• Korean Journal of Agricultural Science
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• v.12 no.2
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• pp.292-308
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• 1985

This study was performed to obtain the basic data which can be applied to the use of foamed mortars using foaming agent of prefoamed type. The data was based on the properties of foamed mortars depending upon various mixing ratios of cement to fine aggregates, flow values and foam-cement ratio to compare those of cement mortar. The results obtained were summarized as follow; 1. At the mixing ratio of 1:0 and the foam-cement ratio of 6.00%, the increasing rate of water-cement ratio was 25% by flow $200{\pm}5mm$, 28% by flow $240{\pm}5mm$ and 32% by flow $280{\pm}5mm$. But it decreased as the mixing ratio gets poorer. The result showed that water amount increased because of the high viscosity caused by the increase of foam-cement ratio. The decrease of water-cement ratio was the greatest when the foam-cement ratio was 1.50%. 2. Absolute aridity bulk density of foamed mortars decreased with the increase of foam-cement ratio and the decrease of flow values. 3. Generally, compressive, tensile and bending strenghs of foamed mortars decreased with the decrease of flow values and the increase of foam-cement ratio. 4. The compressive strength was in proportion to tensile strength. It was estimated that the compressive strength was 8.8 times of tensile strength. The compressive strength was in proportion to bending strength. It was estimated that the compressive strength was 4.0 times of bending strength. The bending strength was in proportion to tensile strength. It was estimated that the bending strength was 2.1 times of tensile strength. 5. At the mixing ratio of 1:1 the lowest absorption rates were showed by foamed mortars, respectively. It was significantly higher at the early stage of immersed water.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.3
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• pp.29-34
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• 2008

Purpose: In this study, we compared the physical properties of the compositions that were mixed with basic materials of HEMA (2-Hydroxyethyl methacrylate)/Silicone and BMA (Butyl methacrylate), MMA (Methyl methacrylate) by making the silicone contact lens. Method: Each sample of contact lenses was fabricated by cast mould method. We analyzed results by using average values of physical property of each sample. Results: In the composition of HEMA/Silicone/BMA, water contents of samples showed the value from 24.69% to 29.26%. Ultimate strength of samples showed the value from 0.109 kgf to 0.263 kgf. In the composition of HEMA/Silicone/MMA, swelling ratio of samples showed the value from 13.56% to 14.83%. Water contents of samples showed the value from 25.61% to 29.33%. Ultimate strength of samples showed the value from 0.107 kgf to 0.286 kgf. Conclusions: The compositions of percents of silicone were ranged from 0.20% to 11.50% and the composition percent of BMA and MMA was 5.15% in total. Swelling ratio and water contents increased with decreasing of BMA (Butyl methacrylate) and MMA (Methyl methacrylate) percent. In the composition of HEMA/Silicone/MMA, the values of ultimate strength increased with increasing of silicone percent to 4-MMA sample. In the composition of HEMA/Silicone/BMA, the values of ultimate strength decreased with increasing of silicone percent.

• Composites Research
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• v.36 no.5
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• pp.355-360
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• 2023

Epoxy-based carbon fibers reinforced plastic (CFRP) exhibit limitations in their suitability for industrial applications due to high brittleness characteristics. To address this challenge, extensive investigations are underway to enhance their toughness properties. This research focuses on evaluating the toughening mechanisms achieved by Polyamide 6 particles(p-PA6) and Carboxyl-Terminated Butadiene-Acrylonitrile (CTBN) elastomer, with a specific emphasis on utilizing minimal additive quantities. The study explores the impact of varying concentrations of p-PA6 and CTBN additives, namely 0.5, 1, 2.5, and 5 phr, through comprehensive Mode I fracture toughness and tensile strength analyses. The inclusion of p-PA6 demonstrated improvements in toughness when introduced at a relatively low content of 1phr. This improvement manifested as a sustained fracture behavior, contributing to enhanced toughness, while simultaneously maintaining the material's tensile strength. Furthermore, the investigation revealed that the incorporation of p-PA6 affected in particle aggregation, thus influencing the overall toughening mechanism. Incorporation of CTBN, an elastomeric modifier, exhibited a pronounced increase in fracture toughness at higher concentrations of 2.5 phr and beyond. However, this increase in toughness was accompanied by a reduction in tensile strength, resulting in fracture behavior similar to conventional CFRP exhibiting brittleness. The synergy between pPA6, CTBN and CFRP appeared to marginally enhance tensile strength under specific content conditions. As a result of this study, optimized conditions for the application of the p-PA6, CTBN toughening technology have been identified and established.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.97-104
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• 2023

