• Title/Summary/Keyword: 배향함수

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Reliability Analysis of GFRP Laminated Composite Cylindrical Shells (GFRP적층복합재료관의 신뢰성 해석)

  • 조효남;이승재
    • Computational Structural Engineering
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    • v.6 no.1
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    • pp.117-125
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    • 1993
  • In general, the strength and stiffness of laminated composite cylindrical shells are very sensitive to the variation of slenderness parameters, some coupling-stiffness parameters, lamination angles, stacking sequence and number of layers. In this paper, the effects of these factors on the strength and buckling reliabilities of GFRP laminated cylindrical shells are investigated based on the proposed strength and buckling limit state models. As these factors have various and complicated effects on the strength and buckling reliabilities of GFRP laminated cylindrical shells, the results should be incorporated into the design formula such that optimum design technique and design code which provide uniform consistent reliability for balanced design in practice

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Three-Dimensional Vibration Analysis of Cantilevered Laminated Composite Plates (캔틸레버 복합 적층판의 3차원 진동해석)

  • 김주우;정희영
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.14 no.3
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    • pp.299-308
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    • 2001
  • This paper presents the three-dimensional (3-D) study of the natural vibration of cantilevered laminated composite plates. The Ritz method is used to obtain stationary values of the associated Lagrangian functional with displacements approximated by mathematically complete polynomials satisfying the boundary conditions at the clamped edge exactly. The accuracy of the 3-D model is established through a convergence study of non-dimensional frequencies followed by a comparison of the converged 3-D solutions with analytical and experimental findings in the existing literature. A wide scope of 3-D frequency results explain the influence of a number of geometrical and material parameters for cantilevered laminated plates, namely aspect ratio (a/b), width-to-thickness ratio (a/h), orthotropy of material, number of plies (NP), fiber orientation angle(θ), and stacking sequence.

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The alignment of Sr-ferrite magnetic powder in anisotropic Sr-ferrite/resin-bonded magnets (이방성 Sr-페라이트/ 레진본드 영구자석에서 Sr-페라이트 자성분말의 방향성)

  • 정원용;조태식;문탁진
    • Journal of the Korean Magnetics Society
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    • v.4 no.3
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    • pp.219-225
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    • 1994
  • The alignment of Sr-ferrite magnetic powders, which is usually related to the fluidity and the applied magnetic field, is investicated in the anisotropic Sr-ferrite / resin-bonded permanent magnets. The magnetic powder alignment is observed to increase with the applied magnetic field and the fluidity which is a function of molding temperature and powder packing ratio. The best magnetic powder alignment is achieved at the following conditions; Sr-ferrite packing ratio of 56vol%, apparent viscosity of about 3000 poise in $1000sec^{-1}$ shear rate, and applied magnetic field of about 5kOe. The degree of preferred orientation of the magnetic powders in the field direction, as determined by the dc hysterisis graphs, is 84~85% (0.84~0.85). This result is in agreement with the value of 0.85 obtained by the X-ray experiments in the $2{\theta}$ range of ${23~40}^0$. The best magnetic properties obtained are:2.2kG of remanent flux density, 2.2MGOe of maximum energy product.

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Effects of Strain-Induced Crystallization on Mechanical Properties of Elastomeric Composites Containing Carbon Nanotubes and Carbon Black (탄소나노튜브 및 카본블랙 강화 고무복합재료의 변형에 의한 결정화가 기계적 특성에 미치는 영향)

  • Sung, Jong-Hwan;Ryu, Sang-Ryeoul;Lee, Dong-Joo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.9
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    • pp.999-1005
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    • 2011
  • The effects of strain-induced crystallization (SIC) on the mechanical properties of elastomeric composites as functions of extension ratio (${\lambda}$), multiwalled carbon nanotube (CNT) content, and carbon black (CB) content are investigated. The differential scanning calorimetry (DSC) analysis shows that the degree of crystallinity increases with the increase in the CB and CNT content. As ${\lambda}$ increases, the glass transition temperature (Tg) of the composites increases, and the latent heat of crystallization (LHc) of the composites is maximum at ${\lambda}$=1.5. It is found that the mechanical properties have a linear relation with LHc, depending on the CNT content. According to the TGA (thermogravimetric analysis), the weight loss of the composite matrix is 94.3% and the weight of the composites decreases with the filler content. The ratio of tensile modulus ($E_{comp}/E_{matrix}$) is higher than that of tensile strength (${\sigma}_{comp}/{\sigma}_{matrix}$) because of the CNT orientation inside the elastomeric composites.

