• Journal of the Korean Society for Heat Treatment
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• v.30 no.1
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• pp.17-20
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• 2017

Mechanical properties of STD61 steel are compared with those of carburized STD61 steel when both are quenched and tempered in vacuum heat treatment. Mechanical properties of carburized STD61 steel are improved better than STD61 steel in hardness, tensile strength, impact energy and wear resistance.

• Journal of Welding and Joining
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• v.5 no.2
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• pp.27-34
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• 1987

The characteristics of arc sprayed layer were studied with hardness test and microstructural observation. The erosion resistance of arc sprayed layer was also evaluated using a method of steel ball blasting test which was proposed in this study as a test method for measuring the erosion properties in the impact wear condition. By an impact of the molten droplets on the redeposited substrate, lamella structure was formed which contains laminated oxide layers, fissures, and porosities. As a result of mechanical tests, it was shown that the sprayed specimen showed higher hardness than the substrate, but it resulted in higher erosion rate than the substrate. The poor erosion property obtained with a sprayed coating was considered to be attributable to easy flaking off the the layers laminated with brittle oxide layers.

• Journal of Korea Foundry Society
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• v.29 no.6
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• pp.251-256
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• 2009

The effect of austempering treatment on mechanical properties of nodular indefinite chilled iron(NICI) and ductile cast iron(DCI) was investigated. In microstructural observation, matrix phase(pearlite and ferrite) was changed to ausferrite after austempering treatment both DCI and NICI. In case of NICI, decomposition of cementite($Fe_3C$) during austempering treatment was induced. After austempering treatment, mechanical properties such as hardness, tensile strength and impact toughness was improved in NICI and DCI. The wear resistance is slightly decreased because of decomposition of cementite during austempering treatment in NICI but impact toughness and strength is dramatically increased.

• KDI Journal of Economic Policy
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• v.43 no.2
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• pp.103-123
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• 2021

This paper examines the impact of the regional cash subsidies which were granted in some districts in addition to the national universal stimulus payment in South Korea related to the COVID-19 pandemic. We evaluate the effects of the cash distribution per resident on aggregate credit and debit card sales and sales by industry using the difference-in-difference method. The increment in card spending due to the cash subsidy is about 1.58%p in total, and this effect is concentrated within a single month. The consumption stimulating effect is prominent among (semi)-durable goods that do not require close interactions between customers and sellers. In contrast, the effect is relatively small in the high-contact face-to-face service sectors and restaurants, areas the COVID-19 pandemic hit directly. On the other hand, some service sectors where customers could wear face masks, such as education and fitness, experienced a substantial sales boost due to the cash subsidy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.899-904
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• 2001

The impact of PVD coatings can be summed up in practical terms: this technology historically complements the best designed tool substrates to enhance cutting performance. PVD coatings are now incorporated in 25% of all HSS tools. The functionality is to extend the machining speed range, improve wear resistance at the cutting edge, and reduce friction at chip/tool contact areas to allow easier chip evacuation. These translate to a larger safe zone, as discussed in the failure mode diagram, for better productivity and higher reliability in machining operations of the customer. PVD coatings therefore represent an enabling technology that extends the application range of cutting tools in response to modern industrial needs. PVD coatings prolong the product life cycle of HSS tools and help this "mature" material to hold its territory against the advent of the newer hardmetal and ceramic tool materials. There is a lot of competitive life left particularly in PVD coated HSS endmills, drills, threading/tapping tools. PM HSS technology further increases the possibilities.ibilities.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.37-52
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• 2017

Gas turbines operating in dusty or sandy environment polluted with micron-sized solid particles are highly prone to blade surface erosion damage in compressor stages and molten sand attack in the hot-sections of turbine stages. Commercial/Military fixed-wing aircraft engines and helicopter engines often have to operate over sandy terrains in the middle eastern countries or in volcanic zones; on the other hand gas turbines in marine applications are subjected to salt spray, while the coal-burning industrial power generation turbines are subjected to fly-ash. The presence of solid particles in the working fluid medium has an adverse effect on the durability of these engines as well as performance. Typical turbine blade damages include blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicate (CMAS) attack, oxidation, plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. The focus of this research work is to simulate particle-surface kinetic interaction on typical turbomachinery material targets using non-linear dynamic impact analysis. The objective of this research is to understand the interfacial kinetic behaviors that can provide insights into the physics of particle interactions and to enable leap ahead technologies in material choices and to develop sand-phobic thermal barrier coatings for turbine blades. This paper outlines the research efforts at the U.S Army Research Laboratory to come up with novel turbine blade multifunctional protective coatings that are sand-phobic, sand impact wear resistant, as well as have very low thermal conductivity for improved performance of future gas turbine engines. The research scope includes development of protective coatings for both nickel-based super alloys and ceramic matrix composites.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.491-497
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• 2005

