• Journal of the Korea Safety Management & Science
• /
• v.26 no.2
• /
• pp.11-22
• /
• 2024

This study aims to present safety distances by the damage impact assessment of the leakage of propylene oxide. As a result of the experiment, the pressure 1psi range was 52m to 169m, the radiant heat 18kW/m² range was 63m to 163m, the AEGL-2 range was analyzed as 224m to 414m, and the fire ball diameter was analyzed to be 45m to 121m. Additionally, the extent of damages was proportional to the amount of propylene oxide stored or handled. The safe distance for a 10% lethality due to overpressure and radiant heat was calculated to be 134m, and the safe distance for a 0% lethality was 169m. Toxicity was measured at 134m with a lethality 0%. Therefore, the safety distance due to leakage of propylene oxide is calculated to be between 134m and 169m.

• Transactions of Materials Processing
• /
• v.33 no.2
• /
• pp.118-122
• /
• 2024

Micro-electromechanical systems (MEMS) based in-situ heating holders have been developed to enable high resolution imaging of heat treatment analysis. However, unlike the standard 3 mm metal disk specimens used in the furnace-based heating holder and general transmission electron microscopy holder, the MEMS-based in-situ heating holder requires thin specimens that can be penetrated by electrons to be transferred onto the MEMS chip. Previously, focused ion beam milling was used to transfer metal specimens, but it has the disadvantage of being expensive and the risk of specimen damage due to gallium ions. Therefore, in this study, we devised a method of transferring metallic materials by ultrasonic treatment using a transmission electron microscopy specimen made by electro jet polishing. A 3mm electropolished metal disk was placed in an appropriate solution, ultrasonicated, and then drop casted. The transfer of the specimen was successful, but it was confirmed that dislocations were formed inside the specimen due to ultrasonic treatment. This study provides a novel method for transferring metallic materials onto MEMS chips, which is cost-effective and less gallium ion damaging to the specimen. The results of this study can be used to improve the efficiency of heat treatment analysis using MEMS-based in-situ heating holders.

• Journal of Life Science
• /
• v.19 no.4
• /
• pp.429-435
• /
• 2009

Oxidative stress is a consequence of an imbalance of the defense system against cellular damage generated by reactive oxygen species (ROSs) such as superoxide anions (menadione; MD). Most organisms have evolved a variety of defense systems to protect cells from adverse conditions. In order to evaluate stress tolerance against oxidative stress generating MD, comparative analyses of antioxidant capacity, or free radical scavenger ability, were performed between S. cerevisiae KNU5377 (KNU5377) and three wild-type S. cerevisiae strains. In a medium containing 0.4 mM MD, the KNU5377 strain showed higher cell viability and antioxidant ability, and contained higher levels of trehalose, superoxide dismutase, thioredoxin system, glucose-6-phosphate dehydrogenase, and some heat shock proteins. The KNU5377 strain also produced a lower level of oxidative stress biomarker than the other three yeast strains. These results indicate that S. cerevisiae KNU5377 has a higher level of tolerance to oxidative stress due to the increased expression of cell rescue proteins and molecules, thus alleviating cellular damage more efficiently than other S. cerevisiae strains.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.4
• /
• pp.1178-1185
• /
• 2010

Recently, high speed of container freight cars is causing fatigue damage of wheel. Sudden failure accidents cause a lot of physical and human damages. Therefore, damage analysis for wheel prevents failure accident of container freight car. Wheel receives mechanical and thermal loads at the same time while rolling stocks are run. The mechanical loads applied to wheel are classified by the horizontal load from contact of wheel and rail in curve line section and by the vertical force from rolling stocks weight. Also, braking and deceleration of rolling stocks cause repeated thermal load by wheel tread braking. Specially, braking of rolling stocks is frictional braking method that brake shoe is contacted in wheel tread by high breaking pressure. Frictional heat energy occurs on the contact surface between wheel tread and brake shoe. This braking converts kinetic energy of rolling stocks into heat energy by friction. This raises temperature rapidly and generates thermal loads in wheel and brake shoe. There mechanical and thermal loads generate crack and residual stress in wheel. Wetenkamp estimated temperature distribution of brake shoe experimentally. Donzella proposed fatigue life using thermal stress and residual stress. However, the load applied to wheel in aforementioned most researches considered thermal load and mechanical vertical load. Exact horizontal load is not considered as the load applied to wheel. Therefore, above-mentioned loading methods could not be applied to estimate actual stress applied to wheel. Therefore, this study proposed safety estimation on wheel of freight car using heat-structural coupled analysis on the basis of loading condition and stress intensity factor.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.589-592
• /
• 2008

This study was conducted to assess the durability of Chloride-inhibiting Low-Heat Cement while being subjected to freezing-thawing during winter seasons. Although durability varies slightly depending on the conditions of the jobsite, frost damage to concrete resulting from repeated freezing and thawing over the course of seasonal changes is the leading cause behind lowered concrete durability. in addition, concrete that has been subjected to freezing and thawing during the winter season develops a significant amount of expansive force at the core and begins to exhibit signs of damage, such as cracking, peeling, and detachment from the aggregate. Therefore, this study fabricated test specimens using a Chloride-inhibiting Low-Heat Cement(CLC) and the widely used blast furnace slag cement(BFS) and Ordinary Portland Cement(OPC) with water-to-cement ratios of 35%, 40% and 45%, respectively, to assess the durability index of the CLC as per resistance to freezing-thawing. The specimens were then tested using the KS F 2456 method (Testing method for resistance of concrete to rapid freezing and thawing) to measure the dynamic modulus of elasticity. The dynamic modulus of elasticity measurements were then used to derive the durability indices. By comparing the durability indices, it was confirmed that CLC, BFS, and OPC all had superior durability.

