• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1999.04a
• /
• pp.5-5
• /
• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.8 no.3
• /
• pp.269-275
• /
• 2020

In this study, flexural tests of precast concrete panels according to the thickness of cross-sectional and the with or not of reinforcement were carried out in order to develop and assess of a lightweight precast concrete panel using ultra high performance concrete. For the test, four panels were fabricated, and consisted of one normal concrete panel and three ultra high performance concrete panels. As a test result, it was found that the plain precast panel using ultra high performance concrete had a lower flexural performance than the reinforced normal concrete panel, regardless of the cross-sectional size. The flexural performance of the hollow-sectional precast panel applying ultra high performance concrete, is improved by 150% compared to that of the reinforced normal concrete panel. That is, through additional performance verification and optimization of the cross-sectional design of the panel, the ultra high performance concrete precast panel can be made lighter. Also, the practical use of lightweight precast panels with ultra high performance concrete can be available through evaluation on shear, joint connection and anchoring, etc.

• Journal of Adhesion and Interface
• /
• v.16 no.4
• /
• pp.137-145
• /
• 2015

This study aimed to develop epoxy putty as a multi-purpose connection and restoration material that can be used for material-specific restoration work such as metal, wood, ceramics, earthenware and stone artifacts by replacing synthetic resins currently being used for preservation treatment of cultural assets. Existing synthetic resins have the issue of cutting force resulting from high strength, deflection resulting from long hardening time, contaminating the surface of artifacts through staining on tools or gloves and need for re-treatment resulting from material discoloration. Accordingly, paste type restoration material most widely being used in the field of cultural assets preservation treatment was selected and examined the property to select it as an object of comparison. Based on such process, epoxy putty was developed according to the kind of agent, hardener and filler. For the purpose of solving the issues of existing material and allowing the epoxy putty developed to have similar property, property experiments were conducted by selecting agents and hardeners with different characteristics and conditions. The study findings showed that both kinds are paste type that improved work convenience and deflection issue as a result of their work time of within 5~10 minutes that are about 3~10 times shorter than that of existing material. In regards to wear rate for increasing cutting force, it improved by about 3 times, thereby allowing easy molding. For the purpose of improving the issue of surface contamination that occurs during work process, talc and micro-ballon were added as filler to reduce the issue of stickiness and staining on hand. Furthermore, a multi-purpose restoration material with low shrinkage, low discoloration and high cutting force was developed with excellent coloring, lightweight and cutting force features.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.7
• /
• pp.936-944
• /
• 2019

Submarines, which have been called an invisible force, are strategic underwater weapon systems that perform missions such as anti-surface warfare, anti-submarine warfare, and high payoff target strikes with the advantage of underwater covertness. A submarine should be able to withstand the hydrostatic pressure of the deep sea. In this respect, the submarine pressure hull, as the main structural system to resist the external pressure corresponding to the submerged depth, should ensure the survivability from hazards and threats such as leakage, fires, shock, explosion, etc. To do this, the initial scantling of the submarine pressure hull must be calculated appropriately in the concept design phase. The shape of the aft transition ring varies according to its connection with the submarine aft end conical structure, pressure hull cylindrical part, and non-pressure hull of the submarine; the design of the aft transition ring should not only take into account stress flow and connectivity but also the cost increase due to the increased man-hours of its complex geometry. Therefore, trade-off studies based on the four different shapes of the aft transition ring are carried out considering both the review of the structural strength through nonlinear finite element analysis (FEA) and economic feasibility by reviewing the estimations of the manufacturing working days and material costs. Finally, the most rational structural aft transition ring shape for a submarine amongst four reviewed types was proposed.

• Strategy21
• /
• s.44
• /
• pp.5-27
• /
• 2018

The purpose of this paper is to look at USN's efforts to rebuild its combat power in the face of a reemergence of great powers competition, and to propose some recommendations for the ROKN. In addition to the plan to augment its fleet towards a 355-ships capacity, the USN is pursuing to improve exponentially combat lethality(quality) of its existing fleet by means of innovative science and technology. In other words, the USN is putting its utmost efforts to improve readiness of current forces, to modernize maintenance facilities such as naval shipyards, and simultaneously to invest in innovative weapons system R&D for the future. After all, the USN seems to pursue innovations in advanced military Science & Technology as the best way to ensure continued supremacy in the coming strategic competition between great powers. However, it is to be seen whether the USN can smoothly continue these efforts to rebuild combat strength vis-a-vis its new competition peers, namely China and Russian navy, due to the stringent fiscal constraints, originating, among others, from the 2011 Budget Control Act effective yet. Then, it seems to be China's unilateral and assertive behaviors to expand its maritime jurisdiction in the South China Sea that drives the USN's rebuild-up efforts of the future. Now, some changes began to be perceived in the basic framework of the hitherto regional maritime security, in the name of declining sea control of the USN as well as withering maritime order based on international law and norms. However, the ROK-US alliance system is the most excellent security mechanism upon which the ROK, as a trading power, depends for its survival and prosperity. In addition, as denuclearization of North Korea seems to take significant time and efforts to accomplish in the years to come, nuclear umbrella and extended deterrence by the US is still noting but indispensible for the security of the ROK. In this connection, the naval cooperation between ROKN and USN should be seen and strengthened as the most important deterrents to North Korean nuclear and missile threats, as well as to potential maritime provocation by neighboring countries. Based on these observations, this paper argues that the ROK Navy should try to expand its own deterrent capability by pursuing selective technological innovation in order to prevent this country's destiny from being dictated by other powers. In doing so, however, it may be too risky for the ROK to pursue the emerging, disruptive innovative technologies such as rail gun, hypersonic weapon... etc., due to enormous budget, time, and very thin chance of success. This paper recommends, therefore, to carefully select and extensively invest on the most cost-effective technological innovations, suitable in the operational environments of the ROK. In particular, this paper stresses the following six areas as most potential naval innovations for the ROK Navy: long range precision strike; air and missile defense at sea; ASW with various unmanned maritime system (UMS) such as USV, UUV based on advanced hydraulic acoustic sensor (Sonar) technology; network; digitalization for the use of AI and big data; and nuclear-powered attack submarines as a strategic deterrent.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.6
• /
• pp.1-8
• /
• 2018

