• 대한기계학회논문집A
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• 제20권11호
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• pp.3415-3423
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• 1996

The compact tension specimen geometry has been widely used for measuring fatigue crack growth rates at elevated temperature when the fatigue load is under tension/tension condition. However, most of the elevated temperature components which have significant crack growth life experience fatigue load under tension/compression conditions. Thus test techniques are required since the compact tension specimen cannot be used for tension/compression loading. In this paper, a simplified test procedure for measureing fatigue crack growth rates is proposed, which employs a round bar specimen with a small surface crack. Fatigue crack growth rates under tension/ tension loading conditions at elevated temperature were measured according to the proposed procedure and compared with those previously measured by C/(T) specimens. Since both the measured crack growth rates were comparable, the fatigue crack growth rates under tension/ compression load can be reliably measured by the proposed procedure. For monitoring crack depth. DC electric potential method is employed and an optimal probe location and current input conditions were proposed.

• 대한기계학회논문집A
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• 제33권8호
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• pp.793-798
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• 2009

In this paper, the simulation and optimization of SRH (Surface Relief Hologram) masks for printing LCD gate patterns using TIR (Total Internal Reflection) holographic lithography was investigated. A simulation and optimization algorithm based on SDTA (Scalar Diffraction Theory Analysis) method was developed. The accuracy of the algorithm was compared to that of the RCWA (Rigorous Coupled Wave Analysis) method for estimating the Fresnel diffraction pattern of Cr amplitude masks for the given system geometry. In addition, the results from the optimization algorithm were validated experimentally. It was found that one to the most important conditions for the fabrication of SRH masks is to avoid nonlinear shape distortions of the resulting grating. These distortions can be avoided by designing SRH masks with recorded gratings having small aspect ratios of width versus depth. The optimum gap size between the Cr and SRH masks was found using the optimization algorithm. A printed LCD gate pattern with a minimum line width of $1.5{\mu}m$ exposed using the optimized SRH mask was experimentally demonstrated.

• 대한전자공학회논문지SP
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• 제46권1호
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• pp.56-62
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• 2009

산업용 강판튜브 CR영상의 잡음특성과 기하학적 구조에 관한 해석적 접근을 시도한다. 산업현장에서 방사선 측정실험으로 직접 취득한 방사선영상을 방사선강도에 따라 30(개) 이상의 샘플을 수집하였다. 이들 각 영상은 배경부, 두께부 및 튜브내부의 세 영역으로 구성되었는바, 그 가운데 튜브내부영역을 분석 대상으로 삼았다. 통계적이고 함수적인 방법론에 의해 잡음특성을 포함한 기하학적 구조를 분석한다. 영상을 구성하는 화소라인별로 또는 공간적으로 분석을 수행하여 강판튜브의 기하학적 원형 형태가 방사선영상화 과정을 거치면서 일어나는 변형과 잡음속성 변화의 두 가지 특성을 규명한다. 분석시 부합함수와 그 오차를 기하학적 변형의 판별인자로, 표준편차, 평균 및 SN비를 잡음특성 판별인자로 설정하고 방사선투과정도의 영상에서의 실현인 회색도 변화에 따른 이들 인자들의 변화를 고찰하였다. 분석결과, 본래의 원형 구조가 방사선투과 강도에 따라 타원형에서 저반경 원형 그리고 고반경원형의 점차적인 구조 변형을 일으킨다는 사실을 밝혔고, 잡음의 편차가 투과강도에 반비례함을 규명하였다.

• Journal of Radiation Protection and Research
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• 제14권2호
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• pp.10-17
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• 1989

옥외 라돈이 호흡기관에 주는 선량을 측정 평가할 목적으로 CR-39 비적검출기를 내장한 라돈컵을 사용하여 대기중 라돈농도를 측정하였다. 직접헝 검출기 및 개방 컵과 필터 컵의 구조를 갖는 CR-39 비적검출기에 대한 라돈검출인자는 공기중의 농도가 잘 알려진 표준라돈 조사시설에서 이들 검출기와 라돈컵을 일정기간 조사하여 결정하였다. CR-39를 $70^{\circ}C$, 30% NaOH 용액으로 220분간 화학부식하였을 때 직접형 검출기와 개방 컵, 필터 컵에 대한 라돈검출인자는 각각 0.273, 0.0813, 0.0371 tr $mm^{-2}/(37\;Bqm^{-3}{\cdot}d)$였다. 또한 1988년 5월에서 1989년 3월까지 대전(충남대학교)에서 측정한 대기중의 라돈농도는 개방 컵에 의한 결과는 27.4 - 135.8 $Bq/m^3$ (0.74 - 3.67 pCi/l)로서 연평균 73.3Bq/$m^3$ (1.98pCi/l)이었으며, 필터 컵에 의한 결과는 16.7 - 143.9 Bq/$m^3$ (0.45 - 3.89pCi/l)로 연평균 68.5 Bq/$m^3$ (1.85 pCi/l)이었다. 측정한 옥외 대기중의 라돈농도와 부위별 폐선량모형으로 부터 산출한 ICRP 표준인의 호흡기관에 대한 실효 선량당량률은 약 520 nSv/h로 평가되었다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2002년도 제3회 최신 분말제품 응용기술 Workshop
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• pp.133-155
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• 2002

