• Composites Research
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• 제29권4호
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• pp.173-178
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• 2016

Graphene oxide (GO) was concurrently reduced and functionalized using long alkyl chain dodecyl amine (DA). The DA functionalized GO (DA-G) was assumed to disperse homogenously in linear low density polyethylene (LLDPE). Subsequently, DA-G was used to fabricate DA-G/LLDPE composites by melt mixing technique. Fourier transform infrared spectra analysis was performed to ascertain the simultaneous reduction and functionlization of GO. Field emission scanning electron microscopy analysis was performed to ensure the homogenous distribution and dispersion of DA-G in LLDPE matrix. The enhanced storage modulus value of the composites validates the homogenous dispersion of DA-G and its good interfacial interaction with LLDPE matrix. An increased in tensile strength value by ~ 64% also confirms the generation of good interface between the two constituents, through which efficient load transfer is possible. However, no significant improvement in glass transition temperature was observed. This simple technique of fabricating LLDPE composites following industrially viable melt mixing procedure could be realizable to developed mechanically strong graphene based LLDPE composites for future applications.

• Structural Engineering and Mechanics
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• 제63권5호
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• pp.585-595
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• 2017

This study aimed to presents a simple analytical approach to investigate the thermal buckling behavior of thick functionally graded sandwich by employing both the sinusoidal shear deformation theory and stress function. The material properties of the sandwich plate faces are continuously varied within the plate thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises across the thickness direction. Numerical examples are presented to prove the effect of power law index, loading type and functionally graded layers thickness on the thermal buckling response of thick functionally graded sandwich.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.401-415
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• 2017

A new higher shear deformation theory (HSDT) is presented for the thermal buckling behavior of functionally graded (FG) sandwich plates. It uses only four unknowns, which is even less than the first shear deformation theory (FSDT) and the conventional HSDTs. The theory considers a hyperbolic variation of transverse shear stress, respects the traction free boundary conditions and contrary to the conventional HSDTs, the present one presents a new displacement field which includes undetermined integral terms. Material characteristics and thermal expansion coefficient of the sandwich plate faces are considered to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are supposed as uniform, linear and non-linear temperature rises within the thickness direction. An energy based variational principle is used to derive the governing equations as an eigenvalue problem. The validation of the present work is carried out with the available results in the literature. Numerical results are presented to demonstrate the influences of variations of volume fraction index, length-thickness ratio, loading type and functionally graded layers thickness on nondimensional thermal buckling loads.

• 지질공학
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• 제7권3호
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• pp.173-189
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• 1997

유성온천장을 중심으로 불측 인접지역에서의 온천개발 가능성을 평가하기 위하여 주변의 지질구조와 지온분포에 관한 연구를 시도하였다. 연구지역 주변지역에서 온천수 형셩과 관련된 요인은 단층과 암맥이며 물탐자료와 지온측정자료 해석결과는 이를 어느 정도 뒷받침하고 있다. EW 예상 단층선은 본 지역의 북부를 스쳐 지나가며 N40$^{\circ}$W 예상 단층선은 본 지역의 서측에서 EW의 예상 단층과 교차한다. 이러한 예상 단측의 위지는 선구조선의 분석, 물탐자료 및 자료 및 지온측정의 결과에서 잘 반영된다. 연구지역 내에는 3개조의 암맥이 관입되어 있는 것으로 판단된다. 지온측정 결과 지온 이상대와 암맥의 위치는 서로 일치하며, 지하 1m와 0.5m 사이의 온도차는 3$^{\circ}C$ 이상이다. 지하 1m와 0.5m 사이의 온도차는 2.5$^{\circ}C$ 이상의 지온 이상대는 연구지역 내에서 N80$^{\circ}$W의 방향으로 형성되어 있다. 암맥의 경사는 암맥의 직선적인 분포나 노두에서의 조사결과로부터 거의 수직인 것으로 판단된다. 온도 이상대 분포와 암맥의 위치로부터 연구지역 내에서 온천수 부존 가능 위치로 세곳을 들을 수 있으며 이들 지점에서 4$0^{\circ}C$ 이상의 온천수를 확보할 수 있는 깊이는 170~200m 내외로 추정된다.

