• 한국정밀공학회지
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• 제28권6호
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• pp.745-750
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• 2011

In a hope to better understand the flow and convective heat transfer characteristics inside a ball bearing, air flow between the rolling elements and raceways at high speed bearing rotation is numerically investigated using a simplified inner geometry of bearing and a CFD technique. Flow simulation results reveal the pressure distribution of airflow and the shear stress distribution on the ball surface, of which nonuniformity becomes significant with the increasing rotational speed. Also, the local point of maximum shear stress coincides with the stagnation flow area on the surface of rolling elements. A complex pattern of three-dimensional vortex structures is found in the air flow due to the relative motion of bearing elements and three different types of vortex pairs exist around the rotating and orbiting rolling elements.

• 한국지반공학회지:지반
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• 제14권4호
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• pp.117-128
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• 1998

지오그리드를 이용한 입체적인 매트리스기초는 연약지반의 지지력을 증가시키기 위해서 증증 사용되며 그 효과를 인정받고 있다. 지오그리드-매트리스 시스템이란 그 자체의 강성에 의해 하중을 보다 더 넓게 기초지반에 분산시킴으로서 지지력의 증대효과 및 침하억제효과를 가져오는 공법이다. 그러나, 이에 대한 메카니즘은 아직 명확하게 규명되어 있지 않다. 본 연구에서는 지오그리드 매트리스기초 아래 전파응력분포 특성을 파악하기 위해 모형실험을 실시하였고, 실험에서는 지오그리드 매트리스기초와 두께 및 지지하는 기초의 강성 등을 영향인자로서 고려하였다. 실험결과로부터 매트리스기초하의 전파응력분포 특성을 파악하였고, 지오그리드 매트리스기초 설계시 지지력을 구할 수 있는 방법을 제안하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.430-440
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• 2009

Top-Base Foundation(TBF) was developed in Japan as a factory made concrete product. It is actively used in 6,000 sites by the end of 1980s in Japan and applied for a domestic patent in 1985. It is a shallow foundation whose effectiveness is proven by many relevant researchers and engineers. TBF was introduced to Korea in 1991 and has been applied mainly to architectural structures to date. Currently, the effectiveness in bearing capacity and settlement of TBF is being underestimated for civil engineering structures. Characteristics of Top-Base Foundation studied in Japan and Korea is known as follows: (1) as concrete part and crushed stone behave together, they perform the function of rigid mat; (2) the conical part and pile part of TBF disperses load by interaction with the crushed stone; (3) by preventing lateral strain and differential settlement on lower ground, it improves bearing capacity and constrains settlement at the same time. In Korea, it is used mostly in clayey soft grounds. The formula of bearing capacity and settlement of TBF suggested in Japan give the values of the underestimated. bearing capacity while its settlement is overestimated in comparison with the values measured from the field loading test. Therefore, in this study, the stress delivery mechanism of Top-Base Foundation developed in Japan and Floating Top Base developed in Korea is investigated through numerical analysis and laboratory model test.

• 한국철도학회논문집
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• 제10권2호
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• pp.186-194
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• 2007

This study was performed to compare the load-carrying capacities of the reinforced concrete structure between the carbon fiber adhesion reinforcement method and the external post-tensioning method and further estimate the effective stress of the reinforced material by analyzing the experimental reinforcing effect of each method and the behavior resulting from each method. As a result, it was found out that the effective stress of the carbon fiber reinforcement according to the carbon fiber adhesion reinforcement method had an unexpected value, and also, bearing of the stress was found to be far from sharing thereof. That is to say, while the carbon fiber was bearing the whole stress to some limits, it got to be momentarily ruptured as soon as it went beyond such limits. On the other hand, the external post-tensioning method has the advantage of inducing an initial effective stress by introducing a strain, and thus, it was found that behavior or bearing of the stress was also found to be a solid behavior of the steel wire. This method was also found to be more efficient and excellent than the carbon fiber adhesion reinforcement method in the reinforcing effect or securing the effective stress. Accordingly, we were to discuss the effective stress as comparatively examined, focusing on deriving of the more enhanced reinforcing effect on the basis of the experiment to which the field characteristic is added.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.613-614
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• 2012

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.481-488
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• 1998

Elastomeric bearing is used as one of the most useful way for isolation structures, because the horizontal stiffness is much lower than the vertical stiffness. In the design criteria of Elastomeric bearing, the stability of the bearings is evaluated by shear strain due to compression, lateral displacement, and rotation. The question how soft rubber can sustain heavy structure is now able to be solved by Ultimate capacity test of Laminated Elastomeric Bearings, which results 1,200kg/$\textrm{cm}^2$ of the max. compressive stress and this shows what a sufficient safety factor Elastomeric bearing has !

• Tribology and Lubricants
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• 제18권3호
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• pp.187-193
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• 2002

The half-value breadth off-ray diffraction profile line is generally used for a factor in nondestructive hardness measuring method of steel. In this paper, the problem in using the half-value breadth for the hardness measuring method is evaluated in strain hardened steel. And new hardness measuring method using residual stress is proposed X-ray diffraction test after rolling contact fatigue test of ball bearing with inner race of various hardness are carried out to measure the distribution of residual stress and half-value breadth from surface. The result of this study shows that there is little correlation between half-value breadth and hardness in the higher strength region and in the region increasing the hardness by strain hardening. But the magnitude of residual stress on/under race after rolling contact fatigue test becomes clearly to be correlative with hardness. Thus, it is concluded that the hardness of strain hardened steel can be estimated by this relationship between residual stress and hardness.

• Tribology and Lubricants
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• 제31권2호
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• 산업기술연구
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• 제22권A호
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• pp.145-151
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• 2002

This paper is results of extensive centrifuge model experiments about design factors influencing the bearing capacity and the settlement behaviors of SCP (Sand Compaction Pile). Centrifuge model tests were carried out changing design factors for SCP method such as replacement area ratio (as= 20, 40, 70%), Improvement ratio to footing width (W/B = 1, 2, 3), and amount of fines m sand pile (#200 = 5, 10, 15). Therefore, the effects of these design factors on the bearing capacity and the settlement behavior of SCP were investigated and changes of stress concentratio rato due to such an design factors were also investigated. Centrifuge model testing technique for preparing and installing centrifuge model of sand compaction pile, using freezing them, was also developed. As results of centrifuge model tests, more fines in sand compaction pile increases the bearing capacity of SCP. Optimum improvement ratio to footing width was found to be 2. Values of stress concentration ratio was in the ranges of 1.5 - 3.5. The depth of bulging in sand plies was found in the range of 2.0 - 2.5 times of pile diameter.

• 산업기술연구
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• 제22권B호
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• pp.191-197
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• 2002

This paper is experimental and numerical research results of performing centrifuge model tests to investigate the geotechnical engineering behavior of slag compaction pile as a substitute of sand compaction pile. In order to find the geotechnical engineering characteristics of the soft clay and the slag used in centrifuge model experiments, basic soil property tests, consolidation test, permeability tests and triaxial compression tests were performed. For centrifuge model tests, slags with changing relative density were used and their bearing capacity, stress concentrations in between pile and soft clay, settlement characteristics, and failure modes were investigated. As a results of centrifuge model tests, it was found that the bearing, capacity of model was increased with increasing density of slag pile and general shear failures were occured. Miniature soil pressure gauges were installed on model pile and soft ground respectively and thus vertical stress acting on them were measured. Stress concentration ratio was found to be in the range of 2.0~3.0. Bearing capacity obtained from the model test with slag was greater than that from the model test with a sand having the identical layout to each other. Thus it was confirmed the slag was an appropriate substitution of pile for sand.