• Tribology and Lubricants
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• 제16권3호
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• pp.201-207
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• 2000

The numerical procedure to analyze a non-steady 3-dimensional elastohydrodynamic lubrication on the cyclically loaded contact has been newly developed. The procedure was applied on the cam-roller contact of the valve mechanism for the marine diesel engine. Both the pressure distribution and the film thickness between the cam and roller follower were calculated for each time step of the whole cycle. The pressure spike is shown at the outlet of the roller edge and it is getting higher as the external load is increased. The film thicknesses in the result of the non-steady analysis have a tendency to increase compared to those in the result of the analysis with the assumption of steady state. Therefore, the surface roughness of the non-steady contact need not be limited below that of the steady contact of the equivalent operating conditions.

• Tribology and Lubricants
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• 제25권1호
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• pp.38-42
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• 2009

Gear is an essential component of an automotive. Crowning is used for tooth modification of a gear. The basic concept of gear tooth crowning is to reduce the stress concentration in edge of contact area and appropriate profile modifications can help gears to resist scoring, pitting, and tooth breakage. In this study, a method to determinate spur gear tooth crowning amount to make smooth surface stress and subsurface stress distribution is proposed. This method is based on the contact analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.616-621
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• 2005

Most machine element, such as gears and bearings, are operated in the mixed lubrication region. Contact between two asperities has an effect on machine life by increasing local pressure. To estimate fatigue lift exactly, asperity contact should be considered as a factor of fatigue liff because this happening produce friction, abrasion and make flash temperature. In this paper, asperity contact is considered as a result of film breakdown when lubricant pressure is not enough to separate two asperities. Contact pressure is calculated to asperity overlap region and added to lubricant pressure. For this model, numerical procedure is introduced and the result on surface roughness and velocity for wheel bearing is presented. Results of EHL analysis for wheel bearing show that asperity contact is occurred at the edge of EHL conjunction where has a insufficient lubricant pressure to separate two surface.

• Structural Engineering and Mechanics
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• 제44권1호
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• pp.61-72
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• 2012

The paper is on contact analysis of a spherical ball with a deformable flat, considering the effect of tangent modulus on the contact parameters of a non-adhesive frictionless elastic-plastic contact. The contact analysis of this model has been carried out using analysis software Ansys and Abaqus. The contact parameters such as area of contact between two consecutive steps, volume of bulged material are evaluated from the formulated equations. The effect of the tangent modulus is considered for determining these parameters. The tangent modulus are accounted between 0.1E and 0.5E of materials E/Y value greater than 500 and less than 1750. Result shows that upto an optimal tangent modulus values the elastic core push up to the free surface in the flat. The simulation is also carried out in Abaqus and result provide evidence for the volume of bulged material in the contact region move up and flow into the free surface of the flat from the contact edge between the ball and flat. The strain energy of the whole model is varied between 20 to 40 percentage of the stipulated time for analysis.

• 한국해양공학회지
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• 제18권5호
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• pp.36-42
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• 2004

Orthotropic laminates, such as [$0^{\circ}6$/$90^{\circ}6$]s and [$90^{\circ}6$/$0^{\circ}6$]s, were performed, using a commercial nonlinear finite element method. Interlaminar stress distributions, around the hole curve free-edge, were calculated. The delamination bearing strengths of pin joints were predicted, using the modified delamination failure criterion. These stress distributions were presented along the radial lines and around the free-edge of the hole. Further, three-dimensional non-linear contact analysis of orthotropic laminates was conducted to investigate the effect of friction. In this paper, laminates with a circular hole were taken to study interlaminar stresses the curved edge. This study may assist in the design of a thick composite laminate with mechanically pin joints.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2097-2107
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• 1996

The dynamic photoelastic technique had been utilized to investigate the possibillity of relieving the large local singular stresses induced at the corner of a right- angle- indenter. The indenter compressed a semi-infinite body dynamically with an impact load applied on the top of the indenter. The effects of the geometric changes of the indenter in terms of the diameter (d) and the location (1) of the stress relieving notch on the behavior of the dynamic contact stresses were investigated. The influence of stress relieving notches positioned along the edge of the semi-infinite body on the dynamic contact stresses were also studied by changing the diameter (D) and the location (L) of the notch. A multi-speak-high speed camera with twelve sparks were used to take photographs of full field dynamic isochromatic fringe patterns. The contact singular stresses were found to be released significantly by the stress relief notches both along the indenter and the edge of the semi-infinite body. The optimal position and geometry of the stress relieving notches were obtained with the aid of limited experimental results.