• 한국토양비료학회지
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• 제15권4호
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• pp.221-225
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• 1982

작물시험장(作物試驗場) 춘천출장소(春川出場所) 냉수시험답(冷水試驗畓)에서 최고분얼기(最高分蘖期)부터 출수기(出穗期)까지 냉수(冷水)($16^{\circ}C$) 유입구(流人口)로부터 거리별(距離別) 수온 및 지온의 변화양상(變化樣相)을 측정(測定)하고 이에 따른 수도생육(水稻生育) 및 수량변화 관계를 농백(農白)과 밀양(密陽)23호(號)에 대하여 조사(調査)하였다. 관개수(灌漑水)의 이동거리(移動距離)가 증가됨에 따라 수온은 급격(急激)히 상승(上昇)되어 $21^{\circ}C$에 접근(接近)하는 양상(樣相)을 보였으나 지온은 직선적(直線的)으로 완만(緩慢)하게 증가되어 수온보다 $1{\sim}2^{\circ}C$ 낮은 수준(水準)으로 유지(維持)되었다. 수온과 토양온도가 낮으면 간장(稈長) 및 이삭의 추출도(抽出度)가 줄어들고 출수(出穗)가 지연(遲延)되며 수량구성요소는 주당수수, 천입중(千粒重) 및 임실률 떨어져 감수되는 것으로 나타났다. 품종간(品種間) 저수온에 대한 반응은 뚜렷한 차이(差異)를 보여 농백(農白)은 $17^{\circ}C$에서 수량을 기대(期待)할 수 없었고 $17{\sim}20^{\circ}C$사이에서는 생식생장(生殖生長)이 가능(可能)하여 수량을 낼 수 있었으며 $21^{\circ}C$에서는 정상적(正常的)인 생육(生育)과 수량성을 보였다. 그러나 밀양(密陽)23호(號)는 $19^{\circ}C$에서도 정상적(正常的)인 생식생장(生殖生長)이 이루어지지 못하여 수량을 기대(期待) 할 수 없었다.

• Structural Engineering and Mechanics
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• 제14권3호
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• pp.331-343
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• 2002

Because of the increasing span of arch bridges, ultimate capacity analysis recently becomes more focused both on design and construction. This paper investigates the static and ultimate behavior of a long-span steel arch bridge up to failure and evaluates the overall safety of the bridge. The example bridge is a long-span steel arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any arch bridge in the world. Ultimate behavior of the example bridge is investigated using three methods. Comparisons of the accuracy and reliability of the three methods are given. The effects of material nonlinearity of individual bridge element and distribution pattern of live load and initial lateral deflection of main arch ribs as well as yield stresses of material and changes of temperature on the ultimate load-carrying capacity of the bridge have been studied. The results show that the distribution pattern of live load and yield stresses of material have important effects on bridge behavior. The critical load analyses based on the linear buckling method and geometrically nonlinear buckling method considerably overestimate the load-carrying capacity of the bridge. The ultimate load-carrying capacity analysis and overall safety evaluation of a long-span steel arch bridge should be based on the geometrically and materially nonlinear buckling method. Finally, the in-plane failure mechanism of long-span steel arch bridges is explained by tracing the spread of plastic zones.

• 국제강구조저널
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• 제18권5호
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• pp.1617-1630
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• 2018

