• Computers and Concrete
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• 제8권3호
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• pp.357-369
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• 2011

In this study, effect of steel fibers on toughness and some mechanical properties of concrete were investigated. Hooked-end steel fibers were used in concrete samples with three volume fractions (${\nu}_f$) of 0.5%, 0.75% and 1% and for two aspect ratios (l/d) of 45 and 65. Compressive and flexural tensile strength and modulus of elasticity of concrete were determined for cylindrical, cubic and prismatic samples at the age of 7 and 28 days. The stress-strain curves of standard cylindrical specimens were studied to determine the effect of steel fibers on toughness of steel-fiber-reinforced concrete (SFRC). In addition, the relationship between compressive strength and the flexural tensile strength of SFRC were reported. Finally, a simple model was proposed to generate the stress-strain curves for SFRC based on strains corresponding to the peak compressive strength and 60% of peak compressive stress. The proposed model was shown to provide results in good correlation with the experimental results.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.458-466
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• 2020

이 연구의 목적은 비정질 강섬유와 폴리아미드 섬유를 이용한 고성능 하이브리드 섬유보강 콘크리트의 압축 및 인장 거동을 평가하는 것이다. 이를 위하여 목표 압축강도 40MPa 및 60MPa 각각에 대해서 비정질 강섬유와 폴리아미드 섬유를 총 부피비로 1.0% 혼입한 고성능 하이브리드 섬유보강 콘크리트를 제작한 후 압축강도, 압축인성, 직접인장강도 및 응력-변형률 특징 등의 압축 및 인장 거동을 평가하였다. 그 결과, 고성능 하이브리드 섬유보강 콘크리트의 압축강도는 플레인 콘크리크보다 다소 감소하였으나, 압축인성, 압축인성 비, 직접인장강도는 크게 증가하는 것으로 나타났다. 또한 압축 및 인장 시험시 플레인 콘크리트는 최대응력 이후 취성파괴를 나타냈으나, HPHFRC는 변형연화 현상을 나타내어, 압축 및 인장 거동이 크게 개선되는 것으로 나타났다.

• Composites Research
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• 제14권3호
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• pp.51-56
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• 2001

섬유강화 고분자기지 복합재에 있어 탄성계수, 최대응력, 최대변형률, 파괴특성 등이 압력에 의해 영향을 받는다는 것은 잘 알려진 사실이다. 본 연구에서는 준등방성이며 두꺼운 두께를 갖는 [0$^{\circ}$/$\pm$45$^{\circ}$/90$^{\circ}$]$_{11s}$ 로 적층된 탄소섬유/에폭시 복합재에 있어 압력을 0.1 MPa, 100 MPa, 200 MPa, 300 MPa로 변화시켜 압축 파괴실험을 수행하였으며 이로부터 압력변화에 따른 파괴특성 변화에 대해 검토하였다. 결과로서 가해진 압력이 증가함에 따라 압축파괴인성은 증가함을 알수 있었다. 구체적으로 압력이 대기압에서 300 MPa으로 증가할 때 압축파괴인성 값은 약 44% 증가하였다.

• Advances in concrete construction
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• 제13권 2호
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• pp.123-132
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• 2022

This paper aims to adapt Multilinear regression (MLR) to predict the strength and toughness of SIFCON containing various pozzolanic materials. Slurry Infiltrated Fibrous Concrete (SIFCON) is one of the most common terms used in concrete manufacturing, known for its benefits such as high ductility, toughness and high ultimate strength. Assessment of compressive strength (CS.), flexural strength (F.S.), splitting tensile strength (STS), dynamic elasticity modulus (DME) and impact energy (I.E.) using the experimental approach is too costly. It is time-consuming, and a slight error can lead to a repeat of the test and, to solve this, alternative methods are used to predict the strength and toughness properties of SIFCON. In the present study, the experimentally investigated SIFCON data about various mix proportions are used to predict the strength and toughness properties using regression analysis-multilinear regression (MLR) models. The input parameters used in regression models are cement, fibre, fly ash, Metakaolin, fine aggregate, blast furnace slag, bottom ash, water-cement ratio, and the strength and toughness properties of SIFCON at 28 days is the output parameter. The models are developed and validated using data obtained from the experimental investigation. The investigations were done on 36 SIFCON mixes, and specimens were cast and tested after 28 days of curing. The MLR model yields correlation between predicted and actual values of the compressive strength (C.S.), flexural strength, splitting tensile strength, dynamic modulus of elasticity and impact energy. R-squared values for the relationship between observed and predicted compressive strength are 0.9548, flexural strength 0.9058, split tensile strength 0.9047, dynamic modulus of elasticity 0.8611 for impact energy 0.8366. This examination shows that the MLR model can predict the strength and toughness properties of SIFCON.

