• Korean Journal of Metals and Materials
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• v.49 no.10
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• pp.754-759
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• 2011

In this study, the interlaminar fracture behaviors of laminated GFRP composites were investigated, and the results could be used for damage tolerance design based on fracture mechanics. Three types of laminated GFRP composites that can be used as high voltage insulating materials in magnet systems were fabricated in order to study the interlaminar fracture behavior according to the molding process. The values of interlaminar fracture toughness for the VPI, prepreg, and HPL laminate were $1.9MPa{\cdot}^{1/2}$, $1.7MPa{\cdot}^{1/2}$, and $2.2MPa{\cdot}^{1/2}$, respectively. HPL laminate showed the best fracture resistance. The failure modes of HPL and VPI were similar to that of an adhesive joint, and prepreg laminates showed partial cohesive failure mode due to internal voids.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2383-2389
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• 2002

This paper describes an experimental study on fatigue life extension by using cold working process in fastener hole of aircraft structure. Cold working process was applied for A12024-7351 specimens by considering the effect of edge margin on fatigue life. It is generally recognized that cold working process offers a protective zone around fastener hole of aluminum aircraft structure due to the residual compressive stresses which lead to retardation of crack growth. Thus this process provides the beneficial effect of increasing the fatigue life of the component. there by decreasing maintenance costs. It has also been successfully incorporated into damage tolerance and structural integrity programs. Cold working specimens were tested at constant amplitude peak cyclic stresses. Fatigue life of cold working specimen compared with that of specimen fabricated with base material. The increase of fatigue life for cold working specimen is discussed by both considering the effect of residual compressive stresses measured by X-ray diffraction technique and quantitative effect of edge margin.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.3-14
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• 2012

This paper describes experimental results on the seismic performance of SHCC (strain-hardening cement composite) infill wall for improving damage tolerance capacity of non-ductile frame. To investigate the effect of tensile strain capacity and cracking behavior of SHCC materials on the shear behavior of SHCC infill wall, three infill walls were fabricated and tested under cyclic loading. The test parameter in this study is a type of cement composites; concrete and SHCCs. The two types of SHCC materials were prepared for infill walls. In order to induce crack damages into the mid-span of the infill wall, each infill wall had two 100-mm-deep-notches on both sides. Test results indicated that SHCC infill walls showed superior crack control capacities and much larger drift ratios at the peak loads than RC (reinforced concrete) infill wall, as expected. In particular, due to the bridging actions of the reinforcing fibers, SHCC matrix used in this study would delay the stiffness degradation of infill wall after the first inclined cracking. Moreover, from the damage classes based on the cracks' maximum width in the infill walls, it was observed that PIW-SHD specimen possessed nearly threefold seismic capacities compared to PIW-SLD specimen. Also, from the results on the strain of diagonal reinforcements, it can be concluded that the SHCC matrix would resist a part of tensile stresses transferred along steel rebar in the infill wall.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.263-271
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• 2005

HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

• Biomolecules & Therapeutics
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• v.23 no.6
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• pp.582-589
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• 2015

Several theories emphasize that aging is closely related to oxidative stress and disease. The formation of excess ROS can lead to DNA damage and the acceleration of aging. Vigna angularis is one of the important medicinal plants in Korea. We isolated vitexin from V. angularis and elucidated the lifespan-extending effect of vitexin using the Caenorhabditis elegans model system. Vitexin showed potent lifespan extensive activity and it elevated the survival rates of nematodes against the stressful environments including heat and oxidative conditions. In addition, our results showed that vitexin was able to elevate antioxidant enzyme activities of worms and reduce intracellular ROS accumulation in a dose-dependent manner. These studies demonstrated that the increased stress tolerance of vitexin-mediated nematode could be attributed to increased expressions of stress resistance proteins such as superoxide dismutase (SOD-3) and heat shock protein (HSP-16.2). In this work, we also studied whether vitexin-mediated longevity activity was associated with aging-related factors such as progeny, food intake, growth and movement. The data revealed that these factors were not affected by vitexin treatment except movement. Vitexin treatment improved the body movement of aged nematode, suggesting vitexin affects healthspan as well as lifespan of nematode. These results suggest that vitexin might be a probable candidate which could extend the human lifespan.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.925-928
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• 2008

Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. To apply SHCC to structural member, SHCC must have economical efficiency and workability as well as own excellent tensile performance. For these purposes, four-point bending and direct tensile tests on SHCC with only hybrid synthetic fibers, total fiber volume fraction, $V_f$, is 1.5%, are carried out. The research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA) and Polyethylene (PE) fibers, and how this affects the composite property, and ultimately its strain-hardening performance. Also, effect of hybrid type and water-cement ratio on the behavior of SHCC was evaluated in this paper.

