• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.481-488
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• 2013

Nitric oxide ($NO_x$) formation characteristics in non-premixed diffusion flames of methane fuels have been investigated experimentally and numerically by adding 10% ammonia to the fuel stream, according to the variation of the oxygen ratio in the oxidizer with oxygen/carbon dioxide and oxygen/nitrogen mixtures. In an experiment of coflow jet flames, in the case of an oxidizer with oxygen/carbon dioxide, the $NO_x$ emission increased slightly as the oxygen ratio increased. On the other hand, in case of an oxygen/nitrogen oxidizer, the $NO_x$ emission was the maximum at an oxygen ratio of 0.7, and it exhibited non-monotonic behavior according to the oxygen ratio. Consequently, the $NO_x$ emission in the condition of oxyfuel combustion was overestimated as compared to that in the condition of conventional air combustion. To elucidate the characteristics of $NO_x$ formation for various oxidizer compositions, 1D and 2D numerical simulations have been conducted by adopting one kinetic mechanism. The result of 2D simulation for an oxidizer with oxygen/nitrogen well predicted the trend of experimentally measured $NO_x$ emissions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1119-1127
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• 2010

In this paper, the design and nonlinear simulation of a multistable electromagnetic microactuator, which provides four stable equilibrium positions within its operating range, have been discussed. Quadstable actuator motion has been made possible by using both X- and Y-directional bistable structures with snapping curved beams. Two pairs of the curved beams are attached to an inner frame in both X- and Y-directions to realize independent bistable behavior in each direction. For the actuation of the actuator at the micrometer scale, an electromagnetic actuation method in which Lorentz force is taken into consideration was used. By using this method, micrometer-stroke quadstability in a plane parallel to a substrate was possible. The feasibility of designing an actuator that can realize quadstable motion by using the electromagnetic actuation method has been thoroughly clarified by performing nonlinear static and dynamic analyses and electrothermal coupled-field analysis of the multistable microactuator.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.415-421
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• 2000

The effect of silica binder content on the mechanical properties of zircon shell mold was investigated. Content of binder silica sol to refractory powder in weight[$R_W$] was adjusted from 0.18 to 0.43. Sintering of the shell mold was carried out in the temperature range of $871^{\circ}C$ to $1400^{\circ}C$. Green strength of the shell mold at room temperature increased with increasing $R_W$ and sintering temperature up to $1300^{\circ}C$. However, the mold with $R_W$ of 0.43 that sintered at $1400^{\circ}C$ for 3 hours showed relatively low strength and large level of porosity. The mechanical behavior of the shells is supposed to attributed to the difference in thermal expansion coefficient between refractory powder and binder silica. The optimum value of $R_W$ for zircon-based shell molds was found to be 0.33.

• Elastomers and Composites
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• v.39 no.3
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• pp.217-227
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• 2004

A new thermotropic liquid crystalline polymer(TLCP) containing a triad aromatic ester type mesogenic unit and butylene terephthalate unit(BT) in the main chain was synthesized by polycondensation reaction. The TLCP synthesized showed nematic mesophasic behavior and its transition temperature from solid to mesophase was $260^{\circ}C$. The TLCP/PBT blends were prepared by in-situ polymerization in PBT solution and characterized by differential scanning calorimeter(DSC), thermogavimetric analyzer(TGA), scanning electron microscope(SEM), x-ray diffractometer(XRD), and dynamic mechanical thermal analyze, (DMTA). The blends showed well dispersed TLCP phases with domain sizes $0.05{\sim}0.2{\mu}m$ in the PBT matrix. As the increasing TLCP content from 5 to 20 wt%, ${\Delta}Hm$ values of pure PBT in the blend were increased because TLCP acts as a nucleating agent in the PBT matrix. The mechanical properties of the blends depended on the TLCP contents because the TLCP acted effectively as a reinforcing material in the PBT matrix. The blends showed good interfacial adhesion between the TLCP phase and PBT matrix.The blends prepared by in-situ polymerization showed higher mechanical properties and well dispersed TLCP domains than those of the blends prepared by melt blending.

• Advances in nano research
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• v.10 no.2
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• pp.115-128
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• 2021

In this article, free vibration behavior of electro-magneto-thermo sandwich Timoshenko beam made of porous core and Graphene Platelet Reinforced Composite (GPLRC) in a thermal environment is investigated. The governing equations of motion are derived by using the modified strain gradient theory for micro structures and Hamilton's principle. The magneto electro are under linear function along the thickness that contains magnetic and electric constant potentials and a cosine function. The effects of material length scale parameters, temperature change, various distributions of porous, different distributions of graphene platelets and thickness ratio on the natural frequency of Timoshenko beam are analyzed. The results show that an increase in aspect ratio, the temperature change, and the thickness of GPL leads to reduce the natural frequency; while vice versa for porous coefficient, volume fractions and length of GPL. Moreover, the effect of different size-dependent theories such as CT, MCST and MSGT on the natural frequency is investigated. It reveals that MSGT and CT have most and lowest values of natural frequency, respectively, because MSGT leads to increase the stiffness of micro Timoshenko sandwich beam by considering three material length scale parameters. It is seen that by increasing porosity coefficient, the natural frequency increases because both stiffness and mass matrices decreases, but the effect of reduction of mass matrix is more than stiffness matrix. Considering the piezo magneto-electric layers lead to enhance the stiffness of a micro beam, thus the natural frequency increases. It can be seen that with increasing of the value of WGPL, the stiffness of microbeam increases. As a result, the value of natural frequency enhances. It is shown that in hc/h = 0.7, the natural frequency for WGPL = 0.05 is 8% and 14% less than its for WGPL = 0.06 and WGPL = 0.07, respectively. The results show that with an increment in the length and width of GPLs, the natural frequency increases because the stiffness of micro structures enhances and vice versa for thickness of GPLs. It can be seen that the natural frequency for aGPL = 25 ㎛ and hc/h = 0.6 is 0.3% and 1% more than the one for aGPL = 5 ㎛ and aGPL = 1 ㎛, respectively.

