• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.90-100
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• 1993

A finite element formulation of vibration control of a laminated plate with piezoelectric sensor/ actuators is presented. Classical lamination theory with the induced strain actuation and Hamilton's principle are used to formulate the equations of motion of the system. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equations of motion and the total charge are discretized with 4 node, 12 degrees of freedom quadrilateral plate bending elements with one electrical degree of freedom. The mass and stiffness of the piezoelectric layer are introduced by treating them as another layer in laminated plate. Piezoelectric sensor/actuators are distributed, but discrete due to the geometry of electrodes. By defining an i.d. number of electrode for each element, modelling of electrodes with variable geometry can be achieved. The static response of a piezoelectric bimorph beam to electrical loading and sensor voltage to given displacement are calculated. For a laminated plate under the negative velocity feedback control, the direct time response by the Newmark-.betha. method and damped frequencies and modal damping ratios by modal state space analysis are derived.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.564-569
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• 2010

Highly anti-reflective optical property has been focussed in the field of thin film and display because of increasing demands to the high transparency and clearness of optical component. In this study, to obtain anti-reflective property, the formation of aluminium oxide with nanoscaled flowerlike frame structure was introduced as oxide material monolayer on the substrate by hydrothermal synthesis through sol-gel method. The properties of coating layer were measured by the means of UV-Vis spectroscopy, FT-IR spectroscopy, XRD, and FE-SEM. The morphology of coating layer in alumina-sol coated samples was controlled by hydrothermal temperature and time with aid of ultrasound. It was found that high transparency and anti-reflective optical properties were obtained the formation of flowerlike nanoframe structure.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.299-307
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• 2011

The offshore plants such as FPSO are subjected to combination loading of environmental conditions (swell, wave, wind and current). Therefore the fatigue damage is occurred in the operation time because the units encounter the environmental phenomena and the structural configurations are complicated. This paper is a research for frequency domain fatigue analysis of wide-band random loading focused on accuracy of fatigue damage estimation regarding the proposed methods. We selected ideal bi-modal spectrum. And comparison between time-domain fatigue analysis and frequency-domain fatigue analyses are conducted through the fatigue damage ratio. Fatigue damage ratios according to Vanmarcke's bandwidth parameter are founded for wide-band. Considering safety, we recommend that Jiao-Moan and Tovo-Benasciutti methods are optimal way at the fatigue design for wide-band response. But, it is important that these methods based on frequency-domain unstably change the accuracy according to the material parameter of S-N curve. This study will be background and guidance for the new frequency-domain fatigue analysis development in the future.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.555-564
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• 2004

Steel materials, which are normally used in bridge structures, are prone to corrosion and have thin plate structures. Steel bridges that have been damaged through increased vehicle load and corrosion are frequently expected to be strengthened. Repair or strengthening methods generally include cutting, bolting, and welding. The basic characteristics of stress and deformation behavior generated by cutting and welding in the course of the repair work, however, are not yet understood. It is difficult to say whether the safety of the structure after welding conforms with existing safety evaluation methods.Therefore, to gain confidence in the material and to guarantee the safety of the structure after welding, the stress generated by heat, through welding and cutting, was generalized. The effect of additional loads with respect to stress generated by heat was also investigated.

• Journal of the Korean Wood Science and Technology
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• v.37 no.1
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• pp.29-36
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• 2009

Recycling of wood wastes or residues is a good solution for a shortage of wood resources and a rise in the price. Shipbuilding wood wastes were almost used to produce the boards by milling. However, considering the economic value and insufficient resource, recycling with milling is dissatisfied method. This study has been carried out to investigate the recycling possibility of shipbuilding wood waste. There are two kinds of shipbuilding wastes: plywood waste and solid waste. From the results of this study, the following conclusions have been made: 1. Bending properties of plywood and laminated plywood lumber were tested by Korean Standard. 2. The main fracture mode of plywood waste and laminated plywood lumber is that of simple tension. 3. The recommended application for the recycling of shipbuilding wood waste are outdoor wood furnishings, indoor wood furnishings and some wooden building construction materials: interior raw material, wooden pallet, siding, paneling, flooring. picnic table, deck components, porch swing, landscaping timbers, residential fencing, patios, and boardwalks etc.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1181-1187
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• 2012

