식생콘크리트의 압축강도, 공극률, pH, 휨강도 및 내약품성 특성을 분석하기 위하여 수행하였다. 섬유의 종류 및 혼입률은 다공성 식생콘크리트의 압축강도, 공극률 및 내약품성에 영향을 미쳤다. 섬유의 혼입률이 증가할수록 압축강도, 휨강도 및 공극률은 증가하였다. 그렇지만 다공성 식생콘크리트의 pH 값과 내약품성은 섬유의 종류 및 혼입률의 변화에 큰 영향이 없었다.

• 수산해양기술연구
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• 제41권1호
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• pp.78-84
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• 2005

The main goal of this work is to study the effects of temperature and volume fraction of fiber on the Charpy impact test with GF/PP composites. The critical fracture energy and failure mechanisms of GF/PP composites are investigated in the temperature range of 60^{\circ}C$ to -50^{\circ}C$ by impact test. The critical fracture energy increased as the fiber volume fraction ratio increased. The critical fracture energy shows a maximum at ambient temperature and it tends to decreases as temperature goes up or goes down. Major failure mechanisms can be classified such as fiber matrix debonding, fiber pull-out and/or delamination and matrix deformation.

• 대한기계학회논문집A
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• 제29권2호
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• pp.318-324
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• 2005

Theoretical efforts are performed to extend the formulation of NSLT(New Shear Lag Theory) for the prediction of the elastic modulus in short fiber composite. The formulation is based on the elastic stress transfer considering the stress concentration effects influenced by elastic modulus ratio between fiber and matrix. The composite modulus, thus far, is calculated by changing the fiber aspect ratio and volume fraction. It is found that the comparison with FEA(Finite Element Analysis) results gives a good agreement with the present theory (NSLT). It is also found that the NSLT is more accurate than the SLT(Shear Lag Theory) in short fiber regime when compared by FEA results. However, The modulus predicted by NSLT becomes similar values that of SLT when the fiber aspect ratio increases. Finally, It is shown that the present model has the capability to predict the composite modulus correctly in elastic regime.

• 소성∙가공
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• 제18권1호
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• pp.45-51
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• 2009

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy fiber and Al2024 sheets were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 shape memory alloy composite was made by using hot press method. In order to investigate bonding condition between TiNi reinforcement and Al matrix, the micro-structure of interface was observed by using optical microscope and diffusion layer of interface was measured by using Electron Probe Micro Analyser. And the mechanical properties of composite with three parameters(volume fraction of fiber, cold rolling amount and test temperature) were obtained by tensile test. The most optimum bonding condition for fabrication the TiNi/Al2024 composite material was obtained as holding for 30min. under the pressure of 60MPa at 793K. The strength of composite material increased considerably with the volume fraction of fiber up to 7.0%. And the tensile strength of this composite increased with the reduction ratio and it also depends on the volume fraction of fiber.