• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.521-529
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• 2002

A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

• 한국전기화학회:학술대회논문집
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• 2002.07a
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• pp.251-258
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• 2002

[ $Ni-10wt.\%Cr$ ] green sheet를 불활성분위기로 $900^{\circ}C$까지 승온시킨 다음 부분산화$(P_{H2}/P_{H2O}=10^{-2})$후 $1100^{\circ}C$에서 3시간 환원처리를 시키는 소결공정으로 Ni-Cr 고용체 기지 주변에 작은 $Cr_2O_3$ 알갱이가 고르게 분포하는 anode(Anode Sintered in Partial oxidation - Reduction atmosphere; ASPR)를 제조하였으며, creep 변형률이 $2.8\%$로서 미세구조에 따른 creep 특성의 비교를 위해 기존의 환원분위기에서만 소결시킨 anode(Anode Sintered in Reduction atmosphere only; ASR)의 $11\%$보다 우수한 creep 저항성을 나타내었다. $Cr_2O_3$ 알갱이가 분산된 미세구조른 부분산화 시 Cr과 Ni의 산화속도 및 확산속도의 차이로 인해 형성되는 것으로 사료되며, creep 전${\cdot}$후 ASPR 시편의 SEM 및 기공률 분석결과 매우 안정적으로 그 형상 및 구조를 유지하고 있음을 확인할 수 있었다. 또한 ASPR 시편의 전기전도도는 약 $15\times10^6\;S/m$로서 기존 ASR 시편의 전기전도도와 유사함을 알 수 있었다.

• Journal of Welding and Joining
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• v.9 no.3
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• pp.10-17
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• 1991

용접구조물에서 용접이음부가 차지하는 비율은 매우 작은 경우가 많지만 용접이음부에는 각종 초기결함(이들 결함으로부터 진전하는 피로 균열, 환경에 의한 균열등을 포함) 및 용접 초기의 부정형을 비롯해서 형상적 불연속 등에서 유기되는 국부적인 응력, 변형률의 집중, 잔류응력, 구속응력, 용접금속이 갖는 숙명적인 야금적 특성의 불균일, bond부 및 HAZ부에서의 용접열 싸이클에 의한 재질의 국부적 강도저하등 용접부의 강도를 저하시키는 인자들이 복합되기 쉽고, 용접구조물 전체의 내파괴 건전성평가에서 용접부가 파괴 강도는 매우 중요하다. 용접구조물의 설계, 시공의 목적은 소요성능의 확보에 있고 구조물이 사용중에 성능손실이나 불안정 파괴가 발생하지 않도록 하는 것이 주요요건이 될 것이다. 현재의 제강기술수준에서 볼 때 모재의 강 도보다 오히려 용접부의 강도 특히 피로강도 및 파괴 인성을 적절하고 합리적으로 평가하는 것이 매우 중요하다고 해도 과언이 아닐 것이다. 용접부의 강도를 평가하는데 있어서 용접부에 발 생하는 용접결함에 대한 평가는 매우 중요하며 이들 결함에 대한 허용결함한계를 평가하여 보수 여부 및 용접구조물의 신뢰성을 평가 할 필요가 있다.

• Korean Journal of Materials Research
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• v.7 no.6
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• pp.517-521
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• 1997

고분해능 전자현미경과 컴퓨터 이미지 시뮬레이션이 La이 첨가되고 또한 첨가되지 않은 Pb(Mg/ sub 1/3/Nb$_{2}$3/)O$_{3}$고용체의 미세구조를 연구하기 위해서 사용되었다. 불규칙격자 영역의 격자 이미지는 정방정 형태와 유사 육방정 형태를 각각 보였다. 규칙격자 영역에서 Mg과 Nb의 비화학양론적인 규칙격자 구조 현상이 <111>방향에 따라 관찰되었다. 실험 격자 이미지와 컴퓨터 시뮬레이션 이미지의 비교로부터, 규칙격자 구조를 가지는 영역의 장거리 규칙도는 0.2-0.7의 값을 가지고 있었고, 또한 규칙격자는 (NH$_{4}$)$_{3}$FeF$_{6}$결정구조를 가지고 있었다. 작은 값의 장거리 규칙도를 가지는 규칙격자를 가지는 영역에서, 변형률 파형이 관찰되지 않았다. 이것은 대부분 두 양이온이 그들의 위치에 있기 때문에, 원자 변위가 없었기 때문이다.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.571-579
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• 2016

RS-LMC (Rapid Setting Latex Modified Concrete) has been widely used as repair material for bridge deck overlay or rehabilitation, because the overlaid pavement could be opened to the traffic after 3 hours of curing. Although the field performance of RS-LMC generally indicates that it has an excellent bonding to the substrate and shows a long term performance, the crack by vibration of vehicles have been happened on the overlay of bridges in technical reports. In this study, experimental research was carried out to evaluate the vibration properties of RS-LMC overlays by using P.S.T (Pavement Shaking Table). Total 12 specimens were tested and the variables are Latex-cement ratio (L/C) and amplitude of vibration. The result shows that the number of cracks and the total length of cracks are reduced as the increase of Latex-cement ratio (L/C) until 15%. And the crack occurs at a very small strain than the proposed values by Walter, D, G and design codes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.1
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• pp.9-15
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• 2005