• Advances in concrete construction
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• v.15 no.3
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• pp.203-213
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• 2023

New techniques, technologies, and materials should be used to design and build sports stadiums. Since this century, much progress has been made in covering the roofs of sports stadiums, and the possibility of accurate computer calculation has been provided for stadiums, so by choosing a new structure, we can double the beauty and resistance of these stadiums. A stadium has an excellent and valuable design when its structure, shell, building, materials, and joinery follow a high architectural idea at all levels and scales. This article examines the mechanical performance of polymer cement strength in the construction of football stadiums, along with their structural knowledge in the form of the best examples in the world. Portland cement is one of the most used materials for constructing football stadiums. However, its production requires spending a lot of money, wasting energy, and damaging the environment. Considering the disadvantages in the production and consumption of concrete in different environments, it is necessary to find alternative materials. It should be used with cheaper, simpler technology, abundant primary resources, energy saving, less environmental damage, and better chemical and physical properties in concrete. High-strength concrete technology is considered a new development in the construction industry of concrete structures. In hardened concrete, strength and durability are two main factors, and as the compressive strength of concrete increases, concrete becomes more brittle. As a result, its tensile strength does not increase in proportion to the increase in compressive strength and has less strain tolerance. For this reason, the need to use is evident from the fibers in high-strength concrete. Fibers are used in concrete to increase tensile strength, prevent crack propagation, and significantly increase softness. The increase with the change of these resistances depends on the strength of concrete without fibers, the shape of fibers, and the percentage of fibers. This cement is obtained from the wastes of chemical and petrochemical industries and the wastes from coal combustion, which have the properties mentioned as substitutes for Portland cement.

• Journal of People, Plants, and Environment
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• v.23 no.6
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• pp.625-636
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• 2020

Background and objects: Soil contamination caused by CaCl₂ that is used to deice slippery roads in winter is now recognized as one of the major causes of damage of roadside plants. The aim of this study is to identify the salt mitigation effects of planting Chrysanthemum zawadskii and using a soil conditioner. Methods: The study was conducted at the site where Pinus densiflora f. multicaulis was planted on the roadside between Konkuk University Sageori and Danwol Samgeori located in Chungju-si. We classified the soils collected from the field experimental site according to the degree of the damage caused by deicing agents and divided the site into six blocks of three 80 × 80 cm plots replicated by treatment type. Three selected plots were treated with loess-balls on the soil surface (high salinity with loess-balls, medium salinity with loess-balls, low salinity with loess-balls) and three were left as an untreated control (H = high salinity, M = medium salinity, L = low salinity). The soil properties were measured including pH, EC and exchangeable cations as well as the growth of Chrysanthemum zawadskiia. Results: In the results of soil analysis, pH before planting Chrysanthemum zawadskiia was 6.39-6.74 and in September, five months after planting, the acidity was reduced to 5.43-5.89. Electrical conductivity (EC) was measured to be H > M > L with the higher degree of damage by deicing agents. The analysis of deicing exchangeable cations showed that the content of Ca²⁺ of soils were significantly correlated to deicing exchangeable cations (Ca²⁺, Na⁺, Mg²⁺) in the shoot part of Chrysanthemum zawadskii. The loess-ball treatment showed a lower content of deicing exchangeable cations than the treatment where Chrysanthemum zawadskiia was planted. Conclusion: In this study, the use of a new system made of loess-balls is proposed as a soil conditioner to protect soils from the adverse effects of road deicing salts. These data suggest that treatment of soil conditioners and planting Chrysanthemum zawadskiia are effective in mitigation of salt stress on the soils damaged by deicing agents.

• Journal of Environmental Science International
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• v.15 no.12
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• pp.1093-1101
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• 2006

In the present study we studied the growth, photosynthetic traits and protective mechanisms against oxidative stress in the primary loaves of cucumber (Cucumis sativus L.) seedlings with or without UV-B treatment. Cucumber seedings were irradiated with UV-B for 10 days in environment-controlled growth chambers. The primary leaves irradiated with UV-B showed reduction in leaf length and decreased biomass production. The reduced biomass production seemed to be due to a negative effect of UV-B radiation on the photosynthetic process. Changes in chemical properties of leaf, such as chi a/b ratio affected photosynthesis. UV-B significantly affected chl b content compared with chi a in the light harvesting complex resulting reduced photosynthetic activity Fv/Fm decreased with an UV-B stress, suggesting that the photosynthetic apparatus, and particularly, PS II was damaged under UV-B stress. Malondialdehyde(MDA) concentration which represents the state of membrane lipid peroxidation Increased significantly under UV-B stress confirming an oxidative stress. UV-B exposure with SA solution(0.1-1.0 mM) can partially ameliorated some of the detrimental effects of UV-B stress. Leaf injuries including loss of chlorophyll and decreased ratio of Fv/Fm were reduced with combined application of UV-B and SA. ABA and JA showed similar mode of action in physiological effects on photosynthetic activities though the levels were lower than those from SA treated plants. Chloroplast ultrastructure was also affected by UV-B exposure. The thickness of leaf tissue components decreased and the number of grana and thylakoids was reduced in chloroplast applied UV-B or SA alone. At combined stress granal and stromal thylakoids were less affected. The leaves under combined stress acquired a significant tolerance to oxidative stress. From these results, it can be suggested that SA may have involved a protective role against UV-B induced oxidative damage.

• Current Industrial and Technological Trends in Aerospace
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• v.7 no.2
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• pp.76-84
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• 2009

In this review an attempt is made to give the background to the current trends in foreign developments in the ceramic matrix composites for space vehicles. The lightweight and high temperature specific modulus properties of ceramic composites have continued to develop for designing advanced propulsion structures and for increasing space vehicle performances. Those applications require advanced materials with good resistance to high temperatures, to oxidation environments and to mechanical stresses. The advantages of ceramic matrix composites are the low specific weight, the high specific strength over a wide temperature ranges, and their good damage tolerance compared to tungsten, pyrographites and polycrystalline graphites. Due to these advantages ceramic matrix composites are currently used in rocket engine chamber, nozzle, solar array, radar antenna, mirror support structures, hypersonic leading edge articles, heat shields, reentry vehicle nose tips, and radiators for spacecraft. Various processes are discussed together with examples of current application so that some of the advanced technologies can be possibly applied to Korean space technology.