• Structural Engineering and Mechanics
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• 제51권5호
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• pp.867-891
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• 2014

An equivalent single layer trigonometric shear deformation theory taking into account transverse shear deformation effect as well as transverse normal strain effect is presented for static flexure of cross-ply laminated composite and sandwich plates. The inplane displacement field uses sinusoidal function in terms of thickness coordinate to include the transverse shear deformation effect. The cosine function in thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. The kinematics of the present theory is much richer than those of the other higher order shear deformation theories, because if the trigonometric term (involving thickness coordinate z) is expanded in power series, the kinematics of higher order theories (which are usually obtained by power series in thickness coordinate z) are implicitly taken into account to good deal of extent. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The closed-form solutions of simply supported cross-ply laminated composite and sandwich plates have been obtained. The results of present theory are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.153-163
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• 2019

Longitudinal fracture behavior of non-linear elastic beam configurations is studied in terms of the strain energy release rate. It is assumed that the beams exhibit continuous material inhomogeneity along the width as well as along the height of the crosssection. The Ramberg-Osgood stress-strain relation is used for describing the non-linear mechanical behavior of the inhomogeneous material. A solution to strain energy release rate is derived that holds for inhomogeneous beams of arbitrary cross-section under combination of axial force and bending moments. Besides, the solution may be applied at any law of continuous distribution of the modulus of elasticity in the beam cross-section. The longitudinal crack may be located arbitrary along the beam height. The solution is used to investigate a longitudinal crack in a beam configuration of rectangular cross-section under four-point bending. The crack is located symmetrically with respect to the beam mid-span. It is assumed that the modulus of elasticity varies continuously according a cosine law in the beam cross-section. The longitudinal fracture behavior of the inhomogeneous beam is studied also by applying the J-integral approach for verification of the non-linear solution to the strain energy release rate derived in the present paper. Effects of material inhomogeneity, crack location along the beam height and non-linear mechanical behavior of the material on the longitudinal fracture behavior are evaluated. Thus, the solution derived in the present paper can be used in engineering design of inhomogeneous non-linear elastic structural members to assess the influence of various material and geometrical parameters on longitudinal fracture.

• 한국산학기술학회논문지
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• 제16권9호
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• pp.5843-5849
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• 2015

본 연구는 단감농가의 생산비절감방안 모색을 위해 생산요소 수요구조를 분석했다. 2001~2013년간 농산물소득조사 원자료를 이용해 초월대수 비용함수를 추정하고 노동, 자본, 중간투입재간 가격 및 대체탄력성을 계측했다. 분석결과 생산요소 모두 가격변화에 따른 수요변화가 크지 않고 특히 비용부담이 가장 큰 노동의 가격상승에 따른 타 생산요소의 대체성이 낮아 구조적으로 단기간에 노동 수요를 줄이기는 어려운 것으로 나타났다. 이는, 생산비절감을 위해서는 노동에 비해 수요가 탄력적인 중간투입재, 특히 탄력성이 큰 비료와 기타재료비를 중심으로 비용절감이 이뤄져야함을 시사한다.

• Advances in nano research
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• 제8권1호
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• pp.13-24
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• 2020

In this paper, for the first time based on the nonlocal strain gradient theory the effect of size dependency in torsional vibration of bi-direction functionally graded (FG) nonlinear nano-cone is study. The material properties were assumed to vary according to the arbitrary function in radial and axial directions. The Navier equation and boundary conditions of the size-dependent bidirectional FG nonlinear nano-cone were derived by Hamilton's principle. These equations were solved by employing the generalized differential quadrature method (GDQM). The presented model can turn into the classical model if the material length scale parameters are taken to be zero. The effects of some parameters, such as inhomogeneity constant, cross-sectional area parameter and small-scale parameters, were studied. As an essential result of this study can be stated that an FG nano-cone model based on the nonlocal elasticity theory behaves softer and based on the strain gradient theory behaves harder.

• 경영과정보연구
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• 제37권3호
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• pp.65-81
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• 2018

본 연구는 ARDL 모형을 이용하여 한국의 원유수요의 장기와 단기 자체가격, 교차가격 및 소득탄력성을 추정하였다. 첫째, ARDL-UECM의 한계검정결과에서 장기공적분관계가 종속변수인 원유수요와 독립변수인 자체가격과 교차가격 및 소득변수간에 존재하였다. 둘째, ARDL 모형(장기정태모형)을 통해 장기 모수들이 추정되었다. 셋째, 일부의 잔차의 자기상관이 존재하였으나, 반면에 설정오류가 발견되지 않았고 잔차항이 정규분포를 나타내었으며 이분산이 존재하지 않았고 CUSUM & CUSUMSQ 결과에서는 계수가 안정적이었다. 넷째, 추정된 원유수요에 대한 절대값으로 측정된 장기자체가격과 교차가격탄력성 및 소득탄력성은 모두 유의하며 1보다 크고 탄력적으로 민감하였으나, 반면에 단기자체가격과 교차가격탄력성 및 소득탄력성은 모두 유의하며 1보다 적고 비탄력적으로 민감하지 않았을지라도, 장기와 단기의 모든 탄력성들이 실제부호와 기대부호가 일치하였다. 다섯째, 국내의 일부 연구를 제외하고 대부분의 국외의 이전연구에서 단기자체가격과 교차가격 및 소득탄력성은 본 연구의 장기자체가격과 교차가격 및 소득탄력성보다 모두 더 낮다는 것을 확인하였다. 따라서 외국원유에 너무 의존하는 한국은 원유가격의 충격에 취약하게 되므로 유가 상승은 확실히 한국의 무역수지에 부정적인 영향을 미칠 수 있으므로 장기적 원유가격의 탄력성을 이용하여 한국의 원유수요를 효율적으로 통제하고 관리하는데 도움을 줄 수 있다고 사료된다. 시사점으로 원유와 관련한 국가별 정책변화 및 시장동향 모니터링의 강화, 국가별 정책 및 시장현황 맞춤형 진출전략의 수립, 신시장 개척 및 진출분야 다양화를 통한 적극적인 시장선점 노력의 강화 등이 필요하다.

