• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.759-766
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• 2004

The addition of steel fiber with concrete significantly improves the engineering properties of structural members, notably shear strength. The purpose of this study is to determine the steel fiber shape, aspect ratio and volume fraction ratio in a point of practical usage as structural members. Steel fiber factor and volume fraction are also considered to verify the strengthening effect in member level. From the reviewing of previous researches and analyzing of consecutive material test results, the optimum shape and length of steel fiber, which can have a good strengthening effects were defined as a hooked end type and larger than 1.5 times of maximum gravel size. Analyzing the test results of strength and deformation capacity, aspect ratio 75 and volume fraction $1.5\%$ can be having a maximum strengthening effect of steel fiber. Also steel fiber factor, tensile splitting strength, and flexural strength are found as key parameter in shear strengthening effect in member level.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.631-637
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• 2007

This study was to evaluate bond properties between high-strength steel fiber reinforced concrete and high strength steel rebar. An direct bond test were performed to evaluate the bond performance of high strength steel rebar in two types of high-strength concrete with steel fiber volume fraction (0, 20, $40kg/m^3$). Also, relative bond strength was defined to determine the effect of steel fiber volume fraction on bond strength. The bond test results showed that the bond performance of high strength steel rebar and high strength concrete tended to increase with higher compressive strength and steel fiber volume fraction. Relative bond strength which performed to analyze effect of steel fiber volume fraction showed increased relative bond strength with increased steel fiber volume fraction.

• Computers and Concrete
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• v.22 no.1
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• pp.63-70
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• 2018

The steel fiber reinforced concrete (SFRC) shows better performance under dynamic loading than conventional concrete in virtue of its good ductility. In this paper, a series of quasi-static experiments were carried out on the SFRC with volume fractions from 0 to 6%. The compressive strength increases by 38% while the tension strength increases by 106% when the fraction is 6.0%. The contact explosion tests were also performed on the ${\Phi}40{\times}6cm$ circular SFRC slabs of different volume fractions with 20 g RDX charges placed on their surfaces. The volume of spalling pit decreases rapidly with the increase of steel fiber fraction with a decline of 80% when the fraction is 6%, which is same as the crack density. Based on the experimental results, the fitting formulae are given, which can be used to predict individually the change tendencies of the blast crater volume, the spalling pit volume and the crack density in slabs with the increase of the steel fiber fraction. The new formulae of the thickness of damage region are established, whose predictions agree well with our test results and others. This is of great practical significance for experimental investigations and engineering applications.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.3
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• pp.151-155
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• 1997

In this research, nondestructive test using a radioisotope, $^{241}Am$ gamma-ray, was accomplished in order to evaluate the fiber volume fraction of the accumulated composite layers such as glass fiber/epoxy and carbon fiber/epoxy. Attenuation coefficients of the fiber and resin were measured respectively by NaI(T1) detector The fibers volume fraction was measured for various thickness of composite layers between 2 and 20mm. Fiber volume fraction of the composite layers were also measured for various amount of fibers. The experimental errors from nondestructive test using gamma-ray were in the range of ${\pm}1{\sim}2.5%$ in comparison with those from observation by optical microscopy. By selecting the optimum energy and activity of radioisotope, this method can provide a new means for the evaluation of the fiber volume fraction.

• Composites Research
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• v.28 no.5
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• pp.311-315
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• 2015

Measuring fiber volume fraction properly is very important in designing composite materials because the fiber volume fraction mainly determines mechanical and thermal properties. Conventional Ignition methods are effective for ceramic fiber reinforcing composite materials. However, these methods are not proper for applying to carbon fiber reinforcing composites because of the venerable characteristic against oxidation of carbon fiber. In the research, fiber volume fraction of carbon fiber composites was obtained by a thermogravimetric analysis considering oxidation characteristic of the carbon fiber and the method was compared and verified with the results from microscopic cross section images.

