• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.197-200
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• 2001

A manufacturing process of composite pressure vessel was studied. The vessel was fabricated using the filament winding process. It is utilized as a container of high pressure Helium gas which propels a rocket fuel and an oxidizer. The layup patterns were determined based on the lamination theory. 3-axis controlled filament winding machine was developed to realize the patterns. The vessel was successfully fabricated using the developed machine. And the hydraulic pressure test was performed to measure an applied pressure-strain relations on the composite vessel.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.159-165
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• 2006

Many rubber products are used in industrial products such as various hoses, rubber belts and oil seals etc. Especially, more then 200 rubber parts are used in the automobile, but design technology of these is largely dependent on Held experiences. These methods brought about too much time and cost in the developing procedures. However, with the help of recent rapid development of non-liner computer analysis, we can develop new sound products at low cost. Therefore in this study, optimizations of design variables such as location and number of gate in order to develop CLIP rubber product made of EPDM were performed by CAE in which Cross-WLF equations are adopted. The validity of proposed variables is evaluated by comparison with real forming results.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.648-651
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• 2009

탄소섬유강화플라스틱(CFRP:Carbon Fiber Reinforced Plastic)용기의 외부에 화재가 발생할 경우 함침된 수지(Resin)가 탄화되면서 자체 강도가 약화되고 충전된 가스가 외부 온도 상승에 따라 압력 상승이 발생하여 용기의 폭발로 이어지는 사고가 발생할 개연성이 높다. 화염 노출조건에서 복합재료 용기의 폭발을 방지하기 위하여 용기용 밸브에 내장된 온도감응식 압력안전장치(TPRD:Thermally activated Pressure Relief Device) 작동 성능을 검증하기 위한 방법으로 화염실험(Bonfire test)를 실시하고 있으나, 개방 공간에서 실시되는 이 실험은 표면 온도 변화가 매우 크게 발생하여 실험에 대한 재현성(Reproducibility)에 의문이 제기되고 있다. 따라서, 표면 온도를 일정하게 유지하기 위한 실험 방법의 개선이 필요하다. 본 연구에서는 경유+heptane을 이용한 전체 화염에 노출되는 경우와, 천연가스를 이용한 단일화염에 노출되는 경우의 실험 결과 비교를 통하여 화염 노출 표면 온도를 일정하게 유지하기 위한 가열 방법의 타당성을 검토하였다. 또한, 복합재료 라이너(Liner)의 온도 변화 비교를 통하여 집중화염 노출 조건에서 열전달 특성을 알아보았다.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.73-81
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• 2010

The paper presents the application of FE simulations of NATM tunnel using different constitutive models. The results from a series of two dimensional plane strain finite element analyses of medium-liner interaction for NATM are presented. Four types of constitutive models are considered, namely, linear elastic, elasto-plastic Mohr-Coulomb, Hardening-Soil, Soft-Soil model. The design for tunnels requires a proper estimate of surface settlement and lining forces. It is shown that the advanced constitutive model gives better predictions for both ground movement and structural forces.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1494-1501
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• 2006

Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600$^{\circ}C$. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400$^{\circ}C$, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400$^{\circ}C$ while stress-strain curve is changed at 500$^{\circ}C$ as the strain rate is changed. Creep tests were conducted at 250$^{\circ}C$ and 500$^{\circ}C$ and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.403-414
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• 1994

Nonlinear analysis of RC containment structure under thermal load and pressure is presented to trace the behaviour after an assumed LOCA. The temperature distribution varying with time through the wall thickness is determined by transient finite element analysis with the two time level scheme in time domain. The layered shell finite elements are used to represent the containment structures in nuclear power plants. Both geometric and material nonlinearities are taken into account in the finite element formulation. The constitutive relation of concrete is modeled according to Drucker-Prager yield criteria in compression. Tension stiffening model is used to represent the tensile behaviour of concrete including bond effect. The reinforcing bars are modeled by smeared layer at the location of reinforcements accounting elasto-plastic axial behaviors. The steel liner model under Von Mises yield criteria is adopted to represent elastic-perfect plastic behaviour. Geometric nonlinearity is formulated to consider the large displacement effect. Thermal stress components are determined by the initial strain concept during each time step. The temperature differential between any two consecutive time steps is considered as a load incremental. The numerical results from this study reveal that nonlinear temperature gradient based on transient thermal analysis will produces excessive large displacement. Nonlinear behavior of containment structures up to ultimate stage can be traced reallistically. The present study allows more realistic analysis of concrete containment structures in nuclear power plants.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.43-71
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• 1999

