• Steel and Composite Structures
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• v.28 no.5
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• pp.589-606
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• 2018

The previous studies reflected the significant effect of neutral-axis position and coupling of in-plane and out-of-plane displacements on behavior of functionally graded (FG) nanobeams. In thin FG beam, this coupling can be eliminated by a proper choice of the reference axis. In shear deformable FG nanobeam, not only this coupling can't be eliminated but also the position of neutral-axis is dependent on through-thickness distribution of shear strain. For the first time, in this paper it is avoided to guess a shear strain shape function and the exact shape function and consequently the exact position of neutral axis for arbitrary gradation of higher order nanobeam are obtained. This paper presents new methodology based on differential transform and collocation methods to solve coupled partial differential equations of motion without any simplifications. Using exact position of neutral axis and higher order beam kinematics as well as satisfying equilibrium equations and traction-free conditions without shear correction factor requirement yields to better results in comparison to the previously published results in literature. The classical rule of mixture and Mori-Tanaka homogenization scheme are considered. The Eringen's nonlocal continuum theory is applied to capture the small scale effects. For the first time, the dependency of exact position of neutral axis on length to thickness ratio is investigated. The effects of small scale, length to thickness ratio, Poisson's ratio, inhomogeneity of materials and various end conditions on vibration and buckling of local and nonlocal FG beams are investigated. Moreover, the effect of axial load on natural frequencies of the first modes is examined. After degeneration of the governing equations, the exact new formulas for homogeneous nanobeams are computed.

• Steel and Composite Structures
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• v.18 no.6
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• pp.1493-1515
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• 2015

A new refined hyperbolic shear deformation theory (RHSDT), which involves only four unknown functions as against five in case of other shear deformation theories, is presented for the thermoelastic bending analysis of functionally graded sandwich plates. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich plate faces are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson's ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Several kinds of sandwich plates are used taking into account the symmetry of the plate and the thickness of each layer. The influences played by the transverse shear deformation, thermal load, plate aspect ratio and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal-ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.198-198
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• 2006

Tin doped $In_2O_3$ sputtering target is widely used to produce a various kinds of flat panel display because of high transmittance in visible region and high electrical conductivity. In2O3 and SnO2 powders were prepared by a homogeneous precipitation method using metal source, respectively, the calcining and sintering behavior of the indium-tin oxide(In2O3-SnO2) composite powders were studied. The tin oxide(SnO2) dispersion condition in ITO sputtering target was improved by increasing calcining temperature. And the tin oxide dispersion was also improved by reducing the tin oxide contents in the ITO target from 30 to 5wt%. SnO2 dispersion and densification of ITO target is very difficult to control due to sublimation of SnO2 at over 1150C.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.309-314
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• 2003

A spark plasma sintering technique has been used for the fabrication of $Al_2O_3$-SiC nanocomposites at the low temperature of $1100^{\circ}C$∼$1500^{\circ}C$. The sintered $Al_2O_3$-SiC composites shows very homogeneous microstructure without any particular abnormal grain growth, indicating that the addition of nano-sized SiC particles is very effective to control grain growth and to induce the residual stress in the $Al_2O_3$ matrix, resulting in the intragranular fracture. These SiC particles are present in the grain boundaries and also intragrain, depending on the sintering condition, and improve remarkably the mechanical properties of $Al_2O_3$-SiC composite through the mechanisms of strengthening and toughening induced by crack diffraction and crack bridging.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3474-3490
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• 1996

A metal matrix composites(MMCs) for A16061 reinforced with silicon carbide particles is fabricated by melt-stirring method. The primary products of MMCs billets are prepared by volume fractions 5 vol% to 20 vol% and particle size $13\mu m$ to $22\mu m$.This paper will be made to examine the microstructure and mechanical properties of fabricated $SiC_p$/Al 6061 composite by melt-stirring and squeeze casting method. The MMC billets is extruded at $500^{\circ}C$ under the constant extrusion velocity $V_e$=2mm/min using curved shape die. Extrusion force, particle rearrangement, micro structure and mechanical properties of extruded composites will be investigated. The mechanical properties of primary billets manufactured by melt-stirring and squeeze casting method will be compared with extrusion specimen. The effect of volume fraction and size of the reinforcements will be studied. The increase in uniformity of particle dispersion is the major reason for an improvement in reliability due to hot extrusion with optimal shape die. Experimental Young's modulus and 0.2% offset yield strength for the extruded MMCs will be compared with theretical values calculated by the Eshelby method. A method will be proposed for the prediction of Young's modulus and yield strength in $SiC_p$ reinforced MMCs.