• Journal of Surface Science and Engineering
• /
• v.42 no.6
• /
• pp.287-293
• /
• 2009

The passivation films with epoxy layer on LiF, $SiN_x$ and LiF/$SiN_x$ inorganic layer were fabricated on OLED to protect device from the direct damage of $O_2$ and $H_2O$ and to apply for a buffer layer between OLED device and passivation multi-layer with organic/inorganic hybrid structure as to diminish the thermal stress and expansion. Red OLED doped with 1 vol.% Rubrene in $Alq_3$ was used as a basic device. The device structure was multi-layer of ITO(150 nm) / ELM200_HIL(50 nm) / ELM002_HTL(30 nm) / $Alq_3$: 1 vol.% Rubrene(30 nm) / $Alq_3$(30 nm) / LiF(0.7 nm) / Al(100 nm). LiF/epoxy applied as a protective layer didn't contribute to the improvement of life time. While in case of $SiN_x$/epoxy, damage was done in the passivation process because of difference in heat expansion between films which could occur during the formation of epoxy film. Using LiF/$SiN_x$/epoxy improved lifetime significantly without suffering damage in the process of forming films, therefore, the best structure of passivation film with inorganic/epoxy layers was LiF/$SiN_x$/E1.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.7
• /
• pp.1042-1049
• /
• 1997

LMFBR(Liquid Metal Fast Breeder Reactor) vessel is operated under the high temperatures of 500-550.deg. C. Thus, transient thermal loads were severe enough to cause inelastic deformation due to creep-fatigue and plasticity. For reduction of such inelastic deformations, Y-piece structure in the form of a thermal sleeve is used in LMFBR vessel under repeated start-up, service and shut-down conditions. Therefore, a systematic method for inelastic analysis is needed for design of the Y-piece structure subjected to such loading conditions. In the present investigation, finite element analysis of heat transfer and inelastic thermal stress were carried out for the Y-piece structure in LMFBR vessel under service conditions. For such analysis, ABAQUS program was employed based on the elasto-plastic and Chaboche viscoplastic constitutive equations. Based on numerical data obtained from the analysis, creep-fatigue damage estimation according to ASME Code Case N-47 was made and compared to each other. Finally, it was found out that the numerical predictio of damage level due to creep based on Chaboche unified viscoplastic constitutive equation was relatively better compared to elasto-plastic constitutive formulation.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.297.2-297.2
• /
• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• Journal of the Korean GEO-environmental Society
• /
• v.18 no.3
• /
• pp.15-23
• /
• 2017

Gangwon Province, located in the northeastern part of South Korea, is the coldest area in South Korea with 90% of the total area as mountainous. Therefore, tunnel damage has been reported continuously in winter. But there has been lack of researches on frost heave occurring behind tunnel lining. In this study, numerical analysis was conducted to investigate the frost depth in road tunnel constructed in Gangwon province. Based on the database on road tunnel and weather in Gangwon province, a standard tunnel shape and geotechnical properties of ground was determined. And then thermal analysis for the frost depth according to the temperature change and ground conditions were conducted. Analysis result showed that the sensitivity to frost heave of metamorphic rock and sedimentary rock is higher than sand. Lower initial ground temperature leads to deeper frost depth and consequently increases frost damage. In addition, lining thickness, specific heat capacity, and thermal conductivity also affect greatly on the variation of frost depth.

• Journal of Power System Engineering
• /
• v.16 no.1
• /
• pp.58-64
• /
• 2012

Power plant boiler is one of the most important utilities providing steam to turbine in thermal power plant. It is composed of thousands of boiler tubes for high efficient heat transfer. Boiler tube material is used in such high temperature and pressure as $540^{\circ}C$, $170kg/mm^2$. The boiler tube material is needed to resist corrosion damage, creep damage and fatigue damage. 2.25%Cr-1Mo steel is used for conventional boiler tubes. In these days steam temperature and pressure of the power plant became higher for high plant efficiency. So, the material property of boiler tube must be upgraded to meet the plant property. Several boiler tube material was developed to meet such condition. X20CrMoV12.1 steel is also developed in early 1980's and used for superheater and reheater tubes in supercritical boilers. The material has martensitic structure, which is difficult to evaluate the material degradation. Boiler tube material at severe condition was tested to evaluate long term and short term degradation and creep. Through long term and high temperature degradation test, lath structure was decreased and recrystallization has been proceeded by sub-crystal. And in this research the effect of temperature and stress on boiler tube characteristic,for example, deformation by creep was changed rapidly at relatively high temperature and stress because creep was affected easily by temperature and stress.