• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.98-105
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• 2017

In this study, the fiber blending ratio and strain rate effect on the tensile behavior of hybrid fiber reinforced cement composite was evaluated. Hooked steel fiber and polyvinyl alcohol fiber were used for reinforcing fiber. The fiber blending ratio of HSF+PVA were 1.5+0.5, 1.0+1.0 and 0.5+1.5vol.%. As a results, the tensile strength, strain capacity and fracture toughness of the hooked steel fiber reinforced cement composites were improved by the increase of the bond strength of the fiber and the matrix according to increase of strain rate. However, the tensile stress sharply decreased after the peak stress because of the decrease in the number of straightened pull-out fibers by micro cracks in the matrix around hooked steel fiber. On the other hand, PVA fiber showed cut-off fracture at strain rate $10^{-6}/s$ with multiple cracks. However, at the strain rate $10^1/s$, the multiple cracks and strain capacity were decreased because of the pull-out fracture of PVA fiber. The HSF1.5PVA0.5 shown the highest tensile strength because the PVA fiber suppressed the micro cracks in the matrix around the hooked steel fiber and improved the pull-out resistance of hooked steel fiber. Thus, DIF of strain capacity and fracture toughness of HSF1.5PVA were greatly improved. In addition, the synergistic response of fracture toughness was positive because the tensile stress was slowly decreased after the peak stress by improvement of the pull-out resistance of hooked steel fiber at strain rate $10^1/s$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.401-406
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• 2008

This study can be used to produce structurally efficient recycled PET fiber from used waste PET bottles and evaluated the bond performance of the three type of recycled PET fiber and cement matrix. Also, the flexural tests were performed on concrete reinforced using the three type of recycled PET fibers. The test results showed that the recycled PET fiber was significantly increased bond strength. The flexural test results are demonstrated that recycled PET fibers improved the flexural toughness of concrete. Based on the bond and flexural test results, the bond and flexural performance of embossed type recycled PET fibers were significantly better than those of the other shape fibers.

• Journal of the Korean Geosynthetics Society
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• v.7 no.4
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• pp.37-45
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• 2008

A pilot test using environmentally friendly drains, was carried out to evaluate their applicability potential in the field. The pilot test site was divided into 5 different areas, with several combinations of vertical and horizontal drains installed for evaluation. Conventional natural fiber drains (FDB), new developed straw drain board (SDB) and plastic drain board (PDB) were used as vertical drains, while sand and fiber mats were used as horizontal drains. Surface settlement rates and excess pore pressure generation/dissipation tendency of PDB and FDB are almost identical except those of SDB. Cone tip resistance obtained from cone penetration test measured at the end of 1st consolidation stage for upper soft layer definitely increased irrespective of types of vertical drains. The monitoring and site investigation test data obtained at the pilot test site prove the vertical natural fiber drains can be used as substitutes of conventional plastic and sand material.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1322-1325
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• 2005

The main objectives of this research work are to develop conductive glass fiber woven roving and carbon fiber unidirectional fabric composite materials and to determine their electromagnetic shielding effectiveness(EMSE). Epoxy is the matrix phase and glass, carbon fiber are the reinforcement phase of the composite material. Carbon black are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of carbon black in the composite material is varied by changing the carbon black composition, woven roving and unidirectional (fabric) structure. The EMSE of various fabric composites is measured in the frequency range from 300MHz to 800MHz. The variations of EMSE of woven roving and unidirectional composites with fabric structure, metal powder composite are described. Suitability of conductive fabric composites for electromagnetic shielding applications is also discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.120-126
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• 2018

In the present study, the multi-nozzle electrospinning process is investigated for the fabrication of uniform polymer nanofiber mats. Electrospinning has been one of the simple and efficient methods to manufacture polymer nanofibers and their mats. Although a typical electrospinning has many advantages such as simple system and operation, various materials, and cost-effectiveness, a relatively low productivity prevents it from being used in practical applications. Thus, the multi-nozzle electrospinning system with the adjustable nozzle position and rotating drum collector is designed and produced in this study. In particular, the effects of the inter-nozzle distance and spatial arrangement of nozzles on the uniformity of the electrospun nanofibers are investigated. With this multi-nozzle electrospinning process, the maximum flow rate of the supplied polymer solution for a uniform electrospinning increases, which indicates the enhanced productivity.

