• Proceedings of the KSR Conference
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• 2011.10a
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• pp.3160-3165
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• 2011

The track and bridge interaction should be considered for the safety check of railway bridge design as the longitudinal forces transmitted to rail and bridge are changed by longitudinal stiffness of bridge system. The longitudinal stiffness of bridge structures is determined by the magnitude of the ballast resistance, the expansion length of superstructure, and longitudinal stiffness of substructure including pier and foundations. In this study, the main factors affect on the longitudinal rail forces are discussed and the computational parametric analysis of rail forces considering rail-bridge interactions. And the required range of stiffness of sub-structures and span length for the assurance of safety of CWR(continuous welded rail) track is suggested.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.3
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• pp.1-7
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• 2011

Active brazing of ceramic to metal is reviewed in this paper. As one of the key aspect in joint techniques, active brazing has been developed to simplify the manufacturing procedure of brazed joints between ceramic and metal. The active filler metal includes Ag-Cu-Ti series, Cu-Ti series, Co-Ti series and so on. The active filler metal which supplies the chemical bonds between ceramic and metal, enhances the wetting of filler metal on ceramic surface and eliminates the need for metallization treatments. The residual stress caused by difference of coefficient of thermal expansion between ceramic and metal, holds a direct influence on the bonding strength and even results in a fracture. Good joints of ceramic to metal promote the miniaturization and simplicity of electronic components with multifunction.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.175-183
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• 2000

The internal residual stresses within the multilayered structure with shan interface induced by the difference in thermal expansion coefficient between the materials of adjacent layers often provide the source of failure such as delamination of interfaces and etc. Recent development of the multilayered structure with functionally graded interface would be the solution to prevent this kind of failure. However a systematic thermo-mechanical analysis is needed fur the customized structural design of multilayered structure. In this study, theoretical model for the thermo-mechanical analysis is developed for multilayered structures of the Al-$SiC_p$ functionally graded composite for electronic packaging. The evolution of curvature and internal stresses in response to temperature variations is presented for the different combinations of geometry. The resultant analytical solutions are used for the optimal design of the multilayered structures with functionally graded interface as well as with sharp interface.

• Journal of the Korean Ceramic Society
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• v.16 no.3
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• pp.169-177
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• 1979

The effect of apparent porosity of the fired ceramics, metallizing temperature, and metallizing mixtures on the bond strength in metal-to-ceramic seals was investigated. Three different metallizing compounds were metallized on dense alumina bodies at 1300~$1500^{\circ}C$ in dry hydrogen atmosphere. Bond strength between metal and alumina body was measured by means of nstron test machine. The greater bond strength was observed as the apparent porosity and metallizing temperature was increased. This work indicated that the glassy phase in metallizing mixture, having had sufficient fluidity to migrate into the alumina body, reacted with alumina and thereby forming strong metal-ceramic interface bond. It also showed that the glassy phase having higher thermal expansion cofficient than molybdenum might contribute to the strong bond formation by providing compressive stress around the molybdenum particle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.25-31
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• 2001

The theoretical modeling to predict the modulus of elasticity by the shape memory effect of dispersed particles in a metal matrix composite was studied. The modeling approach is based on the Eshelbys equivalent inclusion method and Mori-Tanakas mean field theory. The calculation was performed on the TiNi particle dispersed Al metal matrix composites(PDMMC) with varying volume fractions and prestrains of the particle. It was found that the prestrain has no effect on the Yonugs modulus of PDMMC but the volume fraction does affects it. This approach has an advantage of definite control of Youngs modulus in PDMMCs.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.235-243
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• 1998

For motor operation at low speeds and loads, torque pulsation by the cogging torque is often a source of vibration and control difficulty. In this paper, the magnetic field of a motor is calculated by finite element method. The periodic cogging torque is determined using Maxwell stress method and time stepping method, and then decomposed using fourier series expansion, The purpose of this paper is to characterize design parameters on the cogging torque and to design a permanent magnet motor with a cogging torque less vulnerable to vibration, without sacrificing the motor performance. The design parameters include stator slot width, permanent magnet slot width, airgap length and magnetization direction. A new design with a less populated frequency spectrum of the cogging torque is proposed after characterizing individual effect of design parameters. Magnet pole edge shaping, by gradually increasing the cogging torque with reduced higher harmonics.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.96-101
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• 2011

Under extreme test or operation condition, refrigerator endures complicated stresses state and thermal bowing deformation arises on the sidewall. Shelf rails designed in the inner case provide increased surface area to permit expansion without bowing, and also increase structural rigidity to resist bowing. In this study, we designed six different shelf patterns of refrigerator model and studied the bead on refrigerator deformation using finite element method (FEM). Analysis result shows that increasing the numbers of beads properly in refrigerator is more helpful to reduce thermal bowing deformation. In addition, the beads would decrease stress on refrigerator sidewall. However, vertical beads have no effect to reduce thermal deformation of the bowing.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.173-180
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• 2004

This paper presents the effect of varying boundary conditions such as ground subsidence, internal pressure and temperature variation for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function incorporating with von-Mises failure criteria is used in order to estimate the probability of failure mainly associated with three cases of ground subsidence. Using stresses on the buried pipelines, we estimate the probability of pipelines with von-Mises failure criterion. The effects of varying random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the pipeline crossing ground subsidence regions which have different soil properties.

• Macromolecular Research
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• v.9 no.1
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• pp.1-19
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• 2001

Poly(p-phenylene pyromellitimide) and poly(4,4'-biphenylene pyromellitimide) are representatives of fully rod-like polyimides. Their structure and properties in thin films are reviewed. The polymers exhibit some excellent properties such as high molecular packing coefficient, high mechanical modulus, and low thermal expansion coefficient, and low interfacial stress, so that they are very attractive to both industry and academia. However, these polymers are very brittle and thus practically useless. Some chemical modifications to improve such drawback with a little sacrifice of the high modulus are described: i) incorporation of short side groups into the polymer backbone and ii) insertion of proper linkages into the polymer backbone.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.197-202
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• 2005

This study started to confirm and prove for the applicability of the dry-process waterproofing system to cover the defects of the wet-process waterproofing system according to weather circumstance, foundation condition and maintenance, etc. This process has triple combined waterproofing system using asphalt sheet, metal sheet, engineering plastic film. It is not influenced by the concrete's crack as the foundation of the roof according to the movement of the building because the waterproofing system is designed for maintaining good quality by absorbing the stress of contraction and expansion that is occurred by the variation of temperature. Ali components used in this process can be recycled environmentally. The superiority of this process proved and reconfirmed through with the investigation of about 130 fields, around 30,000nf for two years.