• Tribology and Lubricants
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• 제26권1호
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• pp.1-6
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• 2010

In the last decade, laser surface texturing (LST) has emerged as a viable option of surface engineering. Many problems related with mechanical components such as thrust bearings, mechanical face seals and piston rings, etc, LST result in significant improvement in load capacity, wear resistance and reduction in friction force. It is mainly experimentally reported the micro-dimpled bearing surfaces can reduce friction force, however, precise theoretical results are not presented until now. In this paper, a commercial computational fluid dynamics(CFD) code, FLUENT is used to investigate the lubrication characteristics of a parallel thrust bearing having 3-dimensional micro-dimple. The results show that the pressure, velocity and density distributions are highly affected by the location and number of dimple. The numerical method and results can be use in design of optimum dimple characteristics, and further researches are required.

• International Journal of Precision Engineering and Manufacturing
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• 제1권1호
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• pp.42-48
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• 2000

Friction in bearing exerts an important effect upon power dissipation and heat generation of spindle system. This paper presents frictional moments derived from rotational axis coordinate system of spindle and frictional characteristics to spindle speed A frictional moment of spindle bearings is derived by work-energy method. Differential sliding moments in outer raceway has a major effect upon frictional resistance; spin sliding moments in inner raceway has a secondary effect. As spindle speed increases, also the frictional moments increase. In high-speed region, ceramic ball bearing 몬 smaller frictional moment than steel ball bearing.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제28회 추계학술대회
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• pp.221-226
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• 1998

The processing conditions for the mass production of platelet WS$_2$ lubricant powder were optimized. The mixture of tungsten and sulfur powders was sealed in a vacuum of 10$^{-3}$ torr and heat-treated at 850$\circ$C for 2 h. The internal pressure of reaction chamber was maintained at certain level by controlling the release valve automatically. The reaction product was the platelet WS$_2$ powder with an average size of 15 $\mu$m. The synthesized WS$_2$ powder was then coated on the wiper-blade of automobiles and the commercial deep-grooved ball bearing using wet and dry coating methods, respectively. High lubricity and wear resistance of wet coated wiper-blade were confirmed by the life test of 70,000 cycles. The life-time of the ball bearing assembled after WS$_2$ coating onto each part increased 50 times compared to the non-coated ball bearing.

• Steel and Composite Structures
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• 제9권2호
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• pp.173-189
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• 2009

This paper presents a study on the behavior and design of bolted stainless steel plates under in-plane tension. Using an experimentally validated finite element (FE) program strength of stainless steel bolted plates under tension is examined with an emphasis on plate bearing mode of failure. A numerical parametric study was carried out which includes examining the behavior of stainless steel plate models with various proportions, bolt locations and in two different material grades. The models were designed to fail particularly in bolt tear-out and material piling-up modes. In the numerical simulation of the models, non-linear stress-strain material behavior of stainless steel was considered by using expressions which represent the full range of strains up to the ultimate tensile strain. Using the results of the parametric study, the effect of variations in bolt positions, such as end and edge distance and bolt pitch distance on bearing resistance of stainless steel bolted plates under in-plane tension has been investigated. Finally, the results obtained are critically examined using design estimations of the currently available international design guidance.

• 열처리공학회지
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• 제8권3호
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• pp.205-212
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• 1995

Effect of Mn addition on rolling contact fatigue of C-base induction hardened bearing steels has been investigated to develop inexpensive surface-hardened bearing steels with improved resistance to rolling contact fatigue. Fatigue tests were conducted in elasto-hydrodynamic lubricating conditions at a shaft speed of 5,000rpm, under max. Hertzian stress of $492kg/mm^2$. It was found in the C-Mn steels that effective depth of induction hardened layer and amount of retained austenite were slightly increased in comparison with those of C-base steels. finer interlamellar spacing of pearlite in the C-Mn steels was also observed using TEM. Decomposition of retained austenite during rolling contact fatigue was smaller in quantity in the C-Mn steels than C-base steels. This might be associated with enhanced mechanical stability of retained austenite with addition of Mn. Statistical analysis of fatigue life for C-Mn steels using Weibull distribution indicated that improved resistance to rolling contact fatigue was mainly attributed to transformation induced plasticity and mechanical stability of retained austenite.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.455-465
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• 2008

In this study, the load distribution and deformation of rock-socketed drilled shafts subjected to axial load are investigated based on small scale model tests. In order to analyze the effects of major influencing factors of end bearing capacity, Hoek-cell triaxial tests were performed. From the test results, it was found that the initial slope of end bearing load transfer (q-w) curve was highly dependent on rock mass modulus and pile diameter, while the ultimate unit toe resistance ($q_{max}$) was influenced by rock mass modulus and the spacing of discontinuities. End bearing load transfer function of drilled shafts socketed in rock was proposed based on the Hoek-cell triaxial test results and the field loading tests which were performed on granite and gneiss in South Korea. Through the comparison with pile load tests, it is found that the load-transfer curve by the present study is in good agreement with the general trend observed by field loading tests, and thus represents a significant improvement in the prediction of load transfer of drilled shaft.

