• 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.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.208-212
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• 2010

The high-speed railway consists of tracks, gravel ballast and subgrade, and the dynamic load is passed to subgrade through track and gravel ballast. The relaxation condition of the gravel ballast is able to be evaluate relatively and to be repaired through a continuous management, but it is difficult to evaluate the condition of subgrade, which is final part of supporting dynamic load and to repair it when made a problem. The gravel ballast and subgrade are evaluated by determining shear wave velocity. To evaluate ballast and subgrade, a good method to determine shear wave velocity is a non-destructive experiment such as surface wave tests providing a prompt experiment because an experiment in railway has a lot of tests which are carried out following railway directions and needs to prevent damage of the system. In general, a railway has limitation of an experimental space by narrow width, sleeper and etc., and background noise by a reflector exists. The existing surface wave tests need a minimum space, and it is difficult to get a reliable test results on account of background noise effect. Therefore, it is difficult or impossible to apply to existing surface wave test of subgrade and ballast. In this study, the HWAW method is applied to determine a shear wave velocity profile of the underground. The HWAW method is the experiment which is able to be carried out on a narrow space, and it determines share wave velocity of a site by measuring the wave from surface sources on the same spot. In addition, it removes effects of background noise accordingly to a signal processing using harmonic wavelet transforms, so it is useful to evaluate subgrade of a high-speed railway in the narrow space and the situation of background noise. In order to check an application of the HWAW method, an experiment is carried out on a high-speed railway field and a test result is compared to boring results.

• Journal of Welding and Joining
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• 제20권5호
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• pp.72-77
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• 2002

Flip-chip interconnection that uses solder bump is an essential technology to improve the performance of microelectronics which require higher working speed, higher density, and smaller size. In this paper, the shear strength of Cr/Cr-Cu/Cu UBM structure of the high-melting solder b01p and that of low-melting solder bump after aging is evaluated. Observe intermetallic compound and bump joint condition at the interface between solder and UBM by SEM and TEM. And analyze the shear load concentrated to bump applying finite element analysis. As a result of experiment, the maximum shear strength of Sn-97wt%Pb which was treated 900 hrs aging has been decreased as 25% and Sn-37wt%Pb sample has been decreased as 20%. By the aging process, the growth of $Cu_6Sn_5$ and $Cu_3Sn$ is ascertained. And the tendency of crack path movement that is interior of a solder to intermetallic compound interface is found.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 추계학술대회 초록집
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• pp.179-180
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• 2009

본 연구에서는 ENIG, ENEPIG 의 Pad 표면처리가 고속전단시험에 미치는 영향에 대해 연구하고자 하였다. Pad의 표면처리를 ENIG와 ENEPIG로 하여 고속전단시험을 수행하여 그에 따른 Shear force와 Shear energy를 측정하였다. 고속전단시험결과 ENEPIG 표면처리 시편이 ENIG의 표면처리시편보다 shear force와 shear energy의 값이 높게 나타났다.

• 한국전산구조공학회논문집
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• 제30권1호
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• pp.55-61
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• 2017

최근 콘크리트 궤도 슬래브 하면과 교량 바닥판 사이에 저마찰 슬라이드층을 형성하는 궤도 시스템인 슬라이딩 궤도와 관련된 연구가 활발히 진행되고 있다. 본 연구에서는 슬라이딩 궤도에서 열차 주행에 따른 횡방향 하중을 저항하기 위해 설치되는 횡방향 지지 콘크리트 블록의 전단 내하력에 대한 연구를 수행하였다. 횡방향 지지 콘크리트 블록의 전단 내하력 산정을 위해 타설경계면에서의 콘크리트 마찰 및 철근의 다월 거동을 고려한 산정 기법을 개발하다. 제안된 산정 기법은 기존의 실험에서 측정된 전단 내하력을 13~23% 정도 보수적으로 예측하는 것으로 나타났다. 이는 균열면 골재 맞물림 효과를 무시한 것에 따른 것으로, 현장에서의 타설경계면 상태가 불확실한 것을 고려할 때 횡방향 지지 콘크리트 블록에 대한 안전측 설계를 위해 제안된 산정 기법이 합리적인 것으로 판단된다. 제안된 전단 내하력 산정 기법을 토대로 횡방향 지지 콘크리트 블록에 대한 설계 방안을 마련하였다.

