• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.136-142
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• 2018

Additive manufacturing process technology, known as the 3D printing process, is expanding its utilization from simple model realization to commercialized part production based on continuous material development. Recently, research and development have been actively carried out to fabricate lightweight and high-strength parts using polymers, such as polyamide (polyamide), which is a high-strength engineering plastic material. In this study, the Izod impact characteristics were analyzed for polyamide 12 (PA12) materials. For the specimen production, selective laser sintering process technology, which has excellent mechanical properties of finished products, was applied. In addition, PA12 and glass bead reinforced PA12 materials were produced. The specimens were classified according to the production direction on the production platform, and each specimen was subjected to an Izod test at test temperatures of $-25^{\circ}C$, $25^{\circ}C$, and $60^{\circ}C$. As a result, the impact strength of PA12 and glass bead-reinforced PA12 of vertical direction specimens were 48.8% and 16.3% lower than those of the parallel specimens at a $25^{\circ}C$ test temperature and the impact strength of parallel specimens was improved by 46.5% and 20.4% at a test temperature of $60^{\circ}C$ compared to that at $-25^{\circ}C$.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.37-46
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• 2017

PURPOSES : A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC base. METHODS : This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and $1.1l/m^2$ to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and $40^{\circ}C$. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed. RESULTS : The test results indicated that the optimal application rate of RSC-4 and BD-Coat were $0.8l/m^2$, $0.9l/m^2$, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and $20^{\circ}C$, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of $40^{\circ}C$. CONCLUSIONS : This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

• Journal of Surface Science and Engineering
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• v.41 no.5
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• pp.245-253
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• 2008

The porous metal material is used for injection metal mold with a great deal of gas production because it makes plenty of gas exhausted through pores formed in the metal mold. A canning HIP method was conventionally used for manufacturing of porous metals, but because of difficulty of process control and high cost of production its application was limited. In this experiment, porous metal mold material was produced by an enhanced vacuum sintering method with simply controlled and economical process and porosities/mechanical properties with variation of sintering temperature and duration time during vacuum sintering were studied. As a result, quality goods were obtained at optimized conditions as follows: sintering temperature of $1230^{\circ}C$, duration time of 2 hr and showed superior properties in wear loss and thermal conductivity and the same properties in hardness, TRS (Transverse Rupture Strength), and thermal expansion coefficient in comparison with those under canning HIP.

• Corrosion Science and Technology
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• v.12 no.5
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• pp.233-238
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• 2013

In the case of casting materials or ductile materials for marine equipment, it is common to employ a surface modification for achieving cost reduction and improvement in strength. In particular, aluminium bronze ALBC3 exhibits excellent corrosion resistance, and thus widely used for marine application. However, application of the material under high-velocity seawater flow may induce electrochemical corrosion damage and physical damage such as cavitation erosion, leading to shorter service life of equipment. In this study, surface modification was carried out on ALBC3 alloy for different shot peening stand-off distances, and the physical hardness and electrochemical characteristics before and after modification were investigated. The results in each case showed the hardness increase in comparison with non-peened specimen, and the maximum hardness improvement(50 %) was found in 10 cm of shot-peening stand-off distance. It is observed that the electrochemical characteristics were irrelevant to application of shot peening.

• Korean Journal of Materials Research
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• v.19 no.9
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• pp.473-480
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• 2009

In order to provide the mechanism of nozzle clogging, recovered nozzles for high strength steel grade were examined carefully after continuous casting. The thickness of clogged material in SEN is increased in the following order: from the bottom to the top of the nozzle, upper part of slag line, and the pouring hole. Nozzle clogging material begins to form due the adhesion of metal to nozzle wall, the decarburization, and reduction of oxide in the refractory by Al and Ti in the melt. The reduction of oxide in the refractory by Al and Ti improves the wettability of the melt on the refractory and forms a thin Al-Ti-O layer. Metal containing micro alumina inclusions is solidified on the Al-Ti-O layer, and the solid layer grows due to the heat evolution through the nozzle wall. Thermodynamic calculation has been made for the related reactions. The effect of superheat to the nozzle clogging is discussed on ultra low carbon steel and low carbon steel.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.10a
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• pp.5-21
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• 2005