FRP is a new material that is light, has high strength and high durability, and is emerging as a third construction material inside and outside of countries. However, very few studies have been done on curved FRP construction materials that can be used for tunnels or arched bridges. Because a small composite panel specimen is smaller than a full-size specimen, it can be used in a variety of experiments under different conditions. Therefore, in this study, experiments were performed on a void section, a solid section, a connected solid section, and a sand-coating solid section. The results of the experiment show that the connection of composite curved panels with longitudinal connections provides almost equivalent performance to that of a single panel. However, it is necessary to strengthen the connections, since the connections that are most susceptible to damage will break first.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.1
• /
• pp.55-68
• /
• 2014

In this study, the beam-to column connections of concrete-encased-and-filled steel tube columns were tested under cyclic loading. Two specimens using steel beams and two specimens using precast concrete beams were tested. The dimension of the column cross section was $670mm{\pm}670mm$. The beam depths were 488mm and 588mm for the steel beams and 700mm for the precast concrete beams. The longitudinal bar ratios of the precast concrete beams were 1.1% and 1.5%. For the connections to the steel beams, continuity plates were used in the tube columns. For the connections to the PC beams, couplers were used for beam re-bar connections. The test results showed that except for a specimen, deformation capacities of the specimens were greater than 4% rotation angle, which is the requirement for the Special Moment Frame. Particularly, specimens using precast concrete beam showed excellent performances in the strength, deformation, and energy dissipation.

• Korea and Global Affairs
• /
• v.3 no.2
• /
• pp.183-220
• /
• 2019

Nowadays, soft power is playing a more important role in international communication and cooperation, and as cultural exchange in regional cooperation is deeply influenced by national soft powers, the development is usually unbalanced. Bangladesh, China, India and Myanmar are adjacent to each other with a long history of intercourse. In the year 2013, initiation of constructing Bangladesh-China-India-Myanmar Economic Corridor advocated by China and India was responded positively by Bangladesh and Myanmar. Since then, the world has witnessed an increasing connection of these four countries. Being the critical bond connecting the southwestern areas of China and Bangladesh, India as well as Myanmar, Bangladesh-China-India-Myanmar Economic Corridor is characterized by multiple regional cultures along with frequent connections in cultural products and activities. However, cultural exchange now is dominated by imbalanced development due to potent soft power of China and India that these two countries export more cultural products to the rest, which has an impact in many fields of Bangladesh and Myanmar. Priority should be given to coordinated development in cultural exchange regarding the construction of Bangladesh-China-India-Myanmar Economic Corridor. Only by developing a sustainable development mechanism for cultural exchange, to coordinate the influences of soft powers of these four countries, then a fine complexion of "all flowers are in bloom" can be created, returning to five original intention of the construction of this economic corridor: "Policy Communication" and "Strength People-to-people Ties", etc.

• The Journal of the Convergence on Culture Technology
• /
• v.7 no.1
• /
• pp.291-299
• /
• 2021

In 2019, SUV sales surpassed sedans in the domestic sales market with phenomenal domestic sales. The strength of SUVs around the world is expected to continue in the future. South Korea's K-company aggressively launched small SUVs in the SUV market. Its simple lineup is recognized as a brand image, not as a SUV. It is time to evaluate this. Therefore, it influences the purchasing decisions of potential customers and buyers of small SUVs through the evaluation of design images of small SUVs in Korea. Rather than the functional properties of the SUV model, it is purchased by emotional characteristics, brand symbolism, and image. Subconsciousness of the purchasing psychology of the end consumer was used by metaphor extraction techniques. Customers wanted to study the evaluation of small SUV design images that fit their needs. We wanted to see if consumers who intend to purchase or purchase small SUVs in Korea had a connection with the image of design of small SUVs in Korea. The conclusion of the study was extracted through ZMET, a metaphor extraction technique, with the latent consciousness of the primary ambiguous message from the consumer's feeling and representation of the image. Therefore, based on the results of this study, we hope that the images presented in SUVs in the future will be used as a design guide in the development of small SUVs to influence customer thinking and behavior.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.19 no.5
• /
• pp.59-69
• /
• 2009

RFID tag search system which is used to find a specific tag has an application such as asset management, supply chain, and this search scheme has been given much attention so far. In RFID tag search system, especially, mobility of the reader is important in order to search tags. Therefore, even though the handheld reader cannot connect with the central database because of unreliable wireless connection or remote location, handheld reader should search the specific tag without help of the central database. In addition, in RFID tag search system, users hold not the tag but the reader, the privacy of users should be considered. Since the signal strength of the reader is stronger than that of the tag, the privacy of the reader holder is very important. Recently, in order to solve these problems, a number of RFID tag search schemes have been proposed. However, since these schemes did not consider the privacy of reader holders, there are serious privacy breaches of reader holders. In this paper, we propose efficient RFID tag search protocol for passive tags. Our proposed scheme preserves the privacy of reader holders.