1. Quasicrystalline powders shows exotic physical and mechanical p properties 2. Applications: structural application: strengthening particles for composites C Coating application: wear resistance, low friction coefficient 3. For thermal spaying: material loss during process should be c considered to control chemical composition of deposit 4. Friction coefficient is strongly dependent on contact geometry F Friction coefficient from pin on plate: 0.1-0.2 Friction coe야icient from flat on plate: about 0.46. 5. Quasicrystalline materials show lower friction coefficient but higher w wear rate than corresponding values of $Cr_20_3$ coated layer. 6. Amorphous coating seems to be promising

• 한국안전학회지
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• 제21권1호
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• pp.28-34
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• 2006

A procedure of estimating failure probability is demonstrated for a pressurized pipe of CrMo steel used at $538^{\circ}C$. Probabilistic fracture mechanics were employed considering variations of pressure loading, material properties and geometry. Probability density functions of major material variables were determined by statistical analyses of implemented data obtained by previous experiments. Distributions of the major variables were reflected in Monte Carlo simulation and failure probability as a function of operating time was determined. The creep crack growth life assessed by conventional deterministic approach was shown to be conservative compared with those obtained by probabilistic one. Sensitivity analysis for each input variable was also conducted to understand the most influencing variables to the residual life analysis. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• 대한기계학회논문집
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• 제18권12호
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• pp.3195-3201
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• 1994

In order to analytically predict tapping torque and thrust force in high speed tapping, a cutting model for main cutting edge with a uniformly restricted tool-chip contact area were developed. From this model equations are derived for the prediction of tapping torque given the cutting conditions, tap geometry, and an empirical factor which is related to the workmaterial. Computed values of torque is shown to compare favorably with those obtained from tapping tests on 16MnCr5. The applied torque about the cutting edge of teeth at lead chamfer is estimated respectively and it is shown that observed value is gradually decreased with following teeth.

• Journal of Mechanical Science and Technology
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• 제15권10호
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• pp.1417-1422
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• 2001

Since fracture surface presents clear evidence to describe the circumstances of material failure event, analysis of fracture surface should provide plenty of useful information for failure prevention. Thus if we extract proper information from the fracture surface, the safety evaluation, for plant component could be more accurate. In general, the chaotic morphology of fracture surface is determined by the degree of material degradation as well as by other factors such as type of load, geometry of specimen, notch condition, microstructure of material and environment. In this research, we developed a fractal analysis technology for the fracture surface of aged turbine rotor steel based on the slit-island technique using an image analyzer. Moreover the correlation between the fractal dimension and the aging time was studied.

• Bulletin of the Korean Chemical Society
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• 제15권2호
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• pp.145-150
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• 1994

The low temperature luminescence and excitation, room-temperature UV-visible and infrared spectra of [Cr(${\pm})chxn_3]Cl_3$ (chxn=trans-1,2-cyclohexanediamine) have been measured. It is found that the zero-phonon line in the excitation spectrum splits into two components by $47\;cm^{-1}$. The eight electronic transitions due to spin-allowed and spin-forbidden are assigned. As expected, nitrogen atoms of chxn ligand have strong ${\sigma}-donor $properties toward chromium(Ⅲ). The positions and splittings of sharp-line transitions are analyzed as a function of the Cartesian bite (${\alpha}$) and twist (${\beta}$) angles to predict the metal-ligand geometry.

• Journal of Welding and Joining
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• 제27권5호
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• pp.49-54
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• 2009

Recently, a demand of ferritic STS is increasing rapidly in automobile exhaust system. Exhaust manifolds are the part nearest to the engine so that the material is exposed to high temperature exhaust gas. Excellent heat resistant properties, especially high temperature strength, thermal fatigue resistance and high corrosion resistance are necessary for these parts. STS429L contains 15 weight percent of Cr and low Mo, so has good price competitive. And it has excellent high temperature strength and corrosion resistance, so receives attentions as material that applying to exhaust manifold. In tensile test of lap joint welded STS 429L, most of specimens are failed in base metal, but occurs brittle fracture in weld metals at some specimens in the face of good welding conditions. In the process of tensile test, lap joint welded STS429L specimens are transformed locally. The brittle fracture occurs that local transforming area exists in weld metals. But, butt welding specimens made by same materials showed ductile fracture in tensile test and bending test. In this study, suppose the reason of brittle fracture is in the combined local transform and tensile stress, through analysis of bead geometry, evaluate geometrical factor of brittle fracture in lap joint welded STS429L.