• 한국구조물진단유지관리공학회 논문집
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• 제19권6호
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• pp.1-9
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• 2015

횡방향철근은 기둥의 소성힌지구간에 충분한 구속효과, 축방향철근의 좌굴방지와 연성거동을 확보하기 위해 적용된다. 기둥에서 사각형 후프 띠철근과 보강 띠철근의 조립 및 배근방법은 시공이 까다롭고 많은 횡방향철근량이 요구된다. 본 논문에서, 이러한 문제점들을 해결하기 위하여 장방형 단면과 플레어 기둥의 횡구속을 위한 장방형 후프 띠철근을 사용한 새로운 횡구속 방법이 제안되었다. 개발된 장방형 후프 띠철근 상세는 장방형 단면과 플레어 기둥의 시공성과 경제성을 향상시켜줄 수 있는 하나의 대안으로서 적용 가능한 것으로 판단된다. 본 연구의 최종목적은 철근콘크리트 교각의 시공성 향상을 위한 장방형 후프 띠철근 상세의 제시와 실험적 기초자료의 제공과 함께 하중단계별 성능 및 손상평가를 위한 정량적 수치와 경향을 제공하기 위한 것이며, 극한변위, 극한드리프트비율, 변위연성도, 응답수정계수, 등가점성감쇠비, 잔류변형지수, 유효강성 등의 주요 내진성능평가 변수들에 대한 분석결과를 나타내었다.

• 대한기계학회논문집A
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• 제40권12호
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• pp.1013-1019
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• 2016

CFRP는 탄소섬유를 기반으로 수지를 합침하여 제조된 복합소재로, 높은 비 강도와 경량성을 지녀 다양한 분야들에서 널리 사용되어지고 있다. 특히 일방향 탄소섬유는 적층 각도를 적용할 수 있으며 이때 적용된 적층 각도로 구성된 CFRP는 적층 각도가 없는 것보다 더 높은 강성을 가지고 있다. 본 논문에서는 적층 각도 변화에 따른 CFRP 소형 인장시험편의 크랙 전파와 파괴거동에 관한 것으로, 각 적층 각도에 따른 크랙 성장의 특성을 고찰한다. 적층 각도가 증가함에 따라 최대 응력 값이 작게 나타나고 크랙 전파가 더디게 나타나지만, 적층 각도 $60^{\circ}$를 기점으로 그 응력이 다시 증가되므로 서, 적층 각도에 따른 한계를 보이고 있다. 본 연구결과는 기계구조물의 CFRP사용에 있어 구조물내의 결함이 발생하였을 때의 피로파괴 가능성을 검증하는 자료로 사용될 수 있다고 사료된다.

• Coupled systems mechanics
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• 제8권4호
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• pp.299-313
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• 2019

The paper represents computer modeling of the deformed state of physically nonlinear transversally isotropic bodies with hole. In order to describe the anisotropy of the mechanical properties of transversally-isotropic materials a structurally phenomenological model has been used. This model allows representing the initial material in the form of the coupled isotropic materials: the basic material (binder) considered from the positions of continuum mechanics and the fiber material oriented along the anisotropy direction of the original material. It is assumed that the fibers perceive only the axial tensile-compression forces and are deformed together with the base material. To solve the problems of the theory of plasticity, simplified theories of small elastoplastic deformation have been used for a transversely-isotropic body, developed by B.E. Pobedrya. A simplified theory allows applying the theory of small elastoplastic deformations to solve specific applied problems, since in this case the fibrous medium is replaced by an equivalent transversely isotropic medium with effective mechanical parameters. The essence of simplification is that with simple stretching of composite in direction of the transversal isotropy axis and in direction perpendicular to it, plastic deformations do not arise. As a result, the intensity of stresses and deformations both along the principal axis of the transversal isotropy and along the perpendicular plane of isotropy is determined separately. The representation of the fibrous composite in the form of a homogeneous anisotropic material with effective mechanical parameters allows for a sufficiently accurate calculation of stresses and strains. The calculation is carried out under different loading conditions, keeping in mind that both sizes characterizing the fibrous material fiber thickness and the gap between the fibers-are several orders smaller than the radius of the hole. Based on the simplified theory and the finite element method, a computer model of nonlinear deformation of fibrous composites is constructed. For carrying out computational experiments, a specialized software package was developed. The effect of hole configuration on the distribution of deformation and stress fields in the vicinity of concentrators was investigated.

