• Journal of the Korean Wood Science and Technology
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• v.45 no.3
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• pp.268-277
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• 2017

In this study, lignocellulose nanofibrils (LCNFs) were prepared from Pussy willow wood powder by disk-milling after pretreatment using the cosolvent of 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and N,N-dimethylformamide (DMF) with different mixing ratios for different time. All pretreated samples showed native cellulose I polymorph and cellulose crystallinity was lowest when cosolvent of DMF with 30% [EMIM]Ac was used. Average crystallite size of raw material and the pretreated product by MDF and its cosolvent with 10% [EMIM]Ac was found to be about 3.2 nm and decreased with increasing pretreatment time at the DMF cosolvent with 30% [EMIM]Ac. Defibrillation efficiency was improved by loosening wood cell wall structure by the pretreatment using co-solvent system of [EMIM]Ac and DMF.

• Journal of the Korean Wood Science and Technology
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• v.29 no.1
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• pp.43-51
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• 2001

When percentages of the component of raw lacquer were changed by adding each components that is urushiol, polysaccharide and glycoprotein, the physical properties of refined lacquer were changed and the period of refining also were changed. When polysaccharide component extracted from raw lacquer was added in raw lacquer, the period of refining was shortened about 1/3 times and this refined lacquer film was dried faster than the refined lacquer which was not added any other components. When urushiol extracted from raw lacquer was added in raw lacquer, the transparency of dried film was improved. A case of Guizhoushang was improved of the tensile strength of dried film. When both urushiol and polysaccharide were added in raw lacquer, the drying time of refined lacquer was shortened and the tensile strength of them also was improved.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.155-160
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• 2002

Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties. It was also highlighted as the materials of frontier industry because strength, heat-resistant, corrosion-resistant, wear-resistant were superiored. In this study the strength properties of $Al_{18}B_4O_{33}/AC4CH$ were represented mixing the binder of $Al_2O_3$ and $TiO_2$. It was also fabricated by squeeze casting. $Al_{18}B_4O_{33}/AC4CH$ was fabricated at the melt temperature of $760^{\circ}C$ the perform temperature of $700^{\circ}C$ and mold temperature of $200^{\circ}C$ under the pressure of 83.4MPa and observed SEM. Fatigue crack growth rate tests on compact tension specimen(half-size) of thickness 12.5mm were conducted by using sinusoidal waveform. Compact tension specimens(half-size) were used and fatigue crack growth rate da/dN and stress intensity factor range ${\Delta}K$ were analyzed concerning to the R value of 0.1 and 0.05. In order to find out the value of ${\Delta}K$, load amplitude constant method was applied by the standard fatigue testing method describes in ASTM E647-95a. As the results of this study, Fatigue crack growth rate increased with in creasing the load ratio, Consequently, At equivalent stress intensity factors, the fatigue crack growth rates in MMC were faster than those of AC4CH alloy. then the fatigue life and the fatigue crack growth rate was investigated using scanning election microscopy(SEM)

• International Journal of Highway Engineering
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• v.18 no.3
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• pp.67-74
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• 2016

PURPOSES : This study evaluated the field applicability and laboratory performance of glass fiber-reinforced asphalt (GFRA) mixtures. METHODS : The general hot-mix asphalt (HMA) and GFRA mixtures were paved in five sites, including three national highways, one express highway, and an arterial road, to evaluate field applicability and durability. The plant mixing and construction method for the GFRA were similar to those for the general HMA. The lab performances of the field samples were relatively compared through the mechanical measures from the Marshall stability, indirect tensile strength, and dynamic stability. The field performance was surveyed after a year. RESULTS : The lab tests verified the superior lab performances of the GFRA compared to the general HMA. The Marshall stability of the GFRA increased for about 128% of the general HMA. The indirect tensile strength of the GFRA was 115% greater than that of the general HMA. The dynamic stability of the GFRA resulted in 16,180 reps/mm, which indicated that high rut resistance may be expected. No noticeable defects, such as cracks or deformation, were observed for the GFRA sections after a year. CONCLUSIONS : The lab tests and field survey for the five GFRA sites resulted in superior performances compared to the general HMA. The relatively low-cost GFRA, which required no pre-processing procedures, such as polymer modification, may be a promising alternative to the polymer-modified asphalt mixtures. The long-term performance will be verified by the superior field durability of the GFRA in the near future.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.368-373
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• 2009

A human tissue mimicking phantom is constructed to assess the performance of a medical ultrasound elasticity imaging system. In a human body, the tumor or cancer is stiffer than its surrounding normal tissue. A technique fur imaging the elasticity of such a tissue is referred to as elastography. Homogeneous elasticity phantoms with differing Young's moduli are constructed using a plastic hardener and softener to simulate the mechanical characteristics of a diseased human tissue. The Young's modulus of the fabricated homogeneous phantom materials were measured from 11.1 to 79.6 kPa depending on the mixing ratio of the amount of the hardener to that of the softener. An ultrasound lesion mimicking phantom was made of these materials, and ultrasound elasticity imaging was performed on it. It is confirmed in this paper that the fabricated plastic-based elasticity phantom is useful in representing the elastic characteristics of a human tissue.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.1
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• pp.1-8
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• 2013