The crucial differences between conventional rail with split-type connectors and continuous welded rails are axial stress in the longitudinal direction and stability, as well as other issues generated under the influence of loading effects. Longitudinal stresses generated in continuously welded rails on railway bridges are strongly influenced by the nonlinear behavior of the supporting system comprising sleepers and ballasts. Thus, the track structure interaction cannot be neglected. The rail-support system mentioned above has properties of non-uniform material distribution and uncertainty of construction quality. The linear elastic hypothesis therefore cannot correctly evaluate the stress distribution within the rails. The aim of this study is to apply the nonlinear finite element method using the nonlinear coupling interface between the track and structural model and to illustrate the welded rail behavior under the loading effect and uncertain factors of the ballast. Numerical results of nonlinear finite analysis with a three-dimensional solid and frame element model are presented for a typical track-bridge system. A composite plate girder, modeled by solid and shell elements, is also analyzed to consider the behavior of the welded rail. The analysis result showed buckling under the independent calculations of load cases, including 'temperature change', 'bending of the supporting structure', and 'braking' of the railway vehicle. A parametric study of the load combination method and the loading sequence is also included in this analysis.

• 한국항공우주학회지
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• 제30권5호
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• pp.9-14
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• 2002

열-기계-전기 하중이 완전 연계된 스마트 구조물의 응력과 변형을 정확히 예측할 수 있는 판 이론을 개발하였다. 두께 방향으로 변위와 온도장은 3차 곡선에 선형 지그재그 장을 중첩하여 구하였다. 횡 수직방향 변형을 고러하기 위해 횡 수직 변위를 두께방향으로, 포물선으로 가정하였다. 전기장은 선형지그재그 형태로 가정하였다. 스마트 구조물의 층에 의존하는 변위장과 온도장의 자유도를 층 사이의 연속조건과, 평판의 위 아래 횡 방향 전단응력이 존재하지 않는다는 조건으로부터, 기준면에 의한 자유도로 나타내었다. 수치 예를 통해 제안된 이론의 정확도와 효율성을 평가하였다. 본 연구에서 제시한 고차 지그재그 이론은 열 환경 하에서 두꺼운 지능 복합재료 평판의 정적, 동적 거동 해석에 사용될 수 있다.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.157-172
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• 2013

This paper presented an investigation of macromolecular suspension in a grooved channel by using the dissipative particle dynamics (DPD) with finitely extensible non-linear elastic (FENE) bead spring chains model. Before studying the movement and evolution of macromolecules, the DPD method was first validated by modeling the simple fluid flow in the grooved channel. For both simple fluid flow and macromolecular suspension, the flow fields were analyzed in detail. It is found that the structure of the grooved channel with sudden contraction and expansion strongly affects the velocity distribution. As the width of the channel reduces, the horizontal velocity increases simultaneously. Vortices can also be found at the top and bottom corners behind the contraction section. For macromolecular suspension, the macromolecular chains influence velocity and density distribution rather than the temperature and pressure. Macromolecules tend to drag simple fluid particles, reducing the velocity with density and velocity fluctuations. Particle trajectories and evolution of macromolecular conformation were investigated. The structure of the grooved channel with sudden contraction and expansion significantly influence the evolution of macromolecular conformation, while macromolecules display adaptivity to adjust their own conformation and angle to suit the structure so as to pass the channel smoothly.

• 암석학회지
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• 제5권2호
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• pp.161-167
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• 1996

The CSD (crystal size distribution) of diopside crystals in the calc-silicate hornfels of the Hwanggangni Formation intruded by the Cretaceous Daeyasan granite shows the patterns of continuous nucleation and growth. There is correlation between the distance from the intrusion contact and the slopes from the linear part of log(population density) vs. size diagrams. In the log(population density) vs. size diagrams of the samples systematically collected from the intrusion contact, two different groups are recognized; the slopes for the samples near the intrusion contact (horizontal distance from the contact less than 50m) are gentler (1500$cm^{-1}$) than those for the samples away from the intrusion contact (2500$cm^{-1}$, distance from the contact greater than 100 m). These differences may reflect the differences in growth rates and crystallization time, or the differences in diopside-forming reactions. All of the log(population density) vs. size diagrams show depletion of smaller crystals. The observed depletion may be due to Ostwald ripening or the changes in nucleation rates as the reactant phases diminishes. Similar grouping is also possible for the observed degree of depletion of smaller crystals; the depletion decreases with increasing distance from the intrusion contact, suggesting temperature-dependent rates of Ostwald ripening.