• 한국구조물진단유지관리공학회 논문집
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• 제23권3호
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• pp.43-50
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• 2019

본 연구는 강섬유의 인장강도 및 형상비가 고강도 및 보통강도 강섬유보강 콘크리트(Steel fiber-reinforced concrete, SFRC)의 압축 및 휨 거동에 미치는 영향을 평가하기 위하여 실시되었다. 또한 본 연구에서는 가력속도에 따른 SFRC의 압축거동을 평가하였다. 이를 위해 총 4종류의 강섬유가 설계기준 압축강도 35 및 60 MPa급 SFRC에 각각 사용되었다. 압축거동 평가를 위해 지름 150 mm 및 높이 300 mm의 원주형 공시체를 사용하였으며, 단면 $150{\times}150mm$ 및 지간 450 mm의 각주형 공시체를 사용하여 휨 거동 평가를 실시하였다. 실험결과 강섬유의 혼입은 콘크리트의 인성을 크게 향상시키는 것으로 나타났으며, 고강도 강섬유의 사용은 고강도 SFRC의 성능개선에 효과적인 것으로 나타났다. 아울러 본 연구에서는 SFRC의 휨 인성지수에 근거한 압축인성지수 산정기법을 제안하였다.

• 대한기계학회논문집A
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• 제24권12호
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• pp.3010-3017
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• 2000

For integrity evaluation of cracked or damaged structures, fracture toughness test results in ASTM are widely used. The fracture toughness values of the structures are used as an effective design criterion in nuclear plants and aircraft structures. Sometimes the difference of P-$\delta$ curve trend during the unloading /reloading cycle in the fracture toughness test using partial unloading compliance was observed. The phenomenon as a possible source of error in determining fracture toughness may be caused by the residual stress during unloading work-hardening and bucking of a specimen. Therefore, we evaluate the effect of bucking and compressive residual stress during the K-R and J-R testing using a finite element method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.314-319
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• 2004

High temperature fracture toughness characteristics of shot peened spring steel(SUP-9), which is used for automobile suspension system and railroad, was investigated in this paper. Fracture tougness test for room temperature, $100^{\circ}C$ , and $200^{\circ}C$ were evaluated by material test system(MTS). The experimental results show that the fracture toughness was improved by peened and unpeened. The fracture toughness for high temperature were also improved by peened and unpeened.

• 한국건축시공학회지
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• 제15권3호
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• pp.351-357
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• 2015

Fiber reinforced concrete (FRC) has been successfully used to enhance the flexural toughness of concrete. As fibers are randomly oriented in FRC, they sometimes produce clumps that reduce the mechanical performance, and a properly chosen mixing protocol can be a way to minimize this problem. In this research, the effects of mixing method on the mechanical properties of FRC were investigated. The compressive strength, flexural strength, and flexural toughness were measured using three different mixing methods. It was shown from the results that the compressive strength and peak flexural load were not affected by changes in mixing method. However, in terms of flexural toughness, the changes in mixing method clearly affected the flexural toughness of FRC. The truck-mixed FRC outperformed two pan-mixed FRCs.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.359-364
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• 1998

The interfacial zone in concrete materials is extensive, geometrically complex, and constitutes inherently weak zones that limit the concrete performance. Motar-aggregate interfaces play a major role in the fracture processing in concrete composites. Also, the interfacial bond considerably influence mechanical properties of concrete such as modulus of elasticity, strength, and fracture energy, Characterization of the interfacial properties is, therefore, essential to overcome the limitations associated with the interfaces. an objective of this paper is to investigate the corelationship between the fracture toughness of mortar-aggregate interface and the concrete properties such as strengths and elastic moduli. It is observed from the test results that interface fracture toughness is closely related with the compressive strength rather than other properties. At early ages, the development of both tensile strength and elastic modulus are much greater thatn that of both interface fracture toughness and compressive strength.

• Fibers and Polymers
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• 제5권3호
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• pp.187-197
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• 2004

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.