• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.11
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• pp.48-53
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• 1997

Volume hologram was recorded using reference beam form optical fiber taper. A singel mode fiber was chemically etced to make a taper structure, and we showed experimentally that the referencing by the irregular beam pattern from this taper structure could increase the storage density of photorefractive volume hologram. The spatial selectivity of the volume hologram with this method was increased by two times compared to the normal single mode fiber referencing case. A theoretical analysis with randomly phased plane model also confirmed the results.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.401-409
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• 2005

In this study, reinforced dual concrete beam (RDC beam) composed of steel fiber reinforced concrete (SFRC) in the tension part and normal strength concrete (NSC) in the compression and remaining part is proposed. It is the epochal structural system that improves the overall structural performances of beam by partially superseding the steel fiber reinforced concrete in the lower tension part of conventional reinforced concrete beam (RC beam). Flexural and shear tests are performed to prove the structural excellence of RDC beam in comparison with RC beam. An analytical method is proposed to understand the flexrual behavior and is compared to experimental results. And for shear behavior, experimental results are compared to empirical equations predicting the ultimate shear strength of full-depth fiber reinforced concrete beam to examine the behavior of RDC beam under shear. From this studies, it is proved that RDC beam has more superior structural performance than RC beam, and the analytical method for flexural behavior agrees well with experimental results, and the partial-depth fiber reinforcements have no noticeable effect on ultimate shear strength but it is considerably effective to control and prevent evolutions of crack.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.867-873
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• 2004

It has been known that debonding failures between CFS(Carbon Fiber Sheet) and concrete in the strengthened RC beams are initiated by the peeling of the sheets in the region of combined large moment and shear forces, being accompanied by the large shear deformation after flexural cracks. These shear deformation effects are seldom occurred in small-scale model tests, but debondings due to the large shear deformation effects are often observed in a full-scale model tests. The premature debonding failure of CFS, therefore, must be avoided to confirm the design strength of full-scale RC beam in strengthening designs. The reinforcing details, so- called 'U-Shape fiber wrap at mid-span' which wrapped the RC flexural members around the webs and tension face at critical section with CFS additionally, were proposed in this study to prevent the debonding of CFS. Other reinforcing detail, so called 'U-Shape fiber wrap at beam end' were included in this tests and comparisons were made between them.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.259-263
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• 2010

Carbon fibers are used as a reinforcement material in an epoxy matrix in advanced composites due to their high mechanical strength, rigidity and low specific density. An important aspect of the mechanical properties of composites is associated to the adhesion between the surface of the carbon fiber and the epoxy matrix. This paper aimed to evaluate the effects of electron beam irradiation on the physicochemical properties of carbon fibers to obtain better adhesion properties in resultant composite. Chemical structure and surface elements of carbon fiber were determined by FT-IR, elemental analysis and X-ray photoelectron spectroscopy, which indicated that the oxygen content increased significantly with increasing the radiation dose. Thermal stability of the carbon fibers was studied via the thermalgravimetric analysis. Surface morphology of carbon fiber was analyzed by scanning electron microscope. It was found that the degree of surface roughness was increased by electron beam irradiation.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.4
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• pp.3921-3930
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• 1975

This research was carried out to investigate several mechanical characteristics of pre-stressed steel beams. The configuration of specimens used for this study were as follows; a cover plate having permissible fiber stress of 4,000 kg/$\textrm{cm}^2$ was welded at bottom having the allowable bending stress 2500 kg/$\textrm{cm}^2$ steel beam, the section ratios of pre-stressed steel beam and cover plate were 0.5 and 0.6. Adopted pre-stresses were 0%, 50%, and 100% of an allowable fiber stress of a steel beam. The results obtained from the study may be summarized as follows; 1. The elastic range of a beam was increased by the application of pre-stress to the beam, which leads to a lighter section. 2. The permissible moment capacity of a pre-stressed steel beam was greated than that of a steel beam without pre-stressing. 3. The equivalent allowable stress induced by adopting the different section ratio of pre-stressed beam to cover plate were figured out 4. The optimum value of section ratio of beam and cover plate was 0.3 to 0.4 in case of a 1.5m span composite beam, a combination of an allowable stress 2,500kg/$\textrm{cm}^2$ steel beam and a permissible fiber stress 4,000 kg/$\textrm{cm}^2$ steel cover plate, was used. 5. The magnitude of the pre-stress was desirable to be same as the allowable stress of a steel beam. 6. It was concluded that if the construction techniques in the field are developed and improved, the practicing of pre-stress to the steel structure has a promising future.