The aim of this study was to produce polymer cement composites (PCCs) composed of polymer dispersion and cement as crack repair materials for RC structures, and to investigate their fundamental properties. The test mixtures for the study were based on EVA and SAE polymer dispersions, and the water-cement ratio was determined while varying the polymer-cement ratio(P/C) in four different levels (20%, 60%, 80%, and 100%) to achieve the desired viscosity of PCCs considering their fillability as crack repair materials. Additionally, silica fume was incorporated into P/C 80% and 100% specimens to enhance their stiffness. The basic properties of PCCs as crack repair materials, such as viscosity, flowability, fillability, tensile strength, elongation, and modulus of elasticity, were examined. The results showed that P/C depending on the type of polymer significantly affected the viscosity and flowability, and appropriate w/c ratios were needed to achieve the desired viscosity for the mixture design with consideration of fillability as crack repair materials for RC structures. All designed mixtures in this study exhibited excellent fillability. The tensile strength and elongation of PCCs satisfied the KS regulation for cement- polymer modified waterproofing coatings. The incorporation of silica fume improved the tensile strength and modulus of elasticity of PCCs. Depending on the type of polymer, mixtures using SAE showed better fundamental properties as crack repair materials for RC structures compared to those using EVA. In conclusion, SAE-based P/C 80% or 100% with the addition of up to 30% silica fume can be recommended as suitable mixtures for crack repair of RC structures.

• The korean journal of orthodontics
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• v.35 no.4 s.111
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• pp.262-274
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• 2005

Tooth movement is a result of mutual physiologic responses between the periodontal ligament and alveolar bone stimulated by mechanical strain. The PDL cell and osteoblast are known to have an influence on bone formation by controlling collagen synthesis and alkaline phosphatase activation. Moreover. recent studies have shown that the PDL cell and osteoblast release osteoprotegerin (OPG) and the receptor activator of nuclear factor ぉ ligand (RANKL) to control the level of osteoclast differentiation and activation which in turn influences bone resorption. In this study. progressively increased, continuous tensional force was applied to PDL cells. The objective was to find out which kind of biochemical reactions occur after tensional force application and to illuminate the alveolar bone resorption and apposition mechanism. Continuous and progressively increased tensile force was applied to PDL cells cultured on a petriperm dish with a flexible membrane The amount of $PGE_2$ and ALP synthesis were measured after 1, 3, 0 and 12 hours of force application. Secondly RT-PCR analysis was carried out for OPG and RANKL which control osteoclast differentiation and MMP-1 -8, -9, -13 aud TIMP-1 which regulate the resolution of collagen and resorption of the osteoid layer According to the results. we concluded that progressively increased, concluded force application to human PDL cells reduces $PGE_2$ synthesis, and increases OPG mRNA expression.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.47-55
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• 2008

In this paper, comparisons are presented on the predicted tensile strains which can affect the fatigue life of a thin asphalt concrete (AC) pavement near the surface of pavement from three-dimensional (3D) finite element (FE) using 3D measured tire contact stresses of a radial tire and a bias ply tire and a layered linear elastic program (BISAR). The objective was to analyze the stress distributions for a 11R22.5 radial tire and a $10{\times}20$ bias ply tire, and to compare the predicted tensile strains at the top and bottom of AC surface using different analysis methods. The results show that the stress distributions of two tires are similar but the 11R22.5 radial tire has much higher vertical contact stress than that of the $10{\times}20$ bias ply tire. The predicted tensile strains at the bottom of AC layer under the center of tire showed higher value by BM (BISAR with the measured contact area) method, which the measured tire contact area is used in a layered elastic program, while the tensile strain at the top of AC surface of 3.5cm offset distance from tire edge by 3D FE analysis showed the highest values among three analysis methods.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.59-65
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• 2012

