• Journal of the Korea Institute of Building Construction
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• v.8 no.1
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• pp.43-48
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• 2008

Fifteen concrete specimens were mixed and tested to explore the significance and limitation of appling the polyvinyl alcohol (PVA) fiber and steel fiber with end hook to concrete. Main parameters investigated were volume fraction and length of the fibers. The measured mechanical properties of fiber reinforced concrete are analyzed according to the equivalent fiber amount index explaining the adding amount and length of fibers. Test results showed that compressive strength of fiber reinforced concrete was higher than that of concrete with no fiber by $10{\sim}20%$. The normalized splitting tensile strength and flexural strength of PVA fiber reinforced concrete were similar to those of concrete with no fiber, whereas those of steel fiber reinforced concrete increased with the increase of the equivalent fiber amount index. In particular, much higher ductile behavior was observed in steel fiber reinforced concrete than in PVA reinforced concrete, indicating that the slope of descending branch of load-displacement relationship of steel fiber reinforced concrete decreased with the increase of the volume fraction and length of the fiber.

• Steel and Composite Structures
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• v.30 no.6
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• pp.603-615
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• 2019

In the present work, free vibration of beams made of imperfect functionally graded materials (FGMs) including porosities is investigated. Because of faults during process of manufacture, micro voids or porosities may arise in the FGMs, and this situation causes imperfection in the structure. Therefore, material properties of the beams are assumed to vary continuously through the thickness direction according to the volume fraction of constituents described with the modified rule of mixture including porosity volume fraction which covers two types of porosity distribution over the cross section, i.e., even and uneven distributions. The governing equations of power law FGM (P-FGM) and sigmoid law FGM (S-FGM) beams are derived within the frame works of classical beam theory (CBT) and first order shear deformation beam theory (FSDBT). The resulting equations are solved using separation of variables technique and assuming FG beams are simply supported at both ends. To validate the results numerous comparisons are carried out with available results of open literature. The effects of types of volume fraction function, beam theory and porosity volume fraction, as well as the variations of volume fraction index, span to depth ratio and porosity volume fraction, on the first three non-dimensional frequencies are examined in detail.

• Steel and Composite Structures
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• v.23 no.3
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• pp.251-261
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• 2017

In this paper, thermal effect on the vibration and stability of initially stressed sandwich plates with functionally graded material (FGM) face sheets is analyzed. Material properties of FGM face sheet are graded continuously in the thickness direction. The variation of FGM properties assumes a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of arbitrarily initially-stressed sandwich plates including the effects of transverse shear deformation and rotary inertia are derived. The initial stress is taken to be a combination of a uniaxial extensional stress and a pure bending stress in the examples. The eigenvalue problems are formed to study the vibration and buckling characteristics of simple supported initially stressed FGM/metal/FGM plates. The effects of volume fraction index, temperature rise, initial stress and layer thickness of metal on the natural frequencies and buckling loads are investigated. The results reveal that the volume fraction index, initial stresses and layer thickness of metal have significant influence on the vibration and stability of sandwich plates with FGM face sheets.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.129-139
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• 2020

In this piece of work, carbon nanotubes motion equations are framed by Kelvin's method. Employment of the Kelvin's method procedure gives birth to the tube frequency equation. It is also exhibited that the effect of frequencies is investigated by varying the different index of polynomial function. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. Throughout the computation, it is observed that the frequency behavior for the boundary conditions follow as; clamped-clamped, simply supported-simply supported and these frequency curves are higher than that of clamped-free curves. Computer software MATLAB is utilized for the frequencies of single-walled carbon nanotubes.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.3
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• pp.28-36
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• 2010

Today We have three full series of the annals of Joseon Dynasty. Taebaeksan volume which is one of them shows comparatively good maintenance but Taebaeksan volume also decomposed in patches. The size of cover and inner paper were increased in late Joseon Dynasty, but the weight, thickness and basis weight bears no relation to each other. The oxidation index of paper in annals of pre-periods of King Sunjo shows very high value. After the annals of King Sunjo, the oxidation index of paper is very similar to today's Hanji. L.a.b values of inner paper in the Taebaeksan volume are similar generally. The average length of fiber using image analysis soft ware is 8.08~9.92 mm, that like immediate value of measurement. The air fraction of fiber's range is 1.20~2.12%. It lower than today's Hanji. After considering the factors of the length of fiber, air fraction and FE-SEM, we reached that no difference between raw material of inner paper in the Taebaeksan volume.