This study will not only prove experimental dynamic properties which are classified to slump, compressive strength, tensile strength, flexure strength and toughness granite soil concrete with a fine aggregate of granite soil and blast-furnace cement and polypropylene fiber over 45 mm, but also establish a basic data in order to use environment-friendly pavement through prove useful pavement mixed with granite and polypropylene (PP) fiber which is a kind of material to prevent a dry shrinkage clack, a partial destruction and useful and light. The value of slump test was gradually increased by PP fiber volume 3 $kgf/m^3$, but compressive strength took a sudden turn for the worse from 5 $kgf/m^3$. The compressive strength indicated a range of 13.72~18.35 MPa. On the contrary to compressive strength, the tensile strength showed to decrease with rising PP fiber volume, and the tensile strength indicated a range of 1.43~1.64 MPa. The tensile strength was stronger about 2~15 % in case of mixing with PP fiber volume than normal concrete. The flexural strength indicated a range of 2.76~3.41 MPa. The flexural strength was stronger about 20 % in case of PP fiber volume 0 $kg/m^3$ than PP fiber volume 9 $kg/m^3$. The toughness indicated a range of 0~25.46 $N{\cdot}mm$ and increased proportionally with PP fiber volume. The toughness was stronger about 8.3 times in case of PP fiber volume 9 $kg/m^3$ than PP fiber volume 1 $kg/m^3$. The pavement with PP fiber volume over such a fixed quantity in the park roads and walkways can have a effect to prevent not only resistance against clack but also rip off failures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3403-3409
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• 2014

Hot-firing tests were carried out using a mixing head with 19 swirl coaxial injectors and a combustion chamber with internal cooling channels. The propellants of liquid oxygen and kerosene(Jet A-1) were burned in a range of chamber pressures (59~82 bar) and mixture ratios (2.0~3.0). The temperature of water used as the cooling fluid was measured at the inlet and outlet of the cooling channels, and the heat flux was calculated. The aim of this study was to examine the effect of combustion instability on heat transfer in a subscale thrust chamber, and detect the temperature variation of cooling water. During several hot-firing tests, combustion instability was encountered which caused a 5~20% increase in heat flux. The peak heat flux took place in the initial stages of combustion instability.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.2
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• pp.92-98
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• 2015

The physical effect induced by acoustic cavitation was investigated to accumulate basic data for the design of ultrasonic soil washing processes using aluminum foil erosion tests. A square aluminum foil was placed on the glass beads in the pyrex vessel submerged in the sonoreactor equipped with a 36 kHz ultrasound transducer module at the bottom. Cavitational erosion of foils was quantitatively analyzed for various glass bead diameter conditions (1, 2, and 4 mm), glass bead height conditions (5, 10, 15, and 20 mm), and water height conditions (5, 10, 15, and 20 mm). It was found that aluminum foil erosion significantly increased as the glass bead diameter increased and water height over the glass bead increased due to less attenuation of ultrasound and the optimization of sound field for cavitation. Moreover mechanical mixing was suggested to move constantly particles to the bottom area where the acoustic cavitation occurs most violently. It was because aluminium foil erosion by ultrasound transmitted through glass beads was relatively too weak.

• Elastomers and Composites
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• v.42 no.2
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• pp.86-92
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• 2007

A few of polytetrafluoroethylene(PTFE) membranes and PTFE fine powders were analyzed to chooce an optimum resin. The bi-axial stretching process was developed to set up the foundation of the preparation process and control the pore size and porosity of PTFE membrane. The pretreatment of PTFE fine powder used in the preparation process for PTFE was needed. The mixing of additives, the ripening of mixture, paste extrusion process of ripening powder, calendering process and the bi-axial process were conducted for controlling pore size, porosity and thckness of membrane. The aftertreatment which strengthened the mechanical properties was necessary. The control of pore size and porosity of the membrane were determined. The ratio of PTFE fine powder and additives at the paste extrusion process, the ripening time, the ripening temperature and the parameters of temperature and pressure at the paste extrusion process were optimized.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.467-471
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• 2010

Composites of ceramic powders and an elastomer-based matrix were prepared by mixing $CaCO_3$ powders with polyethylene and polypropylene elastomers, and their mechanical and sound insulation properties were measured. $CaCO_3$ powders with 0.7 ${\mu}m$ and 35 ${\mu}m$ particle size were added to elastomers up to 80 wt%. Scanning electron microscopy photographs showed uniform distribution of the $CaCO_3$ powders in the matrix. While density and surface hardness increased, melt index, tensile strength and elongation of the composites decreased as the amount of added $CaCO_3$ powders increased. As more $CaCO_3$ powders were added sound transmission loss of the composites increased owing to the increase of density. Addition of 0.7 ${\mu}m$ sized $CaCO_3$ powders resulted in a slightly higher transmission loss than the addition of 35 ${\mu}m$ sized powders because of the increased interface area between the elastomer matrix and the $CaCO_3$ powders. Composites with a polyethylene matrix showed higher transmission loss than those with a polypropylene matrix because the tensile strength and hardness of the polyethylene-based composites were low and their elongation was high.