• Food Science and Biotechnology
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• 제18권4호
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• pp.1027-1029
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• 2009

The aim of this research was to study the structural and rheological properties of gels formed by ferulated maize bran arabinoxylans (MBAX) at different concentrations. MBAX was cross-linked by a laccase leading to the formation of dimers and trimers of ferulic acid (di-FA, tri-FA) as covalent cross-link. An increase in MBAX gels elasticity (from 11 to 20 Pa) as well as lower mesh size (from 80 to 48 nm) were obtained by augmenting the MBAX concentration from 2.5 to 3.5%(w/v), respectively, but no increase in di-FA and tri-FA content was obtained (0.03 and 0.014 ${\mu}$g/mg MBAX, respectively).

• Structural Engineering and Mechanics
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• 제3권2호
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• pp.121-133
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• 1995

It is well known that two-dimensional simplified third-order theories satisfy the layer interface continuity of transverse shear strains, thus these theories violate the continuity of transverse shear stresses when two consecutive layers differ either in fibre orientation or material. The third-order theories considered herein involve four/or five dependent unknowns in the displacement field and satisfy the condition of vanishing of transverse shear stresses at the bounding planes of the plate. The objective of this investigation is to examine (i) the flexural response prediction accuracy of these third-order theories compared to exact elasticity solution (ii) the effect of layer interface continuity conditions on the flexural response. To investigate the effect of layer interface continuity conditions, three-dimensional elasticity solutions are developed by enforcing the continuity of different combinations of transverse stresses and/or strains at the layer interfaces. Three dimensional twenty node solid finite element (having three translational displacements as degrees of freedom) without the imposition of any of the conditions on the transverse stresses and strains is also employed for the flexural analysis of the laminated plates for the purposes of comparison with the above theories. These shear deformation theories and elasticity approaches in terms of accuracy, adequacy and applicability are examined through extensive numerical examples.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.737-746
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• 2020

This paper attempts to investigate the free vibration of functionally graded material beams with nonuniform width based on the nonlocal elasticity theory. The theoretical formulations are established following the Euler-Bernoulli beam theory, and the governing equations of motion of the system are derived from the minimum total potential energy principle using the nonlocal elasticity theory. In addition, the Differential Quadrature Method (DQM) is applied, along with the Chebyshev-Gauss-Lobatto polynomials, in order to determine the weighting coefficient matrices. Furthermore, the effects of the nonlocal parameter, cross-section area of the functionally graded material (FGM) beam and various boundary conditions on the natural frequencies are examined. It is observed that the nonlocal parameter and boundary conditions significantly influence the natural frequencies of the functionally graded material beam cross-section. The results obtained, using the Differential Quadrature Method (DQM) under various boundary conditions, are found in good agreement with analytical and numerical results available in the literature.

• Journal of the Korean Wood Science and Technology
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• 제49권5호
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• pp.504-513
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• 2021

In this study, cross-laminated wood panels were manufactured with four softwoods and three hardwoods with the goal of efficiently predicting the static strength performance using dynamic modulus of elasticity (MOE) and simultaneously revealing the dynamic performance of cross-laminated wood panels. The effect of the density of the species on the dynamic MOE of the laminated wood panels was investigated. Moreover, the static bending strength performance was predicted nondestructively through the correlation regression between the dynamic MOE and static bending strength performance. For the dynamic MOE, the parallel- and cross-laminated wood panels composed of oriental oak showed the highest value, whereas the laminated wood panels composed of Japanese cedar showed the lowest value. In all types of parallel- and cross-laminated wood panels, the density dependence was confirmed, and the extent of the density dependence was found to be greater in the P_⊥ and C_⊥ types with perpendicular-direction laminae in the faces than in the P_∥ and C_∥ types with longitudinal-direction laminae in the faces. Our findings confirmed that a high correlation exists at a significance level of 1% between the dynamic modulus and static bending modulus or bending strength in all types of laminated wood panels, and that the static bending strength performance can be predicted through the dynamic MOE.

• Structural Engineering and Mechanics
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• 제33권2호
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• pp.193-213
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• 2009

In this paper structural analysis of nonhomogeneous nanotubes has been carried out using nonlocal elasticity theory. Governing differential equations of nonhomogeneous nanotubes are derived. Nanotubes include both single wall nanotube (SWNT) and double wall nanotube (DWNT). Nonlocal theory of elasticity has been employed to include the scale effect of the nanotubes. Nonlocal parameter, elastic modulus, density and diameter of the cross section are assumed to be functions of spatial coordinates. General Differential Quadrature (GDQ) method has been employed to solve the governing differential equations of the nanotubes. Various boundary conditions have been applied to the nanotubes. Present results considering nonlocal theory are in good agreement with the results available in the literature. Effect of variation of various geometrical and material parameters on the structural response of the nonhomogeneous nanotubes has been investigated. Present results of the nonhomogeneous nanotubes are useful in the design of the nanotubes.