• Structural Engineering and Mechanics
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• 제84권2호
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• pp.225-238
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• 2022

In order to improve the cracking resistance of reinforced concrete and give full play to the advantages of prefabricated assembly structure in construction, prestressed reinforced concrete composite beam (PRCC) is proposed. Through the bending static test of seven I-shaped beam specimens, the bending failure modes and bearing capacity of PRCC and reinforced concrete composite beam are compared and analyzed, and the effects of prestress size, prestressed reinforcement layout and prestress application sequence on the flexural behavior of PRCC beams are studied. The results show that the cracking load and ultimate load of PRCC beams significantly increased after prestressing, and prestressed tendons can effectively control the crack development. With the increase of prestressing degree, the deformation resistance and bending stiffness of PRCC beams are increased. The application sequence of prestress has little influence on the mechanical properties of PRCC beams. The crack width, stiffness and normal section bearing capacity of PRCC beam are analyzed, and the calculated results are in good agreement with the experimental results.

• 콘크리트학회논문집
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• 제24권2호
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• pp.129-136
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• 2012

철근 압축이음은 초고층 건축물의 수직 부재에서 거의 모든 층에서 발생되므로, 압축이음 거동에 대한 명확한 이해는 합리적인 이음부 설계에 필수 요소가 된다. 이 연구에서는 압축을 받는 철근이음의 인자별 특성을 분석하기 위해, 부착 또는 지압만 존재하는 압축이음 실험을 수행하였다. 실험 결과 부착과 지압이 함께 존재하는 일반이음에서는 부착과 지압의 상호 간섭으로 각각의 고유 강도가 100% 발현되지는 않았다. 특히 지압은 국부적인 영역에서 발현되므로 중첩으로 인한 감소량이 부착에 비해 컸다. 부착과 지압이 함께 존재하는 일반이음은 부착이음과 지압이음에 비해 동일하중에서 콘크리트와 철근의 상대변위를 줄일 수 있다. 이음 파괴는 콘크리트와 철근 사이의 과도한 상대변위로 인해 발생되므로 일반이음의 강도가 부착이음과 지압이음에 비해 항상 높아진다. 따라서 부착 또는 지압을 제거함으로써 압축이음강도를 향상시킬 수는 없다. 또한 부착이음에서 순수 부착강도는 인장이음의 부착강도와 거의 유사하게 나타났으므로, 압축이음강도가 인장이음강도보다 큰 것은 지압의 영향임을 알 수 있다.

• Structural Engineering and Mechanics
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• 제49권3호
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• pp.395-410
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• 2014

Fiber Reinforced Elastomeric Bearings (FREBs) are a relatively new type of laminated bearings that can be used as seismic/vibration isolators or bridge bearings. In an unbonded (U)-FREB, the bearing is placed between the top and bottom supports with no bonding or fastening provided at its contact surfaces. Under shear loads the top and bottom faces of a U-FREB roll off the contact supports and the bearing exhibits rollover deformation. As a result of rollover deformation, the horizontal response characteristics of U-FREBs are significantly different than conventional elastomeric bearings that are employed in bonded application. Current literature lacks an efficient analytical horizontal stiffness solution for this type of bearings. This paper presents two simplified analytical models for horizontal stiffness evaluation of U-FREBs. Both models assume that the resistance to shear loads is only provided by an effective region of the bearing that sustains significant shear strains. The presented models are different in the way they relate this effective region to the horizontal bearing displacements. In comparison with experimental results and finite element analyses, the analytical models that are presented in this paper are found to be sufficiently accurate to be used in the preliminary design of U-FREBs.

• 한국구조물진단유지관리공학회 논문집
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• 제12권4호
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• pp.123-132
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• 2008

스톤컬럼 공법의 침하량 저감과 지지력 증진 효과를 파악하고자 연약한 준설매립 지반에 쇄석재료와 슬래그 재료를 이용하여 시험시공 후 지하수위계측 및 현장시험을 진행하였다. 현장실험 결과, 지지력 증진 및 침하량 저감 효과가 파악되었으며 상재하중 없이도 지하수위는 저하되는 양상을 보였다. 이는 스톤컬럼 공법이 밀도증가 측면과 더불어 액상화 저항에 우수함을 나타낸다. 일반적인 이론식을 이용하여 원지반 및 복합지반에 대한 침하량과 지지력 산정 결과, 스톤컬럼 공법은 2.7~5.7배의 지지력 증진 효과와 2~3.5배의 침하량 저감 효과가 있는 것으로 판단되었다.