• 한국정밀공학회지
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• 제27권8호
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• pp.42-47
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• 2010

In this paper, the characteristics of contact surface damage due to fretting in a press-fitted shaft below the fretting fatigue limit are proposed by experimental methods. A series of fatigue tests and interrupted fatigue tests of small scale press-fitted specimen were carried out by using rotating bending fatigue test machine. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that fretting fatigue cracks were initiated even under the fretting fatigue limit on the press-fitted shafts by fretting damage. The fatigue cracks of press-fitted shafts were initiated from the edge of contact surface and propagated inward in a semi-elliptical shape. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. After steep increasing, the increase of wear rate is nearly constant under the load condition below the fretting fatigue limit. It is thus suggested that the fretting wear must be considered on the fatigue life evaluation because the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in the press-fitted structures.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.283-283
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• 2011

The n-doping effect by doping metal carbonate into an electron-injecting organic layer can improve the device performance by the balanced carrier injection because an electron ohmic contact between cathode and an electron-transporting layer, for example, a high current density, a high efficiency, a high luminance, and a low power consumption. In the study, first, we investigated an electron-ohmic property of electron-only device, which has a ITO/$Rb_2CO_3$-doped $C_{60}$/Al structure. Second, we examined the I-V-L characteristics of all-ohmic OLEDs, which are glass/ITO/$MoO_x$-doped NPB (25%, 5 nm)/NPB (63 nm)/$Alq_3$ (32 nm)/$Rb_2CO_3$-doped $C_{60}$(y%, 10 nm)/Al. The $MoO_x$doped NPB and $Rb_2CO_3$-doped fullerene layer were used as the hole-ohmic contact and electron-ohmic contact layer in all-ohmic OLEDs, respectively, Third, the electronic structure of the $Rb_2CO_3$-doped $C_{60}$-doped interfaces were investigated by analyzing photoemission properties, such as x-ray photoemission spectroscopy (XPS), Ultraviolet Photoemission spectroscopy (UPS), and Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a doping concentration at the interfaces of $Rb_2CO_3$-doped fullerene are changed. Finally, the correlation between the device performance in all ohmic devices and the interfacial property of the $Rb_2CO_3$-doped $C_{60}$ thin film was discussed with an energy band diagram.

• 한국컴퓨터정보학회논문지
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• 제28권12호
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• pp.33-40
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• 2023

한국이 초고령사회로 진입하면서 노인 복지에 대한 필요성이 증가하고 있으나 현재 복지 인력 부족이 사회문제로 대두되고 있다. 이에 대한 해결책으로 노인의 사회적 고립감 완화와 위급 상황 시 비상 연락 등의 기능을 하는 노인 돌봄 로봇이 활발히 연구되고 있다. 하지만 이러한 기능들은 사용자의 접촉이 있어야만 작동하여 기존 노인 돌봄 로봇의 한계점으로 자리 잡고 있다. 본 논문에서는 기존의 문제를 해결하기 위해 상용화된 노인 돌봄 로봇과 카메라를 통해 직접적인 접촉 없이도 사용자와 상호작용할 수 있는 돌봄 로봇 시스템을 제안한다. 돌봄 로봇에 연결된 엣지 디바이스에 표정 인식 모델과 행동 인식 모델을 탑재하였고, 공공데이터를 통해 모델의 학습 및 성능검증을 진행했다. 실험 결과를 통해 표정 인식과 행동 인식의 성능이 각각 정확도 96.5%, 90.9%인 것을 확인할 수 있으며, 수행 시간의 경우에는 각각 50ms, 350ms인 것을 확인할 수 있다. 해당 결과는 제안한 시스템의 표정 및 행동 인식 정확도가 높고 추론 시간이 효율적임을 확인하며, 이는 비접촉 상황에서도 원활한 상호작용을 가능하게 한다.

• 한국의류학회지
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• 제15권1호
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• pp.70-75
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• 1991

본 연구에서는 레이저광선의 투영을 이용한 접촉각측정기구가 개발되었다. 이 새로운 방법은 편평한 표면분만 아니라 직격이 가는 섬유를 포함한 굴곡진 표면에서는 stationary, advancing그리고 receding contact angle-을 신속하고 정확하게 측정할 수 있게 하여 준다. 가는 레이저광선이 액체와 고체사이 계면의 끝을 통과하여 tangent screen의 각도를 재는 눈금상에 중심으로부터 방사상으로 두개의 선이 나타나게 된다. 이때 눈금상에 투영된 두개의 레이저광선 사이의 각도를 접촉각으로 결정한다. 이 새로운 기구를 사용한 결과, PMMA(Perspex-CQ)상에서의 접촉각은 문헌상의 접촉각과 일치함으로써 간편하고 정확한 접촉각 측정법임을 입증할 수 있었다.