The purpose of this study is to analyze the direction of slope sliding that occurred at the highland ${\bigcirc}{\bigcirc}$ district in the Samcheok coalfield, using geological and structural detail surveys. The study area is dominated by the Paleozoic Pyong-an Group, and sliding is concentrated in zones of alternating sandstone and shale beds in the Geumcheon and Jangsung Formations. Discontinuities in the area have a strike of NE-SW and dip at 30~$80^{\circ}$ to the NW and 40~$80^{\circ}$ to the SE. However, some have strikes of NW-SE. In slide area group 1 (P1 to P4), en echelon tension gashes were caused by shearing. The surface in the areas of group 2 (P5 to P7) and group 3 (P8 and P9) is marked by step-type tension cracks that formed due to extension. This phenomenon caused anticlockwise rotation of the sliding slope. Otherwise, the cutting of the road side through the eastern slope of the mountain contributed to surface sliding due to geographical equilibrium loss.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.407-418
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• 2014

As a continuing work of previously conducted standard tension tests, full-scale flexural tests were conducted in this study to assess the structural performance the CJP groove welded joints connecting thick HSA800 plates. Two welding electrodes were available at the time of this experimental research; one was GMAW-based electrode A and the other FCAW-based electrode B. Three full-scale box-type beam specimens with single bevel- and V-groove CJP welded joints were fabricated from 60mm and 25mm thick HSA800 plates according to the AWS-prequalified groove welded joint details. In designing the specimens, all possible limit states like local and lateral torsional buckling were carefully controlled in order to induce flexural plastic yielding or eventual joint fracture. All the CJP joints made by both welding electrodes showed satisfactory performance and were able to transfer the tensile flange forces higher than that corresponding to the measured tensile strength of HSA800 flange plates. However, it should be noted that, during fabrication, serious concerns about the welding efficiency and workability of the GMAW-based electrode were raised by a certified welder. The fracture occurred at the unbeveled (or vertical) interface between the weldment and the base metal when the GMAW-based electrode was used in the single-bevel joint, implying the possibility of insufficient melting. Thus, the FCAW-based electrode B is again recommended as the choice of welding electrode for HSA800 plates. The limited test data of this study implies that the V-groove CJP joint should be used in favor of the single bevel CJP joint, if possible.

• The korean journal of orthodontics
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• v.26 no.3
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• pp.317-324
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• 1996

This study was conducted to evaluate the tensile bond strength of three commercially available glass ionomer cements as orthodontic bracket adhesives. 120 premolars extracted for orthodontic treatment were prepared for bonding and standard edgewise brackets were bonded with Shofu Glaslonomer Cement (Shofu Co., U.S.A.), GC Fuji ItGC Co., Japan), KETAC-CEM(ESPE Co., West Germany) with different P/L ratio. The tensile bond strength was tested by Instron testing device after 24hours and 3months from bonding. After debracketing, bracket bases were examined to determine the failure sites. The results of this study were as follows: 1. KETAC CEM showed the highest bond strength other than measurement after 24 hours and at its original P/L ratio, and seemed to have clinically a proper bond strength. It seemed, however, that both Shofu Giaslonomer Cement and GC Fuji I had an inappropriate bond strength. 2. The incorporation of additional powder into the mixture improved the tensile bond strength. 3. Prolonged storage time improved the tensile bond strength. 4. Of the failure, failure occured at the tooth-adhesive interface(54.2%) was the most common type. The second type of failure(36.7%) was combination type, where part of the adhesive remained on the tooth and part on the bracket. And the last type of failure(9.1%) occured at the adhesive-bracket interface.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.1
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• pp.75-81
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• 1985

The tensile and dielctric strength of the epoxied resin with bi-directional woven glass fibers with a laminate of two layers(G-10) are studied, and the test parameter is the angle between fiber orientation and the tensile axis. The obtained results may be summaried as follows: 1) when the angle between fiber orientation and tensile axis was varied from 0$^{\circ}$ to 45$^{\circ}$ the yield and fracture stresses have a tendency to decrease with increase in the angle. Especially, the decrease rates in the yield and fracture stresses are changed remarkably in the range of 0$^{\circ}$ to 15$^{\circ}$. 2) The fracture strain has showed the maximum value when the angle between fiber orientation and tensile axis is 45$^{\circ}$, and showed the rapid rate of change from 15$^{\circ}$ to 45$^{\circ}$. 3) For the sample with same angle between fiber orientation and tensile axis the maximum dielectric strength under compressive stress is decreased with increase in tensile stress, when the compressive stress is increased as a parameter of tensile stress. 4) When the angle between fiber orientation and tensile axis is 45$^{\circ}$, the dielectric strength showed the worst value, as the mechanical strength did.