• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.3
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• pp.47-57
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• 2011

All solid rocket propellants are divided in two basic classes according to chemical state: homogeneous(double base) and heterogeneous (composite). Today, composite propellants are extensively used as power sources covering the range from gas generators and small rocket systems to large launch vehicles in space programs. The development of composite rocket propellants in the past was mainly directed to thermoset polymers. But, the thermoset composite propellants have the complication in formulation and fabricating process to adapt to rocket system requirements. In contrast to the thermoset propellant, the PVC plastisols composite propellants have the advantages in the view of loss in manufacturing process, low cost of raw material, and stability of the handling process even though moderate ballistic and mechanical properties. It is predicted that the application field of this class will be used more widely than any other classes.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.102-108
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• 2018

The objective of this study is to develop the mechanical properties of an AlSiCu aluminum alloy using the two-step solution heat treatment. The microstructure of the gravity casting specimen represents a typical dendrite structure with a secondary dendrite arm spacing (SDAS) of 40 um. In addition to the Al matrix, a large amount of coarsen eutectic Si phase, $Al_2Cu$ intermetallic phase, and Fe-rich phases is generated. The eutectic Si phases are fragmented and globularized with the solution heat treatment. The $Al_2Cu$ intermetallic phase is also resolutionized into the Al matrix. The $2^{nd}$ solution temperature at $525^{\circ}C$ may be an optimal condition to enhance the mechanical properties of the AlSiCu aluminum alloy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.776-781
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• 2017

In this study, we investigated the effect of electrode pattern design on the thermal shock resistance and temperature uniformity of a ceramic heater. A cordierite substrate with a low thermal expansion coefficient was fabricated by tape casting, and a tungsten electrode was printed and used as a heating element. The temperature distribution of the ceramic heater was calculated by a finite-element method (FEM) by considering various electrode patterns, and the tensile stress distribution due to the thermal stress was calculated. In the electrode pattern with a single-line width, the central part of the ceramic heater was heated to the maximum temperature, and the position of the ceramic heater having a double-line width was changed to the maximum temperature, depending on the position of the minimum line width pattern. The highest tensile stress was found along the edges of the ceramic heater. The temperature gradient at the edge determined the tensile stress intensity. The smallest tensile stress was observed for electrode pattern D, which was expected to be advantageous in resisting thermal shock failures in ceramic heaters.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.5
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• pp.197-206
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• 2017

The microstructure of a high-carbon and high-chromium cast steel (HK700) for cold-work die inserts was analyzed by advanced scanning electron microscopy. A continuous network of primary $M_7C_3$ carbide was developed among austenitic matrix after casting. A small amount of $M_2C$ was added to the carbide network owing to the enrichment of Mo and W during the solidification. After quenching in which the austenitization was performed at $1030^{\circ}C$ and double tempering at $520^{\circ}C$, the network structure of $M_7C_3$ was preserved while most of the matrix was transformed to martensite because of additional carbide precipitation. The $M_2C$ in the as-cast microstructure was also transformed to $M_6C$ due to its instability. The continuous network of coarse carbides owing to the absence of hot-working had little influence on the hardness after quenching and tempering, whereas it resulted in severe brittleness upon flexural loading.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.388-390
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• 1994

We are familiar with the holography in these days. For making holography the coherent sources like LASER are used in many fields. But coherent holography has many problems. Coherent holography needs many instrument for practical use like 3-D TV case. In solving the problem we use the non-coherent source. Nowadays many methods like conoscopic holo graphy using anisotropic crystal, shadow casting and interferometric systems are suggested. In this paper we make the hologram using the triangular interferometric systems. [1],[2],[3],[4]. We explain the afocal and double-afocal system which consists of the triangular interferometric system. The holography made in one point and two point cases is imaged on CCD camera and we handle the image data digitally for the reconstruction efficiently. In reconstructing the hologram the Fraunhofer diffraction theory is used. We adopt the rectangular aperture for the convenience of calculation. In the future we must reconstruct the perfect 3-Dimensional object by optical method. For this, we have many problems like resolution problem. We must solve these problem for perfect reconstruction.

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.440-447
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• 2011

To improving the mechanical properties of Mg alloys at high temperature, we investigated the mechanical properties at high temperature and the change of microstructure of Mg-6 wt%Zn-0.4 wt%Mn and Mg-6 wt%Zn-0.4 wt%Mn-1 wt%Ag alloys on age treatment that have a stable MgZn phase at high temperature and $AgMg_4$ improving yield stress. In order to predict thermodynamic data of Mg alloys, a phase diagram and precipitation phase were calculated using a thermodynamic program, and it was confirmed that the MgZn and $AgMg_4$ phase existed as main precipitation in this alloys. The experimental data examined using DSC and XRD were comparable with the calculated data for reliability. In order to analysis the microstructure and precipitate phase during aging treatment, it was measured by SEM/EDS and TEM. Lastly, mechanical properties of the MgZn and $AgMg_4$ phase were measured by a tensile test at high temperature.

