• 대한기계학회논문집
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• 제12권2호
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• pp.278-285
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• 1988

본 연구에서는 SM15C재와 SM35C재에 퍼얼라이트, 페라이트 조직의 영향을 배재한 비교적 균질한 조직인 구상화시멘타이트조직과 SM35C재에 실용조직 이면서 비교적 균질한 조직인 마르텐사이트 조직을 만들고, 가공하였다.

• Bulletin of the Korean Chemical Society
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• 제30권2호
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• pp.315-318
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• 2009

Some particular bound state energies of an electron, under Coulomb potential field, confined in a two-dimensional circle and a three-dimensional sphere are analytically derived. The derivation shows that the electron cannot be bound in a negative energy state when the circle (or sphere) is smaller than a certain critical size. The critical size dependency on the strength of Coulomb potential and the angular momentum of the electron is also analytically derived. This system mimics quantum dots. Therefore the derivation provides new information on a minimum critical size of quantum dots with hydrogenic impurity.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.395-401
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• 2003

In this paper, the dent printing phenomena and critical dent size which lead to premature failure of deep grooved ball bearing for automobiles are presented. The results of newly assembled test bearings showed that the ball dent size strongly affect the bearing life and inner ring raceways were the major failed parts in spite of using the dented balls. The dent printing phenomena are a root cause of premature failure, which was not reported until now. And there exist the critical ball dent size for given rolling bearings and operating conditions. So, the initial condition of tribologically mating parts should be treated as important as the failed body itself.

• 대한기계학회논문집B
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• 제23권3호
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• pp.398-407
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• 1999

In the present image processing technique, the concept of the gradient indicator(GI) has been introduced to find out the depth-of-field in sizing large particles ranging from $30{\mu}m$ to $30{\mu}m$ where using of the concept of the normalized contrast value(VC) is not appropriate. The gradient indicator is defined as the ratio of the local value to the maximum possible value of the gray-level gradient in an image frame. The gradient indicator decreases with the increases of the particle size and the distance from the exact focal plane. A particle is considered to be in focus when the value of the gradient indicator at its image boundary stays above a critical value. This critical gradient indicator($GI_{critical}$) is defined as the maximum gradient indicator($GI_{max}$) subtracted by a constant ${\Delta}GI$ which is to account for the particle-size effect. In the present ca.so, the value of ${\Delta}GI$ was set to 0.28 to keep the standard deviation of the measured particles mostly within 0.1. It was also confirmed that, to find the depth-of-field for small particles(${\leq}30{\mu}m$) with the same measurement accuracy, tho concept of the critical normalized contrast($VC_{critical}$) is applicable with 85% of the maximum normalized contrast value($VC_{max}$). Finally, the depth-of-field was checked for the size range between $10{\mu}m$ and $300{\mu}m$ when the both in-focus criteria ($GI_{critical}$ and $VC_{critical}$) were adopted. The change of the depth-of-field with the particle size shows good linearity in both the VC-applicable and the GI-applicable ranges with a reasonable accuracy.

• 한국분말재료학회지
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• 제13권5호
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• pp.360-365
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• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

• Communications for Statistical Applications and Methods
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• 제17권6호
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• pp.791-801
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• 2010

마이크로데이터 제공시 발생될 수 있는 노출(disclosure)과 노출위험을 나타내는데 사용되는 측도인 유일성(uniqueness) 그리고 모집단 유일성의 개수를 추정하기 위한 초모집단 모형으로 Multinomial-Dirichlet 모형, Takemura의 Poisson-Gamma 모형, Modified Multinomial-Dirichlet 모형, Bethlehem의 Poisson-Gamma 모형을 다룬다. 이 4개의 모형에 대해 마이크로데이터 제공에 따른 임계모집단 크기(critical population size)를 결정한다.

• 한국표면공학회지
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• 제35권3호
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• pp.165-171
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• 2002

TiN coating were deposited onto different WC-Co substrates using arc ion plating (AIP) technique. The structure and morphology for the deposited coating were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The adhesion behavior of the deposited TiN coating was investigated with a conventional scratch test. Effects of WC particle size and Co content on the adhesion strength between the deposited TiN coating and substrate were studied. During the scratch test, the value of critical load was dependent of WC particle size and Co content on substrate. As the WC particle size and Co content on substrate decreased, the critical load increased. The highest critical load, approximately 110N, was obtained at WC particle size of 1$\mu\textrm{m}$ and Co content of 10wt.%.

• 오토저널
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• 제11권1호
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• pp.51-56
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• 1989

This study was performed to investigate the effect of defect on fatigue strength under the stress of rotary bending. The specimens were made of low carbon steel having artificial microholes, namely, single micro-hole and two adjacent micro-holes as natural defects, and the effects of the diameter of hole and the distance between the holes on fatigue strength have been investigated. The obtained result can be summarized as follows: 1, The critical defect means the largest size of defect that does not affect fatigue limit, and correspondes to the size of defect leading to final fracture under fatigue limit of smooth specimen. The size of defect which has an effect on fatigue limit is larger than that of critical defect. 2, The defect larger than the critical defect affects fatigue strength for as a kind of size effect, and the physical meaning of size effect of defect is considered same as the one of notch effect.

• 한국정밀공학회지
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• 제25권6호
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• pp.116-125
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• 2008

In general, fretting is a contact damage process due to micro-slip associated with small amplitude oscillatory movement between two surfaces in contact. Previous studies in fretting fatigue have observed a contact size effect related to contact width. The volume-averaging method of theoretically predicted contact stress fields was required to emulate experimental trends and to predict the observed contact size effects. This contact size effect is captured by the mean values of stresses and strains at the element integration points of FE model and two critical plane models (SWT, FS) in the present paper. It is shown that crack nucleation and fretting fatigue life can be predicted by the FE-based critical plane models.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2638-2651
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• 2020

Nozzle corner cracks present at the intersection of reactor pressure vessels (RPVs) and inlet or outlet nozzles have been a persistent problem for a number of years. The fracture analysis of such nozzle corner cracks is very important and critical for the efficient design and assessment of the structural integrity of RPVs. This paper aims to perform an engineering critical assessment of RPVs with nozzle corner cracks subjected to several transients accompanied by pressurized thermal shocks. The critical crack size of the RPV model with nozzle corner cracks under transient loading is evaluated on failure assessment curve. In particular, the influence of cladding on the crack initiation of nozzle corner crack under thermal transients is studied. The influence of primary internal pressure and secondary thermal stress on the stress field at nozzle corner and SIF at crack front is analyzed. Finally, the influence of different crack size and crack shape on the final critical crack size is analyzed.