• Computers and Concrete
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• 제26권6호
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• pp.547-563
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• 2020

In this paper, the influence of axial compression ratio on the mechanical properties of new type joints of side span of rectangular concrete-filled steel tubular column-H-type steel beam is studied. Two new types of side-span joints of rectangular concrete-filled steel tubular column-H-type steel beam are designed and quasi-static tests of five new type joints with 1:2 scale reduction ratios are performed. The axial compression ratio of joint JD1 is 0.3, 0.4 and 0.5, and the axial compression ratio of joint JD2 is 0.3 and 0.5. In the joint test, different axial forces were applied to the top of the column according to different axial compression ratios, and low-cyclic reciprocating load was applied on the beam. The stress and strain distribution, beam and column deformation, limit state, failure process, failure mechanism, stiffness degradation, ductile deformation and energy dissipation capacity of the joint were measured and analyzed. The results show that: with the increase of axial compression ratio, the ultimate bearing capacity of the joint decreases slightly, the plastic deformation decreases, and the stiffness and ductility decrease. According to the energy dissipation curve of the specimen, the equivalent damping coefficient also increases with the increase of axial compression ratio in a certain range, indicating that the increase of axial compression ratio can improve the seismic performance of the joint to a certain extent. The finite element method is used to simulate the joint test, and the test results are in good agreement with the simulation results.

• Journal of Pharmaceutical Investigation
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• 제37권3호
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• pp.137-148
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• 2007

Using a strain-controlled rheometer [Rheometrics Dynamic Analyzer (RDA II)], the steady shear flow properties of a semi-solid ointment base (vaseline) have been measured over a wide range of shear rates at temperature range of $25{\sim}60^{\circ}C$. In this article, the steady shear flow properties (shear stress, steady shear viscosity and yield stress) were reported from the experimentally obtained data and the effects of shear rate as well as temperature on these properties were discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters (yield stress, consistency index and flow behavior index). Main findings obtained from this study can be summarized as follows : (1) At temperature range lower than $40^{\circ}C$, vaseline is regarded as a viscoplastic material having a finite magnitude of yield stress and its flow behavior beyond a yield stress shows a shear-thinning (or pseudo-plastic) feature, indicating a decrease in steady shear viscosity as an increase in shear rate. At this temperature range, the flow curve of vaseline has two inflection points and the first inflection point occurring at relatively lower shear rate corresponds to a static yield stress. The static yield stress of vaseline is decreased with increasing temperature and takes place at a lower shear rate, due to a progressive breakdown of three dimensional network structure. (2) At temperature range higher than $45^{\circ}C$, vaseline becomes a viscous liquid with no yield stress and its flow character exhibits a Newtonian behavior, demonstrating a constant steady shear viscosity regardless of an increase in shear rate. With increasing temperature, vaseline begins to show a Newtonian behavior at a lower shear rate range, indicating that the microcrystalline structure is completely destroyed due to a synergic effect of high temperature and shear deformation. (3) Over a whole range of temperatures tested, the Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable and have an almostly equivalent ability to quantitatively describe the steady shear flow behavior of vaseline, whereas the Bingham, Casson,and Vocadlo models do not give a good ability.

• Nuclear Engineering and Technology
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• 제21권2호
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• pp.111-122
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• 1989

고온 수증기(1323 K)분위기에서 산화시킨 지르칼로이-4 피복관으로, 구리 맨드렐 팽창실험(Copper Mandrel Expension Test)을 변형률(Strain Rate)이 $3.0\times10^{-5}$/sec일때 673-1173 K 온도 범위에서 수행하였다. 본 연구에서, 산화매개변수(Ki)는 시간(t)의 제곱근에 비례하고 $(Ki=\delta_{kit}\frac{1}{2}$), 비례상수($\delta_{ki}$)는 무게증가(Weight Gain), Zr02의 두께, $\alpha$(0) 층에 대하여 각각 0.281, 2.82, 2.313을 사용하였다. 지르칼로이-4의 고온(873-1073 K) 소성변형에 의한 활성화 에너지는 Zr02가 높은 강도를 갖기 때문에 산화 시간이 5분에서 60분으로 증가함에 따라 251 KJ/mol에서 323KJ/mo1로 증가하였다. 산화막 두께, K와 항복 응력의 관계는 ($\sigma/C)^n=K^m$exp (Q/RT)인 관계식을 얻었다. 여기서 n은 6.9, m은 5.7, 그리고 Q가 251, 258, 316, 323 KJ/mo1에 대해 C는 0.155, 0.138, 0.051, 0.046MPa이다.