Brake system is indispensible functional part to the transportation machines such as railroad cars, and all of industrial machines. It is mechanical element to stop the movement or slow the speed, transforming kinetic energy of motion object into thermal energy through solid friction. According that recently the railroad cars have become high-speed, the technique in braking domain to secure the overall braking effort is making rapid progress. In particular, material development and manufacturing process are so important to secure friction performance, which is the core in braking performance of mechanical brake units. Wear of brake disk could mainly result in the diminishment of its life span due to thermal cracking, so the endurance against high temperature is required. On the other hand, in this case, the problem is that the side wear of pad, relative material is slightly increased because of enlargement of plastic deformation. It is necessary, therefore, to develop a disk material that will be used in the Tilting System mechanical brake units. The purpose of this paper is to make a study prior to developing brake disk of Tilting Train travelling at 200km/h and to propose the component of brake disk. Accordingly, I will conduct sufficient researches on technical documents of brake disk, that are basic documentations, analyze an impact on components, and further, considering braking degree of train, study for the basic proposal on brake disk's component of the train travelling at 200km/h, which has relatively minor influence of heat stress and maintains the friction. In this respect, I would like to investigate friction characteristics between disk and relative friction material via Test on some possible test segments, analyze and propose friction performance, temperature impact and so forth coming from the contact with pad, relative material to demonstrate the friction characteristics.

• Journal of the Korea Society of Computer and Information
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• v.27 no.9
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• pp.157-167
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• 2022

This study attempted to investigate what kind of perception people in their 20s have about masks and to find out the characteristics of each type by categorizing the perception. The Q methodology was used for the study. The cognition types of masks were categorized into three. Type 1 was a 'always wear impact-important type' that always wears masks and thinks masks affect non-verbal communication and the wearer's image. Type 2 was a 'function-important negative recognition type' that wears masks to prevent germs and thinks that masks have a great negative impact. Type 3 was a 'concealment wear positive image type' that wears a mask to cover the face and thinks that a person looks young when wearing a mask. It is thought that the development of masks of various designs and functions reflecting the needs of consumers should be carried out. Also, it is thought that various products should be developed and sold so that consumers can choose according to important considerations such as design, fit, and function.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1004-1007
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• 2001

This paper presents the experimental results to verify the environmental consciousness with economic balances due to cutting fluid behaviors, effectiveness in machining process. Even though cutting fluid improves the machined part quality through the cooling and lubracating effects, its environmental impact is also increased according to the cutting fluid usage. Because cutting fluid are used by experience than science on shop floors, its environmental impact are more serious to human health hazard, shop floor environments. In this study a few cutting parameters are adopted as the machinability index (i.e. ; tool wear and surface roughness), and aerosol mist diffusion rate of cutting fluid as the environment consciousness index. These indeces are analyzed quantitatively via a few experiements. The results of this study can be facilitate the optimization of cutting fluid usage in achieving a balanced environmental consciousness consideration with economic view.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.239-242
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• 2004

We investigated the nanotopography impact on the post-chemical mechanical polishing (post-CMP) oxide thickness deviation(OTD) of ceria slurry with a surfactant. Not only the surfactant but also the slurry abrasive size influenced the nanotopography impact. The magnitude of the post-CMP OTD increased with adding the surfactant in the case of smaller abrasives, but it did not increase in the case of larger abrasives, while the magnitudes of the nanotopography heights are all similar. We created a one-dimensional numercal simulation of the nanotopography impact by taking account of the non-Prestonian behavior of the slurry, and good agreement with experiment results was obtained.