• Membrane Journal
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• v.27 no.3
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• pp.216-225
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• 2017

Since the experimental proof of one-atom-thick graphene single layer from graphite in 2004, graphene, as a leading material opening two-dimensional world, has been tremendously investigated owing to its intrinsic extraordinary physical properties. Among many promising graphene applications, it is believed that membranes might be one of the first significant applications for graphene and its derivatives (e.g., graphene oxide). Recently, a number of simulation results and proof-of-concept experimental approaches towards graphene membranes reflect such positive prospects. Moreover, graphene and graphene oxide already show many outstanding intrinsic properties suitable for promising membrane platforms, such as the minimum membrane thickness, excellent mechanical strength, high chemical and thermal stability, and the ability to generate nanopores in the two-dimensional, rigid hexagonal lattices or to create slit-like nanochannels between adjacent sheets. In this paper, important theoretical and experimental developments in graphene or graphene oxide-based membranes for gas separation based on intrinsic properties of graphene and its derivatives will be discussed, emphasizing on transport behavior, membrane formation methods, and challenging issues for actual membrane applications.

• Applied Chemistry for Engineering
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• v.5 no.5
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• pp.889-898
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• 1994

Melt blends of copolyesterethylene(CPEE) and ethylene vinylacetate copolymer(EVA) with 15% vinylacetate content were prepared in the ratio of 0 to 100% CPEE with 10% interval for the purpose of obtaining useful biodegradable polymer system. Miscibility behavior of melt blend samples has been studied by observing the melting temperature change and cold crystallization temperature with differential scanning calorimetry. From the results of thermal analysis, it was shown that each 10% blend composition of CPEE and EVA had the partially miscibility. Useful compatibility has been observed in all blend composition except the samples of 50~80 % CPEE composition from the mechanical property study. Compatibility of these blend has been also observed with scanning electron microscopy. Biodegradability of CPEE/EVA blends has been evaluated by observing the change of specimen with Image analyzer before and after the inoculation with specific microorganism.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.99-104
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• 2003

TiN coated films show a good mechanical properties, high thermal properties and wear, erosion and corrosion resistance and are widely used as a coating materials in tools, ornaments, parts and semiconductors. In spite of these good properties, the fracture of TiN coated films occur during use. The fracture of TiN thin films is related to their microstructure. Especially, the life of TiN coated layer is related to the texture of the TiN films. One researcher suggested that the corrosion and erosion resistance of the TiN thin films is related to a uniform and dense structure of films. In this study, we studied the relationships between textures and friction coefficient, erosion and corrosion in TiN coated films. The flatness of (115) texture surface of TiN thin films is flatter than that of (111) texture surface. The friction coefficient of (115) texture surface of TiN thin films is similar with that of (111) texture surface. The wear resistance of (115) texture surface of TiN thin films is better than that of (111) texture surface. The erosion and corrosion resistance of (115) texture surface of TiN thin films is better than that of (111) torture surface. As well as texture, the wear, erosion and corrosion of TiN thin films has to consider defects such as pinholes, cracks, surface roughness and open columnar structure. The life of TiN coated products is influenced by the properties of wear, erosion, and corrosion resistance of TiN thin films and is related to texture of TiN coated films, density of pinholes and cracks, density of structure, and surface flatness.

• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.406-412
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• 2005

This work is to present a new synthesis of metallic glass (MG)/metallic glass (MG) composites using gas atomization and spark plasma sintering (SPS) processes. The MG powders of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ (CuA) and $Ni_{59}Zr_{15}Ti_{13}Nb_7Si_3Sn_2Al_1$(NiA) as atomized consist of fully amorphous phases and present a different thermal behavior; $T_g$ (glass transition temperature) and $T_x$ (crystallization temperature) are 716K and 765K for the Cu base powder, but 836K and 890K for the Ni base ones, respectively. SPS process was used to consolidate the mixture of each amorphous powder, being $CuA/10\%NiA\;and\;NiA/10\%CuA$ in weight. The resultant phases were Cu crystalline dispersed NiA matrix composites as well as NiA phase dispersed CuA matrix composites, depending on the SPS temperatures. Effect of the second phases embedded in the MG matrix was discussed on the micro-structure and mechanical properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1671-1676
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• 2015

A unique crystallization behavior of poly(L-lactide)(PLLA)/poly(D-lactide)(PDLA) stereocomplex(SC) was observed when a PLLA/PDLA blend was subjected to the specific melting conditions. Therefore, we tried to blend PLLA and PDLA at overall composition to form PLA stereocomplexes. Moreover, impact modifier and reinforcement materials such as talc and glass fiber added to enhance the mechanical and thermal properties such as impact strength and heat distortion temperature(HDT). As a result, we got one representative result, one composite recipe with HDT $115^{\circ}C$. For more economic technology, we tried to blend PLLA and Polypropylene at overall composition and we got another representative result which could be applied to current PP/talc composites and ABS materials. The core technology of this might be the well dispersion of glass fibers into the matrix resin such as PP, PLLA and impact strength modifier.