• Steel and Composite Structures
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• v.37 no.5
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• pp.621-632
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• 2020

This research deals with the study of vibrational behavior of armchair and zigzag single-walled carbon nanotubes invoking extended Love shell theory. The effects of different physical and material parameters on the fundamental frequencies are investigated. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. To discretize the governing equation in eigen-value form, wave propagation approach is developed. Complex exponential functions have been used and the axial model depends on boundary condition that has been described at the edges of carbon nanotubes to calculate the axial modal dependence. Computer software MATLAB is utilized for the frequencies of single-walled carbon nanotubes and current results shows a good stability with comparison of other studies.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• Korea-Australia Rheology Journal
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• v.15 no.3
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• pp.125-130
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• 2003

The emulsion stability of cosmetic creams based on the water-in-oil (W/O) high internal phase emulsions (HIPEs) containing water, squalane oil and cetyl dimethicone copolyol was investigated with various compositional changes, such as electrolyte concentration, oil polarity and water phase volume fraction. The rheological consistency was mainly destroyed by the coalescence of the deformed water droplets. The slope change of complex modulus versus water phase volume fraction monitored in the linear viscoelastic region could be explained with the resistance to coalescence of the deformed interfacial film of water droplets in concentrated W/O emulsions: the greater the increase of complex modulus was, the more the coalescence occurred and the less consistent the emulsions were. Emulsion stability was dependent on the addition of electrolyte to the water phase. Increasing the electrolyte concentration increased the refractive index of the water phase, and thus decreased the refractive index difference between oil and water phases. This decreased the attractive force between water droplets, which resulted in reducing the coalescence of droplets and increasing the stability of emulsions. Increasing the oil polarity tended to increase emulsion consistency, but did not show clear difference in cream hardness among the emulsions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.109-115
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• 2015

High performance fiber reinforced cementitious composite (HPFRCC) can provide high fracture energy absorption as well as high strength with high fiber volume fraction. The increased fracture energy helps resisting high frequency loadings, such as earthquake, impact or blast. This study investigates the flexural performance of slurry infiltrated fiber concrete (SIFCON), one of the important HPFRCC, with respect to varying fiber volume fraction. The maximum fiber volume fraction was 8.0 % and reduced to 6.0% by 0.5% and the maximum volume fraction is obtained by packing fibers with simple tapping by hands. The used fiber was a steel fiber with the length 30 mm and the diameter of 0.5 mm. The flexural strengths were 48.7 MPa at 8.0 % and 22.8 MPa at 6.0 %. The measured flexural strength is much higher compared to other cememtitious composite materials but decreased proportional to the fractions. This result implies that for SIFCON considered herein the reduced amount of steel fibers may affect its flexural performance in a negatively way. The flexural toughness, an index to represent the fracture energy absorption, also decreased with the reduced fiber amount.

• Advances in nano research
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• v.9 no.4
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• pp.251-261
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• 2020

In this article, vibration attributes of single walled carbon nanotubes based on Galerkin's method have been investigated. The influence of power law index subjected to different end supports has been overtly examined. Application of the Hamilton's variational principal leads to the formation of partial differential equations. The effects of different physical and material parameters on the fundamental frequencies are investigated for armchair and zigzag carbon nanotubes with clamped-clamped, simply supported and clamped-free boundary conditions. By using volume fraction for power law index, the fundamental natural frequency spectra for two forms of Single-Walled Carbon Nanotubes (SWCNTs) are calculated. The influence of frequencies against length-to-diameter ratios with varying power law index are investigated in detail for these tubes. MATLAB software package has been utilized for extracting tube frequency spectra. The obtained results are confirmed by comparing with available literature.