• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2004년도 학술대회지
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• pp.33-38
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• 2004

This study was performed to know watertightness and reduction effect and crack occurred by hydration heat, restraint of multiplication of hydration heat, through mechanical test, strength test and crack control test using fluosilicate salt based inorganic compound made from by-product during phosphoric acid manufacturing process. Mix proportions for experiment were modulated at 0.45 of water to cement ratio and $0.5-2.0\%$ of adding ratio of fluosilicate salt based inorganic compound. Evaluation for watertightness of concrete was carried out permeability, absorption test and porosity analysis. Effect of crack reduction was evaluated by length, drying shrinkage as well as stress change of hardened concrete at unrestraint/restraint state and also elucidated crack pattern on the concrete surface. It is ascertained that characteristics of crack resistance and watertightness for concrete was improved by an adequate addition of fluosilicate salt based inorganic compound.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1939-1943
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• 2008

Deformation of a mold is measured and analyzed in alignment and curing processes of UV-Imprint Lithography. We are focused on mold deformation caused by a UV resin, which is laminated between a mold and a target glass-panel. The UV resin is viscous in case of liquid state, and the resin will be solidified when being exposed by the ultra-violet light. The viscosity of the resin causes shear force on the mold during the alignment process. Moreover, the shrinkage during phase change from liquid to solid may cause residual stress on the mold. The experiments for measuring temperature and strain are made during alignment and curing process. Strain-gages and thermocouples are used for measuring the strain and variation of temperature on several points of the mold, respectively. The deformation of mold is also simulated and analyzed. The simulation results are compared with the experiments. Finally, sources of alignment errors in large area UV-nanoimprint lithography are discussed.

• 한국기계가공학회지
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• 제17권4호
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• pp.9-16
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• 2018

Recently, the demand for eco-friendly parts has increased to reduce materials and parts that use fossil fuels. This has exacerbated the increase of energy prices and the enforcement of regulations by environmental agencies. Currently, polylactic acid (PLA) is a solution, as a common and eco-friendly material. PLA is a biodegradable material that can replace traditional petrochemical polymers. PLA has great advantages since it is resistant to cracking and shrinkage. When it is manufactured, there are few harmful byproducts. Improvement in the brittleness characteristics is another important task to be monitored throughout the production of industrial parts. Improvement in the brittleness property of products lowers the tensile strength and tensile elasticity modulus of the parts. This study focused on the mechanical properties of 3D-printed PLA parts. Tensile tests are performed while varying the infill print parameters to evaluate the applicability of PLA in several industrial areas.

• 한국항공우주학회지
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• 제39권8호
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• pp.711-718
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• 2011

본 논문에서는 열화학적 분해 및 열기계학적 변형이 고려된 구성 방정식을 사용하여 다공성 탄소/페놀릭 복합재료의 열탄성 거동을 예측하였다. 다공성 복합재료의 온도 의존성 및 열화학적 분해 과정에서의 기공도, 분해 가스에 의한 기공 압력, 재료의 수축을 고려하였다. 기공도와 기공 압력이 고려된 대표 체적 요소 모델의 유한요소 해석을 통해 산출된 거시적 기공 탄성 계수를 구성 방정식에 적용하였다. 간단한 수치 실험을 통해 기공탄성 계수가 다공성 재료의 열탄성 거동에 미치는 영향을 분석하였으며, 재료 내부에 형성된 기공과 기공 압력에 의한 응력 구배 및 변형을 확인하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.183-194
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• 2002

A general procedure to evaluate the sensitivity of design variables to stresses and strains in PSC flexural members is proposed. To accomplish the purpose of this study, long-term losses including creep, shrinkage, and PS steel relaxation are formulated based on the equilibrium states of the deformed sectional geometry. Thereby, the formulation follows the basic steps which consider the fundamental formulas adopted by CEB-FIP, ACI, and KCI rather than the age adjusted effective modulus concept. Twenty-one design variable including the material and geometrical properties of concrete, nonprestressing steel and prestressing steel, and the geometry of the cross section are considered in the sensitivity analysis. The gradients of the stresses and strains needed for the sensitivity assessment are calculated in a closed format. The derived formulation is applied to the T-type section PSC beam with prestressing and nonprestressing steels for the sensitivity analysis. The analytically calculated sensitivity results are compared with those numerically calculated to ensure the validity of the proposed procedure.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.995-1000
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• 2000