• Composites Research
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• v.31 no.4
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• pp.161-170
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• 2018

Cylindrical composite lattice structures are manufactured by filament winding process. The fiber volume fraction non-uniformity and resin rich layers that can occur in the manufacturing process affect the stiffness and strength of the structure. Through the cross-section examination of the hoop and helical ribs, which are major elements of the composite lattice structure, we observed the fiber volume fraction non-uniformity and resin rich layers. Based on the results of the cross-section examination, the stiffness of the ribs was analyzed through the experimental and theoretical approaches. The results show that the fiber volume fraction non-uniformity and resin rich layers have an obvious influence on the rib stiffness of composite lattice structure.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.583-589
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• 2015

This paper presents a study on the room- and low-temperature impact toughness of hypoeutectoid steels with ferrite-pearlite structures. Six kinds of hypoeutectoid steel specimens were fabricated by varying the carbon content and austenitizing temperature to investigate the effect of microstructural factors such as pearlite volume fraction, interlamellar spacing, and cementite thickness on the impact toughness. The pearlite volume fraction usually increased with increasing carbon content and austenitizing temperature, while the pearlite interlamellar spacing and cementite thickness mostly decreased with increasing carbon content and austenitizing temperature. The 30C steel with medium pearlite volume fraction and higher manganese content, on the other hand, even though it had a higher volume fraction of pearlite than did the 20C steel, showed a better low-temperature toughness due to its having the lowest ductile-brittle transition temperature. This is because various microstructural factors in addition to the pearlite volume fraction largely affect the ductile-brittle transition temperature and low-temperature toughness of hypoeutectoid steels with ferrite-pearlite structure. In order to improve the room- and low-temperature impact toughness of hypoeutectoid steels with different ferrite-pearlite structures, therefore, more systematic studies are required to understand the effects of various microstructural factors on impact toughness, with a viewpoint of ductile-brittle transition temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.421-424
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• 2008

Ultra high strength steel fiber-reinforced concrete is characterized with high tensile strength and ductility. This paper revealed the influence of fiber volume fraction on the tensile softening behaviour of ultra high strength steel fiber-reinforced concrete and developed tensile softening model to predict the deformation capacity by finite element method analysis with experimental results. The initial stiffness of ultra high strength steel fiber-reinforced concrete was constant irrespective of fiber volume fraction. The increase of fiber volume fraction improved the flexural tensile strength and caused more brittle softening behaviour. Finite element method analysis proposed by Uchida et al. was introduced to obtain the tensile softening curve from three point notched beam test results and we proposed the tensile softening model as a function of fiber volume fraction and critical crack width.

• Korean Journal of Materials Research
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• v.29 no.6
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• pp.349-355
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• 2019

This study deals with the microstructure and tensile properties of 600 MPa-grade seismic reinforced steel bars fabricated by a pilot plant. The steel bar specimens are composed of a fully ferrite-pearlite structure because they were air-cooled after hot-rolling. The volume fraction and interlamellar spacing of the pearlite and the ferrite grain size decrease from the center region to the surface region because the surface region is more rapidly cooled than the center region. The A steel bar specimenwith a relatively high carbon content generally has a higher pearlite volume fraction and interlamellar spacing of pearlite and a finer ferrite grain size because increasing the carbon content promotes the formation of pearlite. As a result, the A steel bar specimen has a higher hardness than the B steel bar in all the regions. The hardness shows a tendency to decrease from the center region to the surface region due to the decreased pearlite volume fraction. On the other hand, the tensile-to-yield strength ratio and the tensile strength of the A steel bar specimen are higher than those of the B steel bar with a relatively low carbon content because a higher pearlite volume fraction enhances work hardening. In addition, the B steel bar specimen has higher uniform and total elongations because a lower pearlite volume fraction facilitates plastic deformation caused by dislocation slip.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.4
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• pp.246-250
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• 2021

TFTs technologies with as high mobility as possible is essential for high-performance large displays. TFTs using nanocrystalline silicon thin films can achieve higher mobility. In this work, the change of the crystalline volume fraction at different hydrogen dilution ratios was investigated by depositing nc-Si:H thin films using PECVD. It was observed that increasing hydrogen dilution ratio increased not only the crystalline volume fraction but also the crystallite size. The thin films with a high crystalline volume fraction (55%) and a low defect density (10¹⁷ cm^-3·eV^-1) were used as top gate TFTs channel layer, leading to a high mobility (55 cm²/V·s). We suggest that TFTs of high mobility to meet the need of display industries can be benefited by the formation of thin film with high crystalline volume fraction as well as low defect density as a channel layer.