• Elastomers and Composites
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• v.34 no.3
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• pp.247-252
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• 1999

Rubber related geosynthetics(GS) as reinforcement and water barrier materials were manufactured by thermal bonding method and examined the their performance for applications to civil and environmental engineering fields. The spunbonded polyester nonwoven, fiber glass mat and fabric type geogrid of a high tenacity polyester filament were used as matrix and polyester film, elastomeric bitumen with SBS polymer and asphalt were used as reinforcements to manufacture the rubber related geosynthetics. A fiber glass mat and geogrid matrix GS showed more excellent mechanical properties and nonwoven and elastomeric bitumen matrix showed the more excellent permittivity. Softening points of rubber and asphalt mixture showed no difference and dimensional stability at high temperature, $120^{\circ}C$, represented no significant shrinkage. Resistance to ultraviolet of rubber related geosynthetics showed no visible alteration.

• Journal of the Korean Geotechnical Society
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• v.22 no.3
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• pp.13-21
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• 2006

Geosynthetic damage has attracted a major attention since the introduction of geotextiles for civil engineering applications. In this study 3 pilot trial embankments were carried out to investigate the behaviours of reinforced embankments over soft cohesive soils and to find the optimum methodology of embankments over soft soils. As the seamed part of polyester mat (PET, tensile strength 15 ton) used in the first full-scale field test was ruptured under progressing rotational slope failure because of unexpectedly rapid construction of embankments, the excessive pore water pressures were measured. On the soil behavior where tension explosion of mat was continued, pore pressure larger than the one caused by embankment height was measured. Especially, at the depth of 5.0 m under the ground pore pressure increased over long term. It was discussed with respect to the height of embankment and heaving behavior of soft soils.

• The Journal of the Korea Contents Association
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• v.22 no.2
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• pp.80-87
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• 2022

Most of the disaster relief items provided to sufferers and temporary evacuees that are supposed to be victims in Korea are not suitable for the shelter environment of temporary housing facilities, and are not satisfactory because they do not have the functions, proper size and types. The purpose of this study is to analyze the user needs of emergency rescue relief items by presenting problems about the use environment and to develop the variable air mattresses which are based on disaster prevention design. In order to secure objectivity such as usability, convenience, and durability, research data are limited. However, the difficulty of mass spreading of conventional fiber mat and the functional disadvantages of foam plastic mat are solved by adopting variable air mattresses. The variable air mattresses are expected to help rehabilitate people by helping victims of physical tiredness, illness worsening, poor sleep, and life instability that can happen during long-term shelter life.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.709-716
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• 2005

The objective of this study is to develop a high ductile fiber reinforced mortar, ECC(Engineered Cementitious Composite) with using raw material commercially available in Korea. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties in a matrix and the fracture toughness of mortar matrix respectively, which are used for designing mix proportion suitable for achieving strain-hardening behavior at a composite level. Test results showed that the properties tended to increase with decreasing water-cement ratio. A high ductile fiber reinforced mortar has been developed by employing micromechanics-based design procedure. Micromechanical analysis was initially peformed to properly select water-cement ratio, and then basic mixture proportion range was determined based on workability considerations, including desirable fiber dispersion without segregation. Subsequent direct tensile tests were performed on the composites with W/C's of 47.5% and 60% at 28 days that the fiber reinforced mortar exhibited high ductile uniaxial tension property, represented by a maximum strain capacity of 2.2%, which is around 100 times the strain capacity of normal concrete. Also, compressive tests were performed to examine high ductile fiber reinforced mortar under the compression. The test results showed that the measured value of compressive strength was from 26MPa to 34 MPa which comes under the strength of normal concrete at 28 days.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.3
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• pp.240-245
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• 2001

The tensile strength and failure mechanisms of glass fiber polypropylene (GF/PP) composites are investigated in the temperature range from ambient to 8$0^{\circ}C$. The tensile strength increases as fiber volume fraction ratio increase. The tensile strength shows a maximum at ambient temperature, and it tens to decrease as temperature goes up. Major failure mechanisms of GF/PP composites can be classified as fiber matrix debonding, fiber pull-out, delamination and matrix deformation.