For the fatigue design of aircraft landing gear, the safe-life approach is applied. Structural defects such as cracks or detrimental deformations should not occur under the fatigue load spectrum depicting the entire lifetime usage of the aircraft. In the design phase, the fatigue life of the landing gear is estimated analytically by adopting the stress-based approach because the fatigue of aircraft landing gear is generally high-cycle fatigue. This utilizes S-N curves that are factored to produce design curves that account for the scatter and surface finish of the material. In the test and evaluation phases, a fatigue test should be conducted for full-scale landing gear to substantiate the fatigue design requirement in the end. In this study, the procedure for the fatigue test and evaluation of aircraft landing gear is presented with real application cases.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.411-419
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• 1999

It has been well recognized that a long term service at elevated temperature of $350^{\circ}C{\sim}550^{\circ}C$ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method (ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.490-490
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• 2011

Graphene, hexagonal network of carbon atoms forming a one-atom thick planar sheet, has been emerged as a fascinating material for future nanoelectronics. Huge attention has been captured by its extraordinary electronic properties, such as bipolar conductance, half integer quantum Hall effect at room temperature, ballistic transport over ${\sim}0.4{\mu}m$ length and extremely high carrier mobility at room temperature. Several approaches have been developed to produce graphene, such as micromechanical cleavage of highly ordered pyrolytic graphite using adhesive tape, chemical reduction of exfoliated graphite oxide, epitaxial growth of graphene on SiC and single crystalline metal substrate, and chemical vapor deposition (CVD) synthesis. In particular, direct synthesis of graphene using metal catalytic substrate in CVD process provides a new way to large-scale production of graphene film for realization of graphene-based electronics. In this method, metal catalytic substrates including Ni and Cu have been used for CVD synthesis of graphene. There are two proposed mechanism of graphene synthesis: carbon diffusion and precipitation for graphene synthesized on Ni, and surface adsorption for graphene synthesized on Cu, namely, self-limiting growth mechanism, which can be divided by difference of carbon solubility of the metals. Here we present that large area, uniform, and layer controllable graphene synthesized on Cu catalytic substrate is achieved by acetylene-assisted CVD. The number of graphene layer can be simply controlled by adjusting acetylene injection time, verified by Raman spectroscopy. Structural features and full details of mechanism for the growth of layer controllable graphene on Cu were systematically explored by transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy.

• Fire Science and Engineering
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• v.30 no.1
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• pp.17-23
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• 2016

Membrane structures can be used to create diverse lightweight structural forms using ductile membranes made of coated fabric. Using membrane structures, it is possible to construct large covered spaces relatively quickly and economically, and hence, they are being applied within various applications. The structures are light-weight, transparent, flexible in their application, economical and easy to maintain, and as such, their usage is being expanded. However, despite their prevalence, the standard for membrane material performance in terms of fire safety is still inadequate, and the development of membrane materials with excellent flame resistance performance is being demanded. This study determined flame resistance performance of architectural membranes, including PTFE, PVDF, PVF and ETFE film membranes, through flammability testing and incombustibility testing.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.572-572
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• 2012

Growth of metal oxides on graphene may lead to a better understanding of delicate effects of their growth habits on their underlying physics. The vanadium dioxide ($VO_2$) is well known for its metal-to-insulator transition accompanied by a reversible first order structural phase transition at 340 K. This transition makes $VO_2$ a potentially useful material for applications in electrical and optical devices. We report a successful growth of $VO_2$ nanostructures on a graphene substrate via a vapor-solid transport route. As-grown $VO_2$ nanostructures on graphene were systematically characterized by field emission scanning electron microscopy, x-ray diffraction, Raman spectroscopy, FT-IR spectroscopy and high resolution transmission electron microscopy. These results indicate that the strain between $VO_2$ and graphene layers may be easily controlled by the number of underlying graphene layer. We also found that the strain in-between $VO_2$ and graphene layer affected its metal-to-insulator transition characteristics. This study demonstrates a new way for synthesizing $VO_2$ in a desired phase on the transparent conducting graphene substrate and an easy pathway for controlling metal-to-insulator phase transition via strain.