• 한국철도학회논문집
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• 제17권1호
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• pp.43-51
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• 2014

철도에서 토공구조물은 입경이 큰 조립지반재료를 주요한 재료로 사용하고 있다. 그러나 이들 재료에 대한 미소변형 거동을 평가할 수 있는 동적물성 산정에 대한 연구는 대형시험장비의 부족으로 거의 이루어지지 않고 있다. 이에 본 연구에서는 국내 철도설계기준에 제시되어 있는 입도분포, 단위중량 등의 기본 조건에 맞는 강화노반(보조도상, 입도조정층), 접속부 자갈재료, 상부노반재료에 대해 대형반복삼축압축시험을 수행하여 저변형률 수준에 따른 정규화전단탄성계수와 감쇠비곡선을 제안하고, 각 재료별로 수식 모델과 계수를 제시하였다.

• Smart Structures and Systems
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• 제30권5호
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• pp.479-500
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• 2022

In this study, a new type of isolation bearing is proposed by combining S-shaped steel plate dampers (SSDs) with a spherical steel bearing, and the seismic control effect of a five-span standard high-speed railway bridge is investigated. The advantages of the proposed S-shaped steel damping friction bearing (SSDFB) are that it cannot only lengthen the structural periods, dissipate the seismic energy, but also prevent bridge unseating due to the restraint effectiveness of SSDs in the large relative displacements between the girders and piers. This study first presents a detailed description and working principle of the SSDFB. Then, mechanical modeling of the SSDFB was derived to fundamentally define its cyclic behavior and obtain key mechanical parameters. The numerical model of the SSDFB's critical component SSD was verified by comparing it with the experimental results. After that, parameter studies of the dimensions and number of SSDs, the friction coefficient, and the gap length of the SSDFBs were conducted. Finally, the longitudinal seismic responses of the bridge with SSDFBs were compared with the bridge with spherical bearing and spherical bearing with strengthened shear keys. The results showed that the SSDFB can not only significantly mitigate the shear force responses and residual displacement in bridge substructures but also can effectively reduce girder displacement and prevent bridge unseating, at a cost of inelastic deformation of the SSDs, which is easy to replace. In conclusion, the SSDFB is expected to be a cost-effective option with both multi-stage energy dissipation and restraint capacity, making it particularly suitable for seismic isolation application to high-speed railway bridges.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.229-234
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• 2003

As electrorheological fluid(ER fluid) has a characteristic that apparent viscosity varies when electric field applied, so rheological characteristic(yield stress & viscosity) changes in proportion to the electric field applied and the response time is very short within a few miliseconds . In case of using ER fluid for journal bearing as lubricant, it is estimated that it's possible to realize very effective journal bearing system that is not complicate and has a very quick response time. It is necessary to examine the influence of rheological characteristic that varies with electric field applied on bearing characteristic to apply ER fluid to journal bearing, however there are few studies for about that. As for the journal bearing, it comes under high shear flow mode that has shear rate range of $10^3\~10^4s^{-1}$ because rotational speed is very high and clearance is small. But most of the studies for about ER fluid issued until now is about the range of $10\~10^2s^{-1}$. So, there are a lot of difficulties to understand the characteristic offish shear flow mode and furthermore it is restricted to make an experiment for about the characteristic of ER fluid because of the limitation of experimental equipment. The equipment was prepared to make an experiment lot high shear flow mode that has the range of $10^3\~10^4s^{-1}$ using ER fluid that is composed of silicon oil with dispersed particle of starch. Using the above system, the fluid characteristic of ER fluid was studied.

• Steel and Composite Structures
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• 제22권5호
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• pp.1019-1038
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• 2016

The use of high-strength concrete (HSC) in precast concrete segmental bridges (PCSBs) can minimize the superstructure geometry and reduce beam weight, which can accelerate the construction speed. Dry joints between the segments in PCSBs introduce discontinuity and require special attention in design and construction. Cracks in dry joints initiate more easily than those in epoxy joints in construction period or in service. Due to the higher rupture strength of HSC, the higher cracking resistance can be achieved. In this study, shear behavior of dry joints in PCSBs was investigated by experiments, especially focusing on cracking resistance and shear strength of HSC dry joints. It can be concluded that the use of HSC can improve the cracking resistance, shear strength, and ductility of monolithic, single-keyed and three-keyed specimens. The experimental results obtained from tests were compared with the AASHTO 2003 design provisions. The AASHTO 2003 provision underestimates the shear capacity of single-keyed dry joint C50 and C70 HSC specimens, underestimates the shear strength of three-keyed dry joint C70 HSC specimens, and overestimates the shear capacity of three-keyed dry joint C50 HSC specimens.

• Tribology and Lubricants
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• 제16권4호
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• pp.289-294
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• 2000

This paper present the contact stresses, which considers the shear stress at the cam and follower interface in the direct acting type valve train system of a high speed engine. To determine the contact condition, the normal contact forces are calculated by using the lumped mass dynamic modeling. The line contact is considered between the cam and follower interface. The variations of dynamic stresses are presented as a function of camshaft rotational angle. Also the effects of various design parameters are investigated.