• 한국정밀공학회지
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• 제13권11호
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• pp.92-99
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• 1996

The contact pressure in jointed plates was measured by means of an improved ultrasonic technique. In order to get calibration curve, the relationship between contact pressure and ratio of boundary and bottom echo of normal beam probes were obtained for the calibration blocks with various surface roughness. The ratio of boundary and bottom echoes were measured for the upper/under plates locally compressed with uniform pressure, and the distribution of contact pressure was obtaines. The measured pressure has a good agreement with results of FEM analysis. Thus the proposed ultrasonic method in this work is very useful to measure the contact pressure.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.310-315
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• 2001

The most general feature of contact zone among the mechanical components is elliptical circle. In particular, continuously variable transmission (CVT) of toroidal type has elliptical shape of contact zone under the elastohydrodynamic lubrication condition, where the power is transmitted by the shearing the efluid. Due to the traction of the shear behaviors of lubricant over the small elliptical contact zone, high power of torque is transmitted. During the power transmission, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spinning. The spinning effect that is not common contact behavior in tribological components frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of elastohydrodynamic lubrication with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.

• Tribology and Lubricants
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• 제21권3호
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• pp.136-141
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• 2005

Analytical model to calculate the contact fatigue life of rough surface is presented in this paper. The effect of surface roughness can be calculated by this model. Computational method and the theoretical basis are also discussed. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. As a result of analysis the relationship between the life and the roughness as well as the most probable depth of the crack initiation is calculated.

• Tribology and Lubricants
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• 제23권6호
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• pp.272-277
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• 2007

Various type of rotary unions are widely used to provide fluids between rotating parts. To prevent fluid leakage, most of the rotary unions adopt mechanical seals which is highly reliable but too expensive and complicate. In this paper, a simple lip seal system made of PTFE is adopted in designing of a compact rotary union. Using MARC, the behavior characteristics of lip seal are investigated for seal mounting process, and obtained variations of contact pressure distribution and contact width with interferences and fluid pressures. The results showed that contact width are increased with interference and pressure. The maximum contact pressure are also increased up to a certain interference and pressure, however, then decreased. The numerical methods and results can be applied in designing and performance improvement of lip seal adopted rotary union, and further extensive studies are required.

• 한국초전도ㆍ저온공학회논문지
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• 제17권4호
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• pp.1-7
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• 2015

This paper addresses technical problems of thermal contact conductance or resistance which inevitably occurs in most cryogenic engineering systems. The main focus of this paper is to examine what kind of physical factors primarily influences the thermal contact resistance and to suggest how it can be minimized. It is a good practical rule that the contact surface must have sub-micron roughness level with no oxide layer and be thinly covered by indium, gold, or Apiezon-N grease for securing sufficient direct contact area. The higher contact pressure, the lower the thermal contact resistance. The general description of this technique has been widely perceived and reasonable engineering results have been achieved in most applications. However, the detailed view of employing these techniques and their relative efficacies to reduce thermal contact resistances need to be thoroughly reviewed. We should consider specific thermal contact conditions, examine the engineering requirements, and execute each method with precautions to fulfil their maximum potentials.

• 대한기계학회논문집
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• 제17권7호
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• pp.1658-1667
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• 1993

In this research, a numerical algorithm has been developed, which can be applied to the large deformation and large displacement contact problems between two deformable bodies. The contact conditions expressed in terms of the rate of angle change have been proposed considering the change in geometric shape and rate of contact force. A set of linear simultaneous equations is constructed by adding the geometric shape change and contact conditions to the original stiffness matrix. A new method to determine time increment has been proposed based on Euler method, in which the condition to prevent the contact bodies from penetrating and overrunning each other has been taken into consideration. Practical application to contact problem is extrusion in which bodies are sliding along the contact boundary.

• 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.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1269-1279
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• 2023

Pool boiling experiments are performed within an isolated bubble regime at inclination angles of 0° and 45°. When a bubble grows and departs from the heating surface, the pressure, buoyancy, and surface tension force play important roles. The curvature and base diameter are required to calculate the pressure force, the bubble volume is required to calculate the buoyancy force, and the contact angle and base diameter are required to calculate the surface tension force. The contact angle, base diameter, and volume of the bubbles are evaluated using images captured via a high-speed camera. The surface tension force equation proposed by Fritz is modified with the contact angles obtained in this study. When the bubble grows, the contact angle decreases slowly. However, when the bubble departs, the contact angle rapidly increases owing to necking. At an inclination angle of 0°, the contact angle is calculated as 82.88° at departure. Additionally, the advancing and receding contact angles are calculated as 70.25° and 82.28° at departure, respectively, at an inclination angle of 45°. The dynamic behaviors of bubble growth and departure are discussed with forces by pressure, buoyancy, and surface tension.

• Journal of Mechanical Science and Technology
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• 제16권8호
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• pp.1117-1126
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• 2002

A conducting crack in an electrostrictive ceramic under combined electric and mechanical loading is investigated. Analysis based on linear dielectric model predicts that the surfaces of the crack are not open completely but they are contact near the crack tip. The complete solution for the crack with a contact zone in a linear electrostrictive ceramic under combined electric and mechanical loading is obtained by using the complex variable formula. The asymptotic problems for a semi-infinite crack with a partial opening zone as well as for a fully open semi-infinite crack in a nonlinear electrostrictive ceramic are analyzed in order to investigate the effect of the electrical nonlinearity on the stress intensity factor under small scale nonlinear conditions. Particular attention is devoted to a finite crack in the nonlinear electrostrictive ceramic subjected to combined electric and mechanical loading. The stress intensity factor for the finite crack under small scale nonlinear conditions is obtained from the asymptotic analysis.

• Tribology and Lubricants
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• 제25권5호
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• pp.335-341
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• 2009

Elastohydrodynamic lubrication (EHL) analysis shows that film thickness is very flat in the contact area and pressure distribution is somehow similar to that of Hertzian contact pressure except the outlet region with pressure spike. These typical patterns of EHL film thickness and pressure are the cases under the steady contact conditions of applied loads and speeds. However, many engineering contacts are rather under the conditions of varying loads and contact speeds, and therefore the predictions for endurance life and performance of machine elements with steady EHL analysis are not suitable in many occasions. This study shows the differences in film thickness formation and pressure distribution between steady and transient contact conditions in several contact cases.