Segmentally erected prestressed concrete box girder bridges have been widely used in Korean high speed railway. Segmental erection has been accomplished along the longitudinal direction and across the depth of cross section. The cross section is similar to a composite cross section, composed of old and new segments. Because these segments have different time-dependent creep and shrinkage properties, a stress redistribution takes place during the construction period. It is the main objective in this research to investigate this behavior. An actual bridge was instrumented with 96 vibrating wire embedded type strain gauges, 6 electronic type steel strain gauges, and 75 thermocouples. Two span continuous high speed railway bridge was selected. Two points of importance, such as the midpoint of the first span and the point of interior support, along the span of the girder were chosen to monitor the time dependent behaviors for an extended period of time. The data collection was starting just after concrete girder were cast and is still going on. According to the measured results, the strain distributions across the depth of the section at midspan and interior support were not continuous and the important redistribution of stresses takes place. Thus, rational design of prestressed concrete composite box girder bridges need.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.813-816
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• 2008

본 연구는 방곰팡이제의 혼입율 변화에 따른 방곰팡이 모르터의 물리적 특성 및 곰팡이 생성억제 효과에 대하여 검토한 것으로써, 그 결과를 요약하면 다음과 같다. 방곰팡이제를 혼입한 모르터의 플로우, 압축강도, 건조수축 길이변화는 방곰팡이제 혼입율에 관계없이 Plain과 유사한 값으로 나타나, 방곰팡이제의 혼입이 모르터의 물리적 특성에는 큰 영향을 미치지 않는 것으로 나타났다. 방곰팡이제를 혼입한 모르터는 Plain에 비해 매우 적은 양을 혼입하였음에도 높은 곰팡이 저항성을 나타내었고, 그 혼입량이 증가됨에 따라 곰팡이 저항성 또한 크게 증가하였다. 배합비 별로는 1:4 배합의 모르터가 1:2 배합 모르터보다 높은 곰팡이 저항성을 보였다.

• 전기학회논문지
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• 제64권8호
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• pp.1154-1160
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• 2015

This paper describes the thermal characteristics of underground power cable system terminations according to the change of ambient temperature as well as operating temperature. Recently, the failure has been gradually increasing in outdoor termination during winter season because the power demand was increased by electricity heating system. The power demand and outdoor temperature is difference between day time and night time. The temperature difference has an influence on conductor extension and shrinkage due to conductor force as well as thermal mechanical characteristics. These phenomena have daily repeated during heating and cooling period of conductors. In these cases, the insulation of outdoor terminations might be degraded by the reduced interface pressure surrounding stress relief cone. Therefore, in this paper, the thermal characteristics are variously analysed by simulation considering power demand and ambient temperature condition during winter season at epoxy type termination as well as slip-on type termination

• Steel and Composite Structures
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• 제13권3호
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• pp.277-293
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• 2012

The interaction between steel tube and concrete core is the key design considerations for concrete-filled steel tube columns. In a concrete-filled steel tube (CFST) column, the steel tube provides confinement to the concrete core which permits the composite action among the steel tube and the concrete. Due to construction faults and plastic shrinkage of concrete, the debonding separation at the steel-concrete interface weakens the confinement effect, and hence affects the behaviour and bearing capacity of the composite member. This study investigates the axial loading behavior of the concrete filled circular steel tube columns with debonding separation. A three-dimensional nonlinear finite element model of CFST composite columns with introduced debonding gap was developed. The results from the finite element analysis captured successfully the experimental behaviours. The calibrated finite element models were then utilized to assess the influence of concrete strength, steel yield stress and the steel-concrete ratio on the debonding behaviour. The findings indicate a likely significant drop in the load carrying capacity with the increase of the size of the debonding gap. A design formula is proposed to reduce the load carrying capacity with the presence of debonding separation.

• 한국분말재료학회지
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• 제17권1호
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• pp.1-6
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• 2010

In this study, a convergent heat treatment was performed in certain temperature regions in order to control the microstructures of Nd-rich phases and to reduce thermal stress on grain boundaries which could be caused during expansion and shrinkage of Nd-rich and $Nd_2Fe_{14}B$ phases. The difference of thermal expansion coefficient between $Nd_2Fe_{14}B$ and Nd-rich phases is the mechanism for convergent heat treatment. The Nd-rich phases which were located in junctions could penetrate into the grain boundaries between $Nd_2Fe_{14}B$ phases due to the difference of thermal expansion coefficient. Through the convergent heat treatment, the microcracks that were observed in cyclic heat treatment were not observed and coercivity was increased to 34.05 kOe at 8 cycles.