Dredged soil from sea has much higher water content than liquid limit of clay and even if small loads apply, it will suffer a great settlement. Therefore it is very difficult to perform a consolidation test with general consolidation apparatus because of high water content. In this study Rowe cell apparatus consolidation tests have been performed with 5 slurry clays of a water content of 100%, 110%, 120%, 133%, and 150%. From the test results the consolidation characteristics such as compression index, secondary compression index, consolidation coefficient, and strain have been investigated with a variation of water content of dredged soil. The equations to get consolidation constants such as a compression index, a coefficient of consolidation, and strain have been proposed with the field water content.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.87-94
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• 2009

Volume of concrete slab changes by variations of temperature and moisture after its placement. Shrinkage due to evaporation causes tensile stress in the slab when contraction of the slab is restrained by its self weight, friction with subbase, and etc. Actual tensile stress caused by the shrinkage was less than theoretically predicted stress according to previous studies. It was the stress reduction due to visco-elastic property of the early-age concrete slab partially restrained. In this study, strains of restrained circumferential, unrestrained circumferential, and unrestrained square pillar concrete specimens were measured to investigate stress reduction of the specimens with age of concrete. Elastic modulus of the concrete was measured at the age of 1, 3, 7, 14, 28 days and penetration test was performed. The stress reduction was calculated by input the test results into theoretical equations suggested by previous researchers. The stress reduction of the restrained concrete specimens will be applied to design of concrete pavements based on results of the study.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.50-60
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• 2023

Ball Grid Array (BGA) is a widely used package type due to its high pin density and good heat dissipation. In BGA, solder balls play an important role in electrically connecting the package to the PCB. Therefore, understanding the inelastic deformation of solder balls under various mechanical loads is essential for the robust design of semiconductor packages. In this study, the geometrical effect on the inelastic deformation and fracture of solder balls were analyzed by finite element analysis. The results showed that fracture occurred in both tilted and hourglass shapes under shear loading, and no fracture occurred in all cases under compressive loading. However, when bending was applied, only the tilted shape failed. When shear and bending loads were combined with compression, the stress triaxiality was maintained at a value less than zero and failure was suppressed. Furthermore, a comparison using the Lagrangian-Green strain tensor of the critical element showed that even under the same loading conditions, there was a significant difference in deformation depending on the shape of the solder ball.

• Journal of Chest Surgery
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• v.31 no.5
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• pp.456-465
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• 1998

Cardiopulmonary bypass(CPB) in children is associated with the accumulation of body water after cardiac operation, as a consequence of an inflammatory capillary leak. Following work by Elliott in 1991, modified ultrafiltration(MUF) was introduced after bypass as a means of hemoconcentrating patients and a potential way of removing water from the tissues. We have carried out a prospective randomized study of 20 children undergoing open heart surgery, comparing MUF with nonfiltered controls. MUF was carried out for a mean of 18.9 minutes after completion of CPB to a hematocrit of 37.1%(mean). The mean water volulme removed by the ultrafiltration was 38.4 ml/kg and the mean blood volume retransfused from the oxygenator during the ultrafiltration was 32.1 ml/kg. Fluid balance, hemodynamics, hematocrit, osmolarity and dosage of drug treatment were recorded for 4∼12 hours postoperatively. The results were analyzed using Student t-test and ANOVA, comparing controls(n=10) to MUF(n=10). Blood loss(ml/kg/24hr) was 14.5(mean) in MUF versus 13.7 in controls; blood transfused(ml/kg/24hr) 6.6 in MUF versus 15.2 in controls; plasma transfused(ml/kg/24hr) 65.7 in MUF versus 59.6 in controls. There was rise in arterial blood pressure and hematocrit during MUF. Percent rise of systolic blood pressure was 28.8% in MUF versus 18.7% in controls(p=0.366); percent rise of diastolic blood pressure was 28.8% in MUF versus 8.5% in controls(p=0.135); and percent rise of mean blood pressure was 36.2% in MUF versus 8.2% in controls (p=0.086). Percent rise of hematocrit was 40.0% in MUF versus 23.5% in controls(p=0.002). There was no significant difference in the inotropic requirement and the postoperative serum osmolarity between two groups. The number of days on the ventilator, the duration of stay in the intensive care unit, and the postoperative hospital stay were not significantly different between the two groups.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.1-10
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• 2014

This paper presents the results of a field pilot test about deformation of water supply pipelines due to freezing temperature. There is a difference between for frost heaving load to act on the water supply pipelines. If the Marston-Spangler theory is only considered for the frost heaving load to act on the water supply pipeline, it is likely to deviate from the safety of the water supply pipeline, strains of the water supply pipeline show a tendency of smaller value than the value of numerical analysis.