• Journal of Radiation Industry
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• v.8 no.1
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• pp.53-57
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• 2014

The kenaf is quickly developing as a renewable resource. Kenaf can be grown under a wide range of weather conditions. Modification of kenaf fiber by graft polymerization provides a significant route to alter the chemical properties, including surface hydrophilicity or hydrophobicity. In this study, kenaf fiber surfaces were grafted with acrylic acid as a hydrophilic group using electron beam irradiation. The grafting rate increased with an increase in grafting time. The FT-IR results confirmed that acrylic acid was successfully grafted onto the kenaf fibers. The wettability of the kenaf fiber was increased, accompanied by acylic acid grafting on the fiber surface. According to the permeability test result, it was found that acrylic acid grafted kenaf fiber reinforced cement composite was more reduced than non-grafted kenaf fiber reinforced cement composite.

• Advances in Computational Design
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• v.8 no.2
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• pp.113-131
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• 2023

The use of fibers has been commonly considered in engineered cementitious composites, but their behavior with coarse aggregate in concrete has not been studied significantly, which is needed to meet structural performance objectives for design, such as ductility. This research analyzes the behavior of fiber-reinforced concrete with coarse aggregate with 0.62%, 1.23%, and 2% PVA (Polyvinyl-alcohol) content, varying the maximum aggregate size. Tensile (direct and indirect) and compressive concrete tests were performed. The PVA fiber addition in coarse aggregate concrete increased the ductility in compression, especially for the fiber with a larger aspect ratio, with a minor impact on strength. In addition, the tensile tests showed that the PVA fiber increased the tensile strength of concrete with coarse aggregate and, more significantly, improved the ductility. A selected mixture was used to build short and slender reinforced concrete beams to assess the behavior of structural members. PVA fiber addition in short beams changed the failure mode from shear to flexure, increasing the deflection capacity. On the other hand, the slender beam tests revealed negligible impact with the use of PVA.

• Composites Research
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• v.30 no.2
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• pp.158-164
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• 2017

The fiber metal laminate is a type of hybrid materials laminated thin metallic sheets with fiber reinforced plastic sheets. The laminate has been researched or applied in automotive and aerospace industries due to their outstanding impact absorbing performance in view of light weight aspect. Specially, the replacement of side-impact beam as the fiber reinforced plastic has been researched actively. The objective of this paper is the primitive investigation in the development of side-door impact beam using the fiber metal laminate. First, the three-point bending simulations were conducted to decide the shape of impact beam using the numerical analysis. Next, two cases impact beam (pure DP 980 and fiber metal laminate) were installed in the side-door, and then the bending tests (according to FMVSS 214S) were simulated using the numerical analysis. It is noted that the side-door impact beam can be replaced with the fiber metal laminate sufficiently based on the numerical analysis results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.18-24
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• 2016

The purpose of this study is to induce the ductile behavior of the Ultra High Perfomance Concrete Reinforced I beam by substituting the part of steel fiber for bundle of reinforcing bars. Experiment of flexural behavior of the Ultra High Performance Concrete I shaped beam with the combination of the steel fiber and bundle of reinforcement bars was carried out. The volume fractions of steel fiber are 0%, 0.7%, 1%, 2%. The bundle of reinforcing bars and prestressing wire are used to restrain the concrete in compression zone. Length of bundle of reinforcing bar and prestressing wire is the one of test factors. The 9 Reinforced UHPC I shaped beam were made with these test factors. Not only steel fiber but also bundle of longitudinal reinforcing bar has effect to induce the ductile behavior of Reinforced UHPC I beam. The combination of 0.7% or 1.0% steel fiber and bundle of reinforcing bar showed the effective ductile behavior of I beam. The relationship of load-deflection and the crack pattern indicate the usefulness of the bundle of the longitudinal bar which has small diameter with close arrangement each other.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.109-118
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• 2008

Carbon fiber reinforced polymer(CFRP) can be bonded to the soffit of a concrete beam as a means of repairing and strengthening the beam. In such beams, materials, concrete and carbon fiber sheets, are different in coefficient of thermal expansion. Consequently, interfacial shear stresses can be increased and debonding failure may occur at the plate ends due to temperature rising. This paper presents a method of approximate closed-form solutions for the interfacial shear stresses and conducts a beam test to compare the numerical results. In case of temperature rising over $30^{\circ}C$, interfacial stress of 0.91MPa is occurred at the end of sheet. Therefore, using carbon fiber sheet for strengthening the concrete beam, it is necessary to consider the thermal effects and to evaluate the long time behavior of the concrete beam by temperature change.