This research is an experimental work of developing a construction material using municipal wastewater sludge as liner and cover materials for waste disposal landfill. Weathered granite soil and flyash, produced as a by-product in the power plant, were used as the primary additives to improve geotechnical engineering properties of sludge. For secondary additives, bentonite and cement were mixed with sludge to decrease the permeability and to increase the shear strength, respectively. Various laboratory test required to evaluate the design criteria for liner and cover materials, were carried out by changing the mixing ratio of sludge with the additives. Basic soil properties such as specific gravity, grain size distribution, liquid and plastic limits were measured to analyze their effects on permeability, compaction, compressibility and shear strength properties of mixtures. Laboratory compaction tests were conducted to find the maximum dry densities and the optimum moisture contents of mixtures, and their effectiveness of compaction in field was consequently evaluated. Permeability tests of variable heads with compacted samples, and the stress-controlled consolidation tests with measuring permeabilities of samples during consolidation process were performed to obtain permeability, and to find the compressibility as well as consolidational coefficients of mixtures, respectively. To evaluate the long term stability of sludges, creep tests were also conducted in parallel with permeability tests of variable heads. On the other hand, for the compacted sludge decomposed for a month, permeability tests were carried out to investigate the effect of decomposition of organic matters in sludges on its permeability. Direct shear tests were performed to evaluate the shear strength parameters of mixed sludge with weathered granite, flyash and bentonite. For the mixture of sludge with cement, unconfined compression tests were carried out to find their strength with varying mixing ratio and curing time. On the other hand, CBR tests for compacted specimen were also conducted to evaluate the trafficability of mixtures. Various test results with mixtures were assessed to evaluate whether their properties meet the requirements as liner and cover materials in waste disposal landfill.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.205-216
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• 1994

The purpose of this study is to evaluate of apical plug materials for the contral of extrusion and sealing ability of high-temperature thermoplasticized gutta-percha in plastic root canal blocks. Seventy seven plastic blocks with canal preformed were instrumented with # 50K file 1 mm beyond apical foramen. Blocks were randomly divided into 5 groups of 15 blocks each. Group 1 was filled by high-temperature thermoplasticized gutta-percha only. The another 4 groups were placed with apical plug materials each other and then remaining space was back filled with high temperature thermoplasticized gutta-percha Apical plug materials were used as follows; Group 2: Thermoplasticized gutta-percha (Thermoplasticized gutta-percha group) Group 3 :. Calcium hydroxide powder (Calcium hydroxide group) Group 4 : Silver point (Silver point group) Group 5 : Gutta-percha cone softened by chloroform (Gutta-percha cone group) All the blocks were stored in 100 % relative humidor at room temperature for 14 days. Filling material extruded was removed carefully and then weighed in analytic balance. Each block was placed in centrifuge tube filled with India ink, and then centrifuged for 20 minutes at 3,000 rpm. Apical leakage was measured from the apical foramen to the most coronal level of dye leakage in millimeter by two examiners under a stereoscope. The data were analysed statistically by Student's t-test The obtained results were as follows; 1. The amounts of material extruded through the foramen decreased in all of groups used apical plug materials (P<0.01). 2. Silver point group and gutta-percha cone group were similar linear leakage to high-temperature thermoplasticised gutta-percha technique only (P>0..5). 3. Calcium hydroxide group and thermoplasticized gutta-percha group showed more liner leakage than high-temperature thermoplasticized gutta-percha only (P<0.01, P<0.05). 4. High-temperature thermoplasticized gutta-percha technique with silver point and gutta-percha cone as apical plugs showed less linear leakage and less extrusion of filling material.

• Journal of the Korean Society of Food Culture
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• v.32 no.4
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• pp.303-310
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• 2017

Kimchi cabbage is in demand all year, but there is an unbalance in its supply and demand due to climate reasons, requiring practical methods for extending storage without high cost. Therefore, this study aimed to assess available storage methods. 'Choongwang' Kimchi cabbages cultivated in Pyeongchang, Gangwon-do were on June 14 harvested and packed in plastic boxes. Control group was treated by loading four to five heads. Moisturized paper was applied as a liner inside the box to prevent dehumidification and damage to the cut root parts, and a small loading amount (three heads) was applied for better air circulation. Weight loss rates after 12 weeks of storage were 13.83% in the control group, 12.57% in the first group, and 13.38% in the second group. Trimming loss rates after 9 weeks of storage were 14.96% in the control group, 12.29% in the first group, and 12.55% in the second group. As a result of the sensory test, the control group lost its marketability after 6 weeks of storage, while the second group maintained it until 9 weeks and the first group maintained it until 12 weeks and scored higher than 6 points. Therefore, the tested methods were effective for extending the freshness of Kimchi.

• Composites Research
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• v.23 no.6
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• pp.7-13
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• 2010

Type3 cylinder is a composite pressure vessel fully over-wrapped with carbon/epoxy composite layers over an aluminum liner, which is the most ideal and safe high pressure gas container for CNG vehicles due to the lightweight and the leakage-before-burst characteristics. During service in CNG vehicle, if a fiber cut damage occurs in outer composite layers, it can degrade structural performance, reducing cycling life from the original design life. In this study, finite element modeling and analysis technique for the composite cylinder with fiber-cut crack damage is presented. Because FE analysis of type3 cylinder is path dependant due to plastic deformation of aluminum liner in autofrettage process, method to introduce a crack into FE model affect analysis result. A crack should be introduced after autofrettage in analysis step considering real circumstances where crack occurs during usage in service. For realistic simulation of this situation, FE modeling and analysis technique introducing a crack in the middle of analysis step is presented and the results are compared with usual FE analysis which has initial crack in the model from the beginning of analysis. Proposed analysis technique can be used effectively in the evaluation of influence of damage on composite layers of type3 cylinder and establish inspection criteria of composite cylinder in service.