• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.97-107
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• 2003

To obtain a more accurate response from larninated composite structures, the effect of transverse shear deformation, transverse normal strain/stress, and nonlinear variation of in-plane displacements vis-$\\grave{a}$-vis the thickness coordinate should be considered in the analysis. The improved higher-order theory was used to determine the critical buckling load and natural frequencies of laminated composite structures. Solutions of simply supported laminated composite plates and sandwiches were obtained in closed form using Navier's technique, with the results compared with calculated results using the first order and other higher-order theories. Numerical results were presented for fiber-reinforced laminates, which show the effects of ply orientation, number of layers, side-toithickness ratio, and aspects ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.12
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• pp.1229-1235
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• 2015

Scaffold fabrication technology using a 3D printer was developed for damaged bone tissue regeneration. A scaffold for bone tissue regeneration application should be biocompatible, biodegradable, and have an adequate mechanical strength. Moreover, the scaffold should have pores of satisfactory quantity and interconnection. In this study, we used the polymer deposition system (PDS) based on fused deposition modeling (FDM) to fabricate a 3D scaffold. The materials used were polycaprolactone (PCL) and alginic acid sodium salt (sodium alginate, SA). The salt-leaching method was used to fabricate dual pores on the 3D scaffold. The 3D scaffold with dual pores was observed using SEM-EDS (scanning electron microscope-energy dispersive spectroscopy) and evaluated through in-vitro tests using MG63 cells.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.630-648
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• 1992

The minimum weight design for simply-supported isotropic or symmetrically laminated stiffened cylindrical shells subjected to various loads (axial compression or combined loads) is studied by a nonlinear mathematical search algorithm. The minimum weight design in accomplished with the CONMIN optimizer by Vanderplaats. Several types of buckling modes with maximum allowable stresses and strains are included as constraints in the minimum weight design process, such as general buckling, panel buckling with either stingers or rings smeared out, local skin buckling, local crippling of stiffener segments, and general, panel and local skin buckling including stiffener rolling. The approach allows the consideration of various shapes of stiffening members. Rectangular, I, or T type stringers and rectangular rings are used for stiffened cylindrical shells. Several design examples are analyzed and compared with those in the previous literatures. The unstiffened glass/epoxy, graphite/epoxy(T300/5208), and graphite/epoxy aluminum honeycomb cylindrical shells and stiffened graphite/epoxy cyindrical shells under axial compression are analyzed through the present approach.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.1
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• pp.25-28
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• 2000

The InAs self-assembled quantun dots (SAQDS) were grown on a GaAs(100) substrate using a molecular beam epitaxy (MBE) technique. The InAs QDs were multi-stacked to have various layer structures of 1, 3, 6, 10, 15 and 20 layers, where the thickness of the GaAs spacer and InAs QD layer were 20 monolayers (MLs) and 2 MLs, respectively. The nanostructured feature was characterized by photoluminescence (PL) and scanning transmission electron microscopy (STEM). It was found that the highest PL intensity was obtained from the specimen with 6 stacking layers and the energy of the PL peak was split with increasing the number of stacking layers. The STEM investigation exhibited that the quantum dots in the 6 stacking layer structure were well aligned in vertical columns without any deflect generation, whereas the volcano-like deflects were formed vertically along the growth direction over 10 periods of InAs stacking layers.

• Composites Research
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• v.12 no.1
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• pp.1-10
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• 1999

In order to predict the dynamic behavior of composite laminated plate accurately, the parametric identification is performed using its mechanical properties- $E_1,\;E_2,\;V_{12},\;G_{12}$ as design parameters. After natural frequencies are measured through simple vibration test, the objective function consists of the sum of errors between experimental and numerical frequencies of a structure. As optimization algorithm, conjugate gradient method is used to minimize the objective function. Sensitivity Analysis is performed to update design parameters during this process and can explain the result of parametric identification. In order to check the propriety of result, mode shapes are compared before and after identification. The improved prediction of natural frequencies of composite laminated plate is obtained with updated properties. For the application of result, updated properties is applied to the composite laminated plate that has different stacking sequence.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.219-224
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• 2017