• Journal of the Korea Organic Resources Recycling Association
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• v.20 no.4
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• pp.75-85
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• 2012

This study was investigated to develop an alternative medium for the cultivation of oyster mushrooms. The cultivation characteristics for major cultivated varieties of oyster mushrooms were campared with the food waste medium. In addition, water control & a gap formation of food waste is being pointed out as a problem of the medium material. Therefore, certain amounts of earthworm casting were supplied to the food waste medium to overcome the water and compaction phenomenon. This study investigated the use of the total 6 cultivars of oyster mushrooms, the Suhan(PL.1), Chiak No. 5(PL.2), Chiak No. 7(PL.3), Samgu No. 5(PL.4), Samgu No. 8(PL.5), Jangan No. 5(PL.6). In terms of medium, the optimum growth of the mycelium of the oyster mushroom was observed in the beet pulp medium but in food waste, the mycelium's growth was observed as insufficient in the bulk of cultivars. The Jangan No. 5(PL.6) was superior to other cultivars relative to the mycelium's growth. The optimum concentration of earthworm casting added the foodwaste medium was 30%. When Jangan No. 5(PL.6) was incubated in the foodwaste meidum containing 30% earthworm casting, the early days to germination were long, almost double the amount of time than that of the beet pulp medium. However, it was found that the fruit body size was larger than that of the beet pulp by up to 20.5%, and the length of the fruit body was up to 6.2% longer than that of the beet plup. The total yields increased by 60.5%. The analysis results of the oyster mushroom's nutritional contents cultured using the food waste medium, shows that the protein, vitamin A and vitamin E increased 70.6%, 2.4%, 0.8% respectively, the fat decreased by 12.6% and the oleic acid increased in a very small amount compared to that of the beet pulp medium.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.26-32
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• 2020

Concrete recycling is becoming mandatory rather selective due to depletion of constructional materials and increase of concrete waste. Studies on recycling concrete are conducted in various point of view for long time. However, standard or guideline of many countries for the application of recycled aggregate concrete(RAC) has restrictions such as low replacement rate of coarse aggregate and no fine aggregate allowed due to inferior material properties of recycled aggregate. This study intends to figure out the feasibility of casting natural aggregate concrete(NAC) and RAC separately in a structural member. In making RAC, replacement rate of coarse aggregate was 50, 100% in RAC and treatment of interface of two concretes is introduced. RAC treatment of recycled aggregate or inclusion of additives was not done as it can increase embodied energy of concrete work. Double-shear test with uniformly distributed loading was adopted to evaluate shear strength at the interface of two concretes. After curing it was hard to distinguish interface of two concretes. Experimental result revealed that specimen with higher replacement rate showed higher shear-to-compressive strength ratio, which is possibly attributed to coarse aggregate size and roughness of sheared section. Further study on the effect of various parameters is required and subsequent research activity is on-going.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.773-780
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• 2011

In this study, thermal stress analysis are carried out considering material properties, curing condition, ambient temperature, and casting date of the mass concrete placed in bottom slab and side wall of the in-ground type LNG tank as a super massive structure. Also, based on the numerical results, cracking possibility is predicted and counter measures to prevent the cracking are proposed. For the tasks, two optimum mix proportions were selected. From the results of the thermal stress analysis, the through crack index of 1.2 was satisfied for separately caste concrete lots except for the bottom slab caste in 2 separate sequences. For the double caste bottom slab, it is necessary introduce counter measures such as pre-cooling prior to the site construction. Also, another crack preventive measure is to lower the initial casting temperature by $25^{\circ}C$ or less to satisfy 1.2 through crack index criterion. In the $1^{st}$ and $2^{nd}$ caste bottom slab, the surface crack index was over 1.2. Therefore, the surface cracks can be controlled by implementing the curing conditions proposed in this study. Since the side wall's surface crack index was over 1.0, it is safe to assume that the counter preventive measures can control width and number of cracks.

• International Journal of Concrete Structures and Materials
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• v.8 no.1
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• pp.83-97
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• 2014

This paper presents the results of an investigation aimed at developing reinforced concrete beams consisting of precast permanent U-shaped reinforced mortar forms filled with different types of core materials to be used as a viable alternative to the conventional reinforced concrete beam. To accomplish this objective, an experimental program was conducted and theoretical model was adopted. The experimental program comprised casting and testing of thirty beams of total dimensions $300{\times}150{\times}2,000mm$ consisting of permanent precast U-shaped reinforced mortar forms of thickness 25 mm filled with the core material. Three additional typical reinforced concrete beams of the same total dimensions were also cast to serve as control specimens. Two types of single-layer and double-layers steel meshes were used to reinforce the permanent U-shaped forms; namely welded wire mesh and X8 expanded steel mesh. Three types of core materials were investigated: conventional concrete, autoclaved aerated lightweight concrete brick, and recycled concrete. Two types of shear connections between the precast permanent reinforced mortar form and the core material were investigated namely; adhesive bonding layer between the two surfaces, and mechanical shear connectors. The test specimens were tested as simple beams under three-point loadings on a span of 1,800 mm. The behavior of the beams incorporating the permanent forms was compared to that of the control beams. The experimental results showed that better crack resistance, high serviceability and ultimate loads, and good energy absorption could be achieved by using the proposed beams which verifies the validity of using the proposed system. The theoretical results compared well with the experimental ones.