Study on the Physical and Mechanical Properties of Particleboard and Oriented Strandboard Manufactured by Tulliptree (Liriodendron tulipifera L.) (백합나무를 이용하여 제조한 3층 파티클보드와 배향성 스트랜드보드(OSB)의 물성에 관한 연구)

  • Seo, Jun won;Gang, Gil woo;Jo, Gun hee;Park, Heon
    • Journal of the Korean Wood Science and Technology
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    • v.46 no.1
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    • pp.67-72
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    • 2018
  • This study was conducted to investigate a potential of Yellow poplar (Liriodendron tulipifera L.) as a raw material for the manufacturing of particleboard (PB) and oriented strandboard (OSB). PB panels were prepared at the parameters of $0.7g/cm^3$ density, 15 mm thickness, three-layer, $E_1$ grade urea-formaldehyde (UF) resin, emulsion wax, and hardener. OSB panels were manufactured with a density of $0.65g/cm^3$, thickness of 10 mm, and $E_1$ grade of UF resin. Particle size of the face layer of PB was 20~80 mesh with 7~9% moisture content (MC), while that of core-layer was 3~20 mesh with 3~5% MC, which was similar to the production condition of commercial PB. As a result, the manufactured PB panels with 15.8 mm thickness, $0.7g/cm^3$ density, and 5.8% MC satisfied the requirement of bending strength of 15 type PB of Korean Industrial Standard (KS F 3104). Both internal bonding (IB) strength and surface screw withdrawal resistance also satisfied the requirement of 18 type PB of the standard. But, the edge screw withdrawal resistance satisfied the requirement of 15 type PB of the standard. These differences in properties could be due to the slenderness ratio of raw particles. In case of OSB panels with 10.7 mm thickness, $0.68g/cm^3$ density, and 5.8% MC satisfied all the requirements of bending strength, screw withdrawal resistance, and IB strength of 18 type PB of the standard. These results suggest that Yellow poplar wood has a good potential as a raw material for the production of PB and OSB.

Hydrogen Bond Effect on Chain Behavior at the Semidilute Regime of Poly(vinyl alcohol) Aqueous Solution (폴리(비닐 알코올) 수용액의 준희박농도 영역에서 사슬 거동에 대한 수소결합의 효과)

  • Park Il-Hyun;Yu Young-Chol;Park Ki-Sang;Lee Dong-Il;Lyoo Won-Seok
    • Polymer(Korea)
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    • v.30 no.3
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    • pp.271-278
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    • 2006
  • In order to investigate the structure and dynamics of atatic poly (vinyl alcohol) (PVA)/water system, laser light scattering experiment has been done in the semi-dilute concentration regime at $25^{\circ}C$. The scattering intensity I(q) can be analyzed with the fractal equation of $I(q){\sim}q^{-m}$ instead of Onstein-Zernike type equation. The fractal dimensionality m was found to be constant after reaching the plateau value of $m=2.6{\pm}0.3$ above C=3wt%. The time correlation function of dynamic light scattering has always two different modes such as fast mode and slow one. The cooperative diffusion of fast mode showed concentration independence contrary 4o the reptation theory's concentration dependent exponent of 3/4. The slow mode can be interpreted as the motion of large scale heterogeneities and its strong concentration dependence is apparent with a large negative exponent of -3.0. It is considered that the stereo-regular arrangement with four successive meso units of -OH plays as a key role in forming such heterogeneity.

Theoretical Studies on Orbital Interactions and Conformation of ${\alpha}$-Substituted Acetones (${\alpha}$-치환 아세톤의 궤도간 상호작용과 형태에 관한 이론적 연구)

  • Ikchoon Lee;Kiyull Yang;Wang Ki Kim;Byung Hoo Kong;Byung Choon Lee
    • Journal of the Korean Chemical Society
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    • v.30 no.1
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    • pp.9-18
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    • 1986
  • MNDO and STO-3G calculations were performed to determine relative stabilities of rotamers for ${\alpha}$-substituted acetones, $CH_2XCOCH_3$, X = F, Cl, OH, SH, and $NH_2$. It was found that rotamers corresponding to gauche forms are preferred for all the ${\alpha}$-substituents except for X = F and NH$_2$, for which the cis forms were the preferred ones. The stability of gauche form was dictated by the stabilizing two-orbital-two-electron interaction ${\sigma}_{cx}$-${\pi}_{co}^*$, operating uniquely in the gauche form due to the substantial vicinal overlap and energy gap narrowing between ${\sigma}_{cx}$ and ${\pi}_{co}^*$ orbitals. The energy gap narrowing was caused by the lowering of ${\pi}_{co}^*$ level due to the hyperconjugative ${\sigma}_{cx}^*$-${\pi}_{co}^*$ interactions; the red shift in the n-${\pi}^*$ transition was another effect of the relatively large ${\sigma}_{cx}^*$-${\pi}_{co}^*$ splitting. Various ${\sigma}-{\pi}$ interactions in the gauche form were found to be stronger in the third-row hetero atom system, X = Cl and SH. Interactions between nonbonding orbital on N, $n_N$ and vicinal C-C ${\sigma}$ bond were shown to be stronger in the trans than in the cis orientation.

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Classification of Ground Subsidence Factors for Prediction of Ground Subsidence Risk (GSR) (굴착공사 중 지반함몰 위험예측을 위한 지반함몰인자 분류)

  • Park, Jin Young;Jang, Eugene;Kim, Hak Joon;Ihm, Myeong Hyeok
    • The Journal of Engineering Geology
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    • v.27 no.2
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    • pp.153-164
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    • 2017
  • The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.