• 대한기계학회논문집
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• 제7권4호
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• pp.355-360
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• 1983

This paper deals with fatigue behavior of ion-nitrided coil spring. It is found that fatigue limit can be significantly increased by ion-nitriding. Ion-nitribed specimen which is treated at 550.deg. C for 5 hours improves in the fatigue limit by 30 percent in comparison with that of non-nitrided specimen. On the other hand, the value of spring constant K has nothing to do with nitriding time and temperature in this experimental range. Besides fatigue behavior, the following effects are discussed such as compound layer, diffusion layer, hardness distribution and their relations.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 2003년도 추계 학술논문발표회 논문집
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• pp.154-159
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• 2003

화학공장과 제조업 등의 사업장에서 발생하는 화재 및 폭발은 설비와 건물의 파괴뿐만 아니라 사업장의 근로자와 인근 주민에 대한 인명 피해까지 초래하는 경우가 많으므로 공정 안전을 위해 화재 및 폭발 분야의 연구에 많은 관심을 가져야 한다. 방화(Fire Protection) 및 방폭(Fire Protection)에 관련되는 특성치로 MSDS의 5번째 항목인 폭발화재시대처방법(Fire-fighting Measures)에서는 폭발(연소)한계(Explosive Limit 혹은 Flammability Limit), 인화점(Flash Point), 최소발화온도(AIT： Auto-ignition Temperature)가 제시되고 있다.(중략)

• 대한기계학회논문집A
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• 제33권10호
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• pp.1158-1162
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• 2009

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26${\mu}m$ thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

• 한국화재소방학회논문지
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• 제29권6호
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• pp.20-25
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• 2015

2-Ethylhexanoic acid는 플라스틱의 충격보강제를 제조하는 물질로서 공정 중에 폭발위험성을 고찰하기 위하여 산소농도 변화에 따른 폭발범위, 폭발압력, 최대폭발압력상승속도를 실험한 결과 실험온도 $100^{\circ}C$에서, 산소농도 40~70%에서 폭발하한농도 3.2%를 구하였으며, 산소농도 21%에서 폭발하한 농도는 4.0%, 폭발상한 농도는 4.5%를 구하였다. 또한, 2-ethylhexanoic acid의 폭발압력은 산소농도 70%에서 1.4161 MPa의 최대폭발압력을 나타내었으며, 최대폭발압력상승속도를 구한 결과 산소농도 70%에서 62.692MPa/s를 구하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.117-120
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• 2003

Warm deep drawing which is one of the new forming technologies to improve formability of sheet metal is applied to the cylindrical cup drawing of Mg-alloy sheet metal. In experiments the temperature of die and blank holder is varied from room temperature to $300^{\circ}C$, while the punch is cooled by circulation of coolant to increase the fracture strength of workpiece on the punch corner area. Test material chosen for experiments is AZ31 magnesium sheet metal. Teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ratio as well as thickness distributions of drawn cups are investigated and validity of warm deep drawing process is also discussed.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1089-1096
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• 2003

An experiment was performed to investigate lift-off, blow-off and combustion characteristics of a lifted coaxial diffusion flame according to fuel jet and air velocity. A jet diffusion flame which is attached on the nozzle rim begins to be lifted with increase of air velocity, and finally becomes blow-off at higher air velocity. In experiment, blow-off limit increased with increase of fuel jet velocity, however lift-off occurred at lower air velocity. Flame structure and combustion characteristics were examined by schlieren photos, temperature distributions and emission concentration distributions. Flame temperature became higher at midstream and its RMS became larger at up and downstream with increase of air velocity. Local NO concentration decreased but $CO_2$concentration increased with increase of air velocity, which shows combustion reaction becomes close to be stoichiometric at higher air velocity in spite of lift-off.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1134-1139
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• 2004

Recently, development of flame control scheme has been hot issues in the combustion engineering. It has been held that flame shape can be controllable by pressure inside combustor. The influence of combustor atmospheric pressure on flame shape was investigated in the present study. The flame shape, flammable limit, flame temperature and nitric oxide emission were measured as functions of combustor atmospheric pressure and equivalence ratio. The reaction region became longer and wider with decreasing combustor atmospheric pressure by direct photography, hence reduction of blow off limit. This tendency was also observed in the mean flame temperature distribution. Nitric oxide emission decreased with decreasing combustor atmospheric pressure. Low NOx combustion is ascribed to wide-spread reaction region in the low atmospheric pressure condition. These results demonstrate that flame shape and nitric oxide emission can be controllable with combustor atmospheric pressure.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.630-633
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• 2004

Generally, component and FR-4 board are connected by solder joint. Because material properties of components and FR-4 board are different, component and FR-4 board show different coefficients of thermal expansion (CTE) and thus strains in component and board are different when they are heated. That is, the differences in CTE of component and FR-4 board cause the dissimilarity in shear strain and BGA solder joint s failure. The first order Taylor series expansion of the limit state function incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. A model based on plastic-strain rate such as the Coffin-Manson Fatigue Model is utilized in this study. The effects of random variables such as frequency, maximum temperature, and temperature variations on the failure probability of the BGA solder joint are systematically investigated by using a failure probability model with the first order reliability method(FORM).

• 한국정밀공학회지
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• 제27권9호
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• pp.78-85
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• 2010

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polycarbonate(PC) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PC at room temperature is 85 % of tensile strength. which is higher than PE (75%)at room temperature. Also the creep limits decreased exponentially as the temperatures increased, up to 50 % of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages was non-existent nor was there any rupture failure which occurred for many metals.

• Progress in Superconductivity
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• 제3권2호
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• pp.146-150
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• 2002

We performed the point contact spectroscopy on newly discovered superconductor $MgB_2$ thin films with Au tip. In the point contact spectroscopy of the metallic Sharvin limit, the differential conductance below the gap is twice as that above the gap by virtue of Andreev Reflection. After some surface cleaning processes of sample preparation such as ion-milling and wet etching, the obtained dI/dV versus voltage curves are relatively well fitted to the Blonder-Tinkham-Klapwijk (BTK) formalism. Gaps determined by this technique were distributed in the range of 3meV~ 8meV with the BCS value of 5.9meV in the weak coupling limit. We attribute these discrepancies to the symmetry of the gap parameter and the degradation of the surface of the sample. We also present the temperature dependence of the conductance vs voltage curve and thereby the temperature dependence of the gap.