• Steel and Composite Structures
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• v.35 no.1
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• pp.61-76
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• 2020

In this paper, the dynamic behaviour of an inclined functionally graded material (FGM) beam with different boundary conditions under a moving mass is investigated based on the first-order shear deformation theory (FSDT). The material properties vary continuously along the beam thickness based on the power-law distribution. The system of motion equations is derived by using Hamilton's principle. The finite element method (FEM) is adopted to develop a general solution procedure. The moving mass is considered on the top surface of the beam instead of supposing it on the mid-plane. In order to consider the Coriolis, centrifugal accelerations and the friction force, the contact force method is used. Moreover, the effects of boundary conditions, the moving mass velocity and various material distributions are studied. For verification of the present results, a comparative fundamental frequency analysis of an FGM beam is conducted and the dynamic transverse displacements of the homogeneous and FGM beams traversed by a moving mass are compared with those in the existing literature. There is a good accord in all compared cases. In this study for the first time in dynamic analysis of the inclined FGM beams, the Coriolis and centrifugal accelerations of the moving mass are taken into account, and it is observed that these accelerations can be ignored for the low-speeds of the moving mass. The new provided results for dynamics of the inclined FGM beams traversed by a moving mass can be significant for the scientific and engineering community in the area of FGM structures.

• Steel and Composite Structures
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• v.16 no.6
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• pp.559-576
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• 2014

A new mathematical model and its finite element formulation for the non-linear stress-strain analysis of a planar beam strengthened with plates bolted or adhesively bonded to its lateral sides is presented. The connection between the layers is considered to be flexible in both the longitudinal and the transversal direction. The following assumptions are also adopted in the model: for each layer (i.e., the beam and the side plates) the geometrically linear and materially non-linear Bernoulli's beam theory is assumed, all of the layers are made of different homogeneous non-linear materials, the debonding of the beam from the side-plates due to, for example, a local buckling of the side plate, is prevented. The suitability of the theory is verified by the comparison of the present numerical results with experimental and numerical results from literature. The mechanical response arising from the theoretical model and its numerical formulation has been found realistic and the numerical model has been proven to be reliable and computationally effective. Finally, the present formulation is employed in the analysis of the effects of two different realizations of strengthening of a characteristic simply supported flexural beam (plates on the sides of the beam versus the tension-face plates). The analysis reveals that side plates efficiently enhance the bearing capacity of the flexural beam and can, in some cases, outperform the tensile-face plates in a lower loss of ductility, especially, if the connection between the beam and the side plates is sufficiently stiff.

• Composites Research
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• v.23 no.5
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• pp.8-14
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• 2010

Three types of glass woven fabrics (plain, balanced twill, and unbalanced twill) having various sample sizes and aspect ratios were tested using the bias-extension tests. Real-time deformation images, force, and displacement data were collected. For the bias-extension test, the shear angle of the fabrics from the equation based on the crosshead displacement and fabric size was compared with direct manual measurements of the warp and weft angles as well as the optical measurement software. To determine the shear force, an analytical equation was introduced considering the kinematics of the bias-extension test. The obtained shear behaviors were further compared with the results by the trellis-frame test. The optical measurement methods showed that the mathematical method was reasonable before the shear angle of the fabrics reaches $30^{\circ}$ in the bias-extension tests. Also, the bias-extension test gave consistent behaviors with the trellis-frame test only for isotropic and homogeneous fabrics such as balanced plain and twill weaves.

• Journal of Broadcast Engineering
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• v.8 no.1
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• pp.91-100
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• 2003

In this paper, to improve the retrieval Performance, an efficient combination of the MPEG-7 visual descriptors, such as the edge histogram descriptor (EHD), the color layout descriptor (CLD), and the homogeneous texture descriptor (HTD), is proposed in the framework of the relevance feedback approach. The EHD represents spatial distribution of edges in local image regions and it is considered as an important feature to represent the content of the image. The CLD specifies spatial distribution of colors and is widely used in image retrieval due to its simplicity and fast operation speed. The HTD describes precise statistical distribution of the image texture. Both the feature vector for the query image and the weighting factors among the combined descriptors are adaptively determined during the relevance feedback. Experimental results show that the proposed method improves the retrieval performance significantly tot natural images.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.65-73
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• 2006

The high temperature occurs due to the combustion gas from engine in unmanned aerial vehicles (UAV). The high temperature may cause serious damages in UAV structure. The Functionally Graded Material (FGM) is chosen as a candidate material of the engine duct structure. A functionally graded material (FGM) is a two- component mixture composed by compositional gradient materials from one material to the other. In contrast, traditional composite materials are homogeneous mixtures, and involve compositions between the desirable properties of the component materials. Since significant proportions of an FGM contain the pure form of each material, the need for compromise is eliminated. The properties of both components can be fully utilized. Thermal stress analysis of FGM layers (20, 40, 60, 80 and 100) is performed in this paper. In addition, the creep behavior of FGM applied in duct structure of an engine is analyzed for better understanding of FGM characteristics.