• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.134-142
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• 1998

The effects of small hole defect size and effective case depth(ECD) on the four point bending fatigue limit of induction surface hardened S45C steel were investigated the fatigue limit evaluation of hardened materials is very difficult because of relations of the hardness gradient and residual stress. In this study, it was possible to characterize fatigue limit and fatigue life of induction surface hardened S45C steel in terms of the hole defect size and effective case depth(ECD) and quantitative evaluation of the fatigue limit with hole defects use Murakami's evaluation method and the range of evaluated values is a good accuracy compared with results.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.341-347
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• 2005

본 논문은 터널에서 화재 발생 시, 시간에 따른 연기거동에 대해 실물실험과 3차원 수치해석을 수행하고 각각의 결과를 비교,검토하였다. 실물실험을 위하여 8.8 kW의 열원과 901iter/h의 연기 발생이 가능한 연기발생장치를 자체 제작하였으며, 대상터널은 길이 570m, 단면적 $64.6m^2,$ 그리고 약 $2\%$의 구배를 가지고 있다. 실험은 외풍의 영향을 줄이기 위해 터널 입,출구에 차단막을 설치하였으며 연기발생장치로부터 20m 간격의 위치에서 20초 간격으로 연기전파, 속도 그리고 온도를 측정하였다. 연기는 60초 경과 후, 연기발생장치로부터 20m 떨어진 위치에 도달하였으며 140초, 180초 및 260초 경과 후, 각각 40m, 60m 및 80m 위치에 도달하였다. 3차원 수치해석의 결과는 터널벽면을 매끈한 표면으로 처리하였을 때, $26.3\~49.5\%$정도 과대 예측하였다. 또한 터널벽면을 일정 조도를 갖는 거친 표면으로 처리한 경우는 $-2.7\~17.6\%$ 오차로 실험결과에 보다 근접하는 결과를 보였다. 따라서 터널 내 연기거동에 대한 3차원 수치해석을 수행할 때에는 벽면조도에 대한 고려가 필요하리라 판단된다.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.333-338
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• 2000

Induction surface hardening is widely used to enhance local strength and hardness. However, most research is only to have a focus on fatigue life and fatigue behavior is not so much studied. So, in this study, Cr-Mo steel alloy(SCM440) was used to show the effect of residual stress and micro hole on the fatigue strength for base metal and induction surface hardened specimen. In addition, the fatigue characteristic between surface hardened and fully hardened steel is somewhat different. It is caused by hardness distribution, residual stress and inclusions etc.. Crack origins are generally micro inclusions for the high strength steel. So, the distribution of inclusions is analyzed statistically.

• Fire Science and Engineering
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• v.12 no.4
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• pp.13-19
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• 1998

We investigated the weight loss according to temperature using Thermal Gravimetric Analysis(TGA) in order to find the thermal hazard of carbon black(Hi-Black 10, Hi-Black 50L) dusts, and the properties of dust explosion in variation of the surface functional groups and specific surface area of their dust with the same particle size. Using Hartman's dust explosion apparatus which estimate dust explosion by electric ignition after making dust disperse by compressed air, dust explosion experiments have been conducted by varying concentration and size of carbon black dust. The explosion pressure of both carbon black increased as the specific surface area increased. The results indicated that Hi-Block 50L of which specific surface area was larger three to four times than that of Hi-Black 10 was much easier of dust explosion.

• Fire Science and Engineering
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• v.23 no.5
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• pp.72-77
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• 2009

In the recycling procedure of the refrigerator, the fire frequently breaks out. In this study, to clarify the exact cause of the fire, the components and concentration of the materials produced in the process are analysed as well as the problems in the process system, and the protective measure to prevent the fire and the explosion fundamentally is proposed. In this procedure, the preventive measures of fire by removing the combustible materials such as polyurethane and inflammable gases, by removing the ignition sources and by reducing the oxygen concentration to the minimum are proposed along with the protective measures to reduce the damage in the fire. In the crushing procedure where the fire or explosion can break out in diverse ways, the forced ventilation or exhaust system applied to the small partial ventilation facility are installed to reduce the concentration of inflammable gas mixture to lower than the inflammable limit by injecting and exhausting the air forcibly.

• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.20-27
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• 1999

The standard of the allowed stress in designing components such as shafts used in machinery and aircraft should be determined. It is very important to estimate fatigue strength of a component analytically, because service stress of the components is usually under the level of its fatigue limit. Improving the fatigue strength of each component in machinery is essential for high performance, lightness, and endurance. Surface treatment of components is widely used for these purpose. In this research, the fatigue behaviors of SCM415 steel and carbonitried SCM415 steel are examined. In the analysis of the fatigue behaviors of the carbonitrided SCM 415 steel, we propose a modified fatigue strength evaluation model and modified formulae.

• Journal of the Korean GEO-environmental Society
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• v.14 no.6
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• pp.31-38
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• 2013

This study carried out fundamental study on the forest road pavement method of cementing the ground using the compaction equipment after laying by mixing with eco-friendly stabilizer, natural soil and water. Target strength of pavement was set to 2.0MPa and the specimen was produced per mixing ratio of cement, kinds of natural soil and curing period to evaluate the durability and unconfined compressive strength. Unconfined compressive strength test was conducted to compare strength by producing the test specimen mixing environment-friendly cement as well as the test specimen mixing cement with the same mixing ratio. To evaluate the durability, surface abrasion test and water flow resistance test were conducted. In addition, SB and GB tests were conducted using iron marble and golf ball to evaluate the walking satisfaction since it can be used by visitors due to the feature of forest road.

• Fire Science and Engineering
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• v.33 no.2
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• pp.30-38
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• 2019

Tracking, which is one of the main causes of electrical fires, is perceived as a physical phenomenon of electrical discharge. Hence tracking should be explained based on electric field analysis, conduction path by electron generation, and gas discharge physics. However, few papers have considered these details. This paper proposes a tracking mechanism including their effects on tracking progress. In order to prove this mechanism, a tracking experiment, an electric field analysis for the carbonization evolution model, and an explanation of the tracking process by gas discharge physics were conducted. From the tracking experiment, the current waveforms were measured at each stage of the tracking progress from corona discharge to tracking breakdown. The electric field analysis was carried out in order to determine the electric field on the surface of a dry-band and the high electric field region for electron generation during the generation and progress of carbonization. In this paper, the proposed tracking mechanism consisted of six stages including electron avalanche by corona discharge, accumulation of positive ions, expansion of electron avalanche, secondary electron emission avalanche, streamer, and tracking by conductive path. The pulse current waveforms measured in the tracking experiment can be explained by the proposed tracking mechanism. The results of this study will be used as the technical data to detect tracking phenomenon, which is the cause of electric fire, and to improve the proof tracking index.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.829-832
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• 2008

Since the early 1980s, the building is dramatically higher increases. Therefore, the shortage of parking spaces as a social problem has been pointed out. The parking lot utilization of underground space is increasing by like this problem solving countermeasure. However, Most of the organic material is used for construction in the parking lot on the floor. The existing parking zone flooring occupancy surface finishing is harmful gases and environmental hormones cause of the worker. The study on the safety of the worker consider using environment-friendly?high-liquidity ceramic resin mortar materials to evaluate the characteristics and physical properties.

• Journal of the Korea Institute of Building Construction
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• v.13 no.2
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• pp.122-130
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• 2013

One of recent methods to protect wooden cultural assets from fire, there is the flame retardation which is applied directly to wood and it is to prevent fire through securing flame resistance for the material and delaying combustion when failed fire in advance and then to gain time for people in the room to evacuate and it has same goal with the Korean Fire Service Act by protecting life and property. However, in case of spraying flame retardant on the colored surface of the wooden cultural assets, there are continuous problems of decoloration, efflorescence and water absorbtion after sometime and accordingly there increases danger of damages of cultural assets. So when treating with flame retardant on wooden cultural assets, there has to be no problems on dancheong after sometime and securing sustainable methods for flmae retardation should be preceded. Accordingly, this study aims to provide basic sources for selecting proper flame retardation methods by evaluating and analyzing flame retardation capabilities according to types of flame retardants which are frequently used nowadays and spraying them on the dancheong-painted surface and confirming if there is no problem on the dancheong and wood after sometime and if flame retardation effect is sustainable with its quality and capability through precise analysis.