Urbanization rates of population range from about 1% in the developed countries to about 4% in developing countries. For a global population that may reach 10 billion within the next 40 years, pressure has arisen for an increase in the large-scale use of wastes and byproducts in construction. Ironically, most of the wastes that need to be recycled are generated in large cities where the need for constructed facilities to serve large population is high. Waste and recycled materials (WRM) that are used in construction are required to satisfy material strength, durability and contaminant teachability requirements. These materials exhibit a wide variety of characteristics owing to the diversity of industrial processes through which they are produced. Several laboratory-based investigations have been conducted to assess the pollution potential and load bearing capacity of materials such as petroleum-contaminated soils, coal combustion ash, flue-gas desulphurization gypsum and foundry sand. For full-scale systems, although environmental pollution potential and structural integrity of constructed facilities that incorporate WRM are interrelated, comprehensive schemes have not been developed for integrated assessment of the relevant field-scale performance factors. In this presentation, a framework for such an assessment is proposed and presented in the form of a flowchart. The proposed scheme enables economic, environmental, worker safety and engineering factors to be addressed in a number of sequential steps. Quantitative methods and test protocols that have been developed can be incorporated into the proposed scheme for assessing the feasibility of using WRM as partial or full substitutes for earthen highway materials in the field.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.38 no.4 s.117
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• pp.53-60
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• 2006

Paper materials for long term conservation suffer slowly mechanical and chemical deterioration, the extent of which may depend upon their conservation environment. Those deterioration includes discoloring, low moisture content, acidification, and brittleness. To slow deterioration, washing treatment, deacidification, and polymer reinforcement on paper materials are usually used. One easy and simple method of fixing low moisture content and acidification was an washing method, and we used both distilled and alkali water in washing method in this study. Alkali water is electrolyzed cathode water of high pH, and has no alkali metal ions in it. Experiment showed that washing treatment with both distilled and alkali water gave improvement in raising moisture content, pH, and mechanical strength of paper materials even after severe accelerated aging test. Advantageous effect of alkali water over distilled water on preventing deterioation was also shown clearly.

• Journal of Korea Foundry Society
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• v.32 no.3
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• pp.127-132
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• 2012

Al-Zn-Mg alloys, being high strength aluminum alloys, have attracted attention as a material of automobile parts that require higher mechanical properties and lightness. Automobile parts with complex shapes are manufactured by low-priced casting method, but Al-Zn-Mg alloys are difficult to cast because of its poor hot cracking, feeding, and fluidity. Thus fluidity experiments on Al-Zn-Mg alloys were conducted for the castability evaluation. The effects of Mg and Zn, representative elements of Al-Zn-Mg alloys, on fluidity were observed. Spiral mold was used for fluidity experiments and the lengths of solidified specimens were measured after melting and gravity casting. Correlation between microstructures and fluidity length based on the alloy composition was considered. According to the experimental results, as the amount of Mg and Zn increased, fluidity decreased. Also, it was confirmed that fluidity change by the variation of Mg composition was greater than that of Zn.

• Transactions of Materials Processing
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• v.27 no.2
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• pp.93-99
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• 2018

An analytical solution for the tensile ductility in porous ductile materials was derived based on an Irwin's approach of the elastic-plastic deformation in fracture mechanics. This was in good agreement with the experimental results of a tensile ductility in a sintered pure Al, and could solve the discrepancies in the Brown and Embury, or the McClintock models. This model was also offered as an advanced analytical solution considering the effect of stress triaxiality of pore tip in addition to pore interactions, material properties of matrix, and local deformation effect around pore. The evaluation of an analytical solution in the sintered pure Al powder compacts showed that the tensile ductility depends not only on the volume fraction of pores, but also on the pore size and on the mechanical properties of the matrix. The tensile ductility of the sintered pure Al compacts decreased rapidly with the increasing of a pore volume fraction, despite of the excellent tensile ductility of the matrix. This significant decrease in the tensile ductility was mainly attributed to the low yield strength of the matrix and small pore size. Particularly, the effects of the large radius and high volume fraction of the pore on the tensile ductility in Al-Form, were thus reasonably predicted by this analytical equation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.865-870
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• 2012

CFRP of the advanced composite materials as structure materials for vehicles has a widely application in lightweight structural materials of air planes, ships and automobiles because of high strength and stiffness compared with conventional materials. This study is to investigate the energy absorption characteristics and collapse mode of CFRP single and double hat shaped structural member under the axial static collapse test. The CFRP single and double hat shaped structural members stacked at different angles (${\pm}15^{\circ}$, ${\pm}45^{\circ}$, ${\pm}90^{\circ}$, $90^{\circ}/0^{\circ}$ and $0^{\circ}/90^{\circ}$ where the direction on $0^{\circ}$ coincides with the axis of the member). The axial static collapse tests were carried out for each member. Collapse mode and energy absorption characteristics of the each member were analyzed.