This paper investigates equivalent stress and deformation happening at inner fiber structure when the tensile force acts on the specimen with arch type composed of carbon fiber. The countless many each fiber is applied on the unidirectional axis at CFRP and has the high specific strength and stiffness by comparing with iron. In this study, the distribution of stress due to radius is investigated at the structure of arch type composed with the optimum stacking angle of $60^{\circ}$. And the durability is seen to be lower as the radius increases at the same stacking angle. By applying the result of this study to the design of structure with arch type, it can be devoted to the safe design for the prevention of damage and the durabilty improvement. And it is possible to be grafted onto the convergence technique at the designed factor and show the esthetic sense.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.161-171
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• 2006

paper presents the results of a three-dimensional study of the natural vibration of laminated composite rectangular plates with various combinations of clamped and free boundaries. The Ritz method was used to obtain the stationary values of the associated Lagrangian, with displacements approximated using mathematicaly complete, characteristic orthogonal polynomials. The correctness of the three-dimensional model was established through a convergence study of the non-dimensional frequencies, followed by a comparison of the analytical findings in the existing literature. The wide scope of additional three-dimensional frequency results explains the influence of a number of geometrical and material parameters for angle-ply and cross-ply laminated plates, namely aspect ratio (${\mathcal{a/b}}$), thickness ratio (${\mathcal{a/h}}$), orthotropy of material, number of plies (${\mathcal{N}}$), fiber orientation angle (${\theta}$), and stacking sequence.

• Composites Research
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• v.19 no.2
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• pp.20-27
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• 2006

The hybrid composite materials with non-woven tissue (NWT) was developed to improve the mechanical properties of conventional FRP composite materials. The hybrid prepreg with NWT consists of FRP prepreg and NWT prepreg. The NWT prepreg consists of NWT and polymer resin. The NWT has short fibers, discretely distributed with in-plane random orientation fibers. The purposes of this study of hybrid prepreg with NWT are (i) to increase the interlaminar properties(the fracture toughness and strength), (ii) to improve the mechanical properties and reliability, while maintaining a low cost, (iii) to introduce a tough and strong interlayer at critical positions to be required of strength in the laminate. To accomplish the above purposes, a production technique to decrease voids in NWT layers was proposed in this paper. The interlaminar failure characteristics of laminated composite materials was tremendously improved by hybrid concept with NWT.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.81-85
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• 2017

Fiber-reinforced polymer composites, which are made by combining a continuous fiber that acts as reinforcement and a homogeneous polymeric material that acts as a host, are engineering materials with high strength and stiffness and a lightweight structure. In this study, a shape memory alloy(SMA) reinforced composite actuator is presented. This actuator is used to generate large deformations in single lightweight structures and can be used in applications requiring a high degree of adaptability to various external conditions. The proposed actuator consists of numerous individual laminas of the glass-fiber fabric that are embedded in a polymeric matrix. To characterize its deformation behavior, the composition of the actuator was changed by changing the matrix material and the number of the glass-fiber fabric layers. In addition, current of various magnitudes were applied to each actuator to study the effect of the heating of SMA wires on applying current.

• Journal of Korean Society of Steel Construction
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• v.13 no.1
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• pp.53-60
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• 2001

Theories for advanced composite structures are too difficult for such design engineers for construction and some simple but accurate enough methods are necessary. The senior author has reported that some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. For such plates the fiber orientations given above behave as specially orthotropic plates and simple formulas developed by the senior author. Most of the bidge and building slabs on girders have large aspect ratios For such cases frurther simplification is possible by neglecting the effect of the longitudinal moment terms(Mx) on the relevant partial differential equationsof equilibrium In this paper, the result of the study on the subject problem is presented.