• Tribology and Lubricants
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• 제34권4호
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• pp.146-159
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• 2018

This paper presents a wear analysis procedure for calculating the wear of journal bearings of a four-strokes and four-cylinder engine operating at a constant angular crank shaft speed during firing conditions. To decide whether the lubrication state of a journal bearing is in the possible region of wear scar, we utilize the concept of the centerline average surface roughness to define the most oil film thickness scarring wear (MOFTSW) on two rough surfaces. The wear volume is calculated from the wear depth and wear angle, determined by the magnitude of each film thickness on a set of oil films with thicknesses lower than the MOFTSW at every crank angle. To calculate the wear volume at one contact, the wear range ratio during one cycle is used. The total wear volume is then determined by accumulating the wear volume at every contact. The fractional film defect coefficient, asperity load sharing factor, and modified specific wear rate for the application of the mixed-elasto-hydrodynamic lubrication regime are used. The results of this study show that wear occurs only at the connecting-rod big-end bearing. Thus, simulation results of only the big-end bearing are illustrated and analyzed. It is shown that the wear volume of each wear scar group occurs consecutively as the crank angle changes, resulting in the total accumulated wear volume.

• 한국지진공학회논문집
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• 제16권1호
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• pp.27-35
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• 2012

이 연구에서는 추계학적 그린함수법에 의한 단층 모델을 이용하여 지진파를 합성하고 단층 파라미터의 변화에 의한 지반 운동의 차이를 평가하였다. 모멘트 규모 6.5의 단층을 예제로 선정하였고 아스페리티 면적의 통계값을 이용하여 슬립의 분포를 모델링하였다. 평가를 위해 고려된 단층 파라미터들은 진원의 위치, 전단파 속도 대비 파열 전파속도 비, 상승시간, 절점주파수 그리고 고주파감쇠 필터 등 이었다. 요소지진원에 적용된 파라미터들은 구조권역별 특성이 다른 지역의 값을 사용하였고 다른 파라미터들은 발생 가능한 임의의 값을 사용하였다. 생성된 지반운동 시간이력으로부터 응답스펙트럼을 작성하였으며, 파라미터의 값을 달리하여 비교하였다. 이로부터 각각의 단층파라미터에 의해 영향을 받는 주파수 구간 및 스펙트럼 가속도의 차이를 평가하였다.

• Tribology and Lubricants
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• 제32권4호
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• pp.132-139
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• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.

• 한국지반공학회논문집
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• 제20권1호
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• pp.5-12
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• 2004

본 연구는 암반에 근입된 현장타설말뚝의 화강암과 콘크리트의 부착면에서의 전단거동을 이해하려는 데 있다. 암반에 근입된 현장타설말뚝의 전단거동을 실내에서 실험하기 위해서는 현장에서의 전단거동을 모델링 해야 한다. 따라서, 말뚝의 축방향 대칭성을 고려해 암반에 근입된 전단면을 2차원으로 모델링함으로써 일정수직강성도(conctant normal stiffness; CNS) 조건의 전단시험을 실시할 수 있다. 본 논문에서는 국내 화강암을 대상으로 거칠기, 암의 강도, 응력경계조건 등을 고려하여 암-콘크리트 접촉부에 대한 일정수직강성도 전단시험을 수행하였다. 실험결과 각 변수(요철부의 경사각 및 높이, 수직강성도)에 따른 전단특성(첨두전단강도, 전단응력, 수직응력)은 물론 팽창현상(dilation) 등을 관찰할 수 있었다. 시험결과에 따르면 첨두 전단강도는 요철부의 경사각이 증가할수록, 그리고 수직강성도가 증가할 수록 증가하는 것으로 나타났으며, 팽창량은 요철부의 각도가 클수록 수직강성도가 작을수록 크게 나타났다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.255-256
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• 2002

In this paper, the frictional behavior according to the contact geometry was investigated using a micro-tribotester built inside a Scanning Electron Microscope (SEM) and an Atomic Force Microscope (AFM). FFT (Fast Fourier Transform) analysis for friction was conducted as a method to interpret the contact condition. From the experimental results, it could be concluded that the relative dimensions and distribution of contact asperities on the surface could be predicted by the power spectrum and main frequency in the FFT analysis of the friction signal.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.251-252
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• 2002

An algorithm has been developed to determine changes in surface topography on asperity level. The software stitches small but detailed images together to create one large image. If such an image is made before and after an experiment, their difference shows a direct 3D view of the changes in micro-geometry, rather than a change in surface parameters. The algorithm is described in detail and illustrated using artificial as well as real surfaces.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.229-230
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• 2002

This paper presents the hot spot behaviors on the rubbing surface of ventilated disk brake by using finite element method. The depth of asperities on the rubbing surface is usually $2-3\;{\mu}m$ so the real contact area is microscopically. Non-uniform contacts between the disk and the pads lead to high local temperatures, which may cause the material degradation, and develops hot spots, thermal cracking, and brake system failures at the end. High contact asperity flash temperatures in rubbing systems, which is strongly related to the hot spot. It was generally known that high temperature over about $700^{\circ}C$ may form martensite on the cast iron which is material for automotive disk brakes. In this paper, the contact stress, temperature distribution and strain have been presented for the specific asperities of real contact area microscopically by using coupled thermal-mechanical analysis technique.

• Tribology and Lubricants
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• 제25권5호
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• pp.342-347
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• 2009

This paper presents EHL analysis for rough surfaces with directional roughness. Three different types of surfaces with pure longitudinal roughness, pure transversal roughness and isotropic roughness are generated. For the surfaces with longitudinal and transversal roughness, two cases are analyzed; one is a case of asperity peak on a spherical contact center, the other one is of valley on a spherical contact center. As a results, the surface with pure transversal roughness gives higher pressure and smaller minimum film thickness than the surface with pure longitudinal roughness, and the surface with isotropic roughness has similar EHL behavior with the surface with pure transversal roughness.

• 한국세라믹학회지
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• 제43권7호
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• pp.415-420
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• 2006

The residual stresses in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloy samples using a Finite Element Method (FEM). It was found that the stress distribution of the interface boundary was dependent upon mainly the geometrical shape or its aspect ratio and the thickness of TGO layer, which was formed by growth and swelling behavior of oxide layer. Maximum compressive residual stress in the TBC/TGO interface is higher than that of the TGO/bond coat interface, and the tensile stress had nothing to do with change of an aspect ratio. The compressive residual stresses in the TBC/TGO and TGO/bond coat interface region increased gradually with the TGO growth.

• Tribology and Lubricants
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• 제16권6호
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• pp.415-424
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• 2000

The use of magnetoresistive (MR) head requires much tighter control of particle contamination in a drive since loose particles on the disk surface will generate thermal asperities (TA). In this study, a spinoff test was performed to investigate the adhesion and removal capability of a particle to disk surface. Numerical simulation was also performed to investigate dominant factor of particle detachment and to support experimental results. It was shown that particles are detached from the disk surface by the moment derived from the centrifugal force and the drag force and that the centrifugal force and capillary force are the dominant force, which determines spin-off of a particle on the disk surface. Removal of particles smaller than several micrometers, which are the main source of TA generation, is extremely difficult since the adhesion forces exceed the centrifugal force. Lubricant types and manufacturing process also influence the particle removal. Lower bonding ratio and lower viscosity of the lubricant will help to increase the removal rate of the particles from the disk surface.