• Tribology and Lubricants
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• 제11권5호
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• pp.1-9
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• 1995

The mechanism of various spherical particles formation from wide range of tribo-systerns is suggested and deduced by the action of micro-explosion on the basis of the thermally-activated wear theory, in which the flash temperature at contact could be reached clearly upto the material molten temperature due to the secondary activation energy from the exothermic reactions involving lubricant thermo-decomposition, metals oxidation, hydrogen reactions and other possible complex thermo-reactions at the contacts. Various shapes of spherical particles generated from the tribosystem can be explained by the toroidal action of micro-explosion accompanied with the complex thermo-chemical reactions at the contact surfaces or sub-surfaces.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.469-483
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• 2014

In an indentation approach, the smooth rigid spherical ball penetrated into a deformable flat is considered for the study based on contact mechanics approach. The elastic-plastic frictionless spherical indentation analysis has been under taken in the finite element analysis using "ABAQUS" and experimental study. The spherical indentation has been studied for the materials like steel, aluminium, copper and brass with an identical spherical indenter for diverse indentation depths. The springback analysis is executed for studying the actual indentation depth after the indenter is unloaded. In the springback simulation, the material recovers its elastic deformation after the indenter is unloaded. The residual diameter and depth of an indentation for various materials are measured and compared with simulation results. It shows a good agreement between the simulation and an experimental studies.

• 한국안광학회지
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• 제14권1호
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• pp.39-45
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• 2009

목적: 본 연구는 약도의 근시성 난시안의 토릭 소프트 렌즈와 다른 교정 방법의 효과를 알아보기 위해 대비감도 검사와 눈부심 장애 검사를 이용하여 시력의 질을 비교하였다. 방법: 1.50D이하의 경도 난시의 근시안인 남녀 대학생 20명(40안)을 대상으로 5가지 다른 방법(소프트렌즈 등가구면, 토릭 소프트 렌즈, RGP 렌즈, 난시교정 안경, 안경 등가구면)으로 교정하였다. 모든 대상자는 교정시력이 20/20(1.0) 이상이었다. 대비감도 검사와 눈부심 장애 검사는 OPTEC$^{(R)}$ 6500을 이용하여 밝은 조도과 어두운(글레어) 조도에서 실시하였다. 결과: 밝은 조도 하에서 난시교정 안경이 모든 공간주파수에서 가장 높은 대비감도를 나타내었고, 토릭 소프트 렌즈, RGP 렌즈, 안경 등가구면, 소프트 콘택트렌즈 등가구면 처방 순으로 대비감도가 낮아지는 것으로 나타났다. 그러나 모두 정상 범위의 대비감도 영역에 포함되었다. 어두운 조도(글레어) 하에서는 토릭 소프트 렌즈 착용자가 가장 높은 대비감도를 나타내었고, RGP렌즈, 안경 등가구면, 난시교정 안경, 소프트 렌즈 등가구면 처방 순으로 대비감도가 낮아지는 것으로 나타났다. 구면 소프트렌즈 착용자는 어두운 조도(글레어) 하에서 정상 영역보다 낮은 대비감도 값을 보였다. 결론: 약도의 근시성 난시안의 교정으로 토릭 소프트 렌즈 교정이 구면 소프트렌즈보다 좋은 시력의 질(대비감도)을 보인 것으로 나타났다. 어두운 조명에서 콘택트렌즈를 착용해야할 경우에는 토릭 소프트렌즈가 우수한 것으로 사료된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.297-301
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• 2004

The optimum design against contact crack initiation is investigated to find major parameters in designing desirable surface-coated asymmetric layered components. Hard ceramic coated soft materials with various elastic modulus mismatch are prepared for the analysis. Spherical indentation is conducted for producing contact cracks from the surface or interface between the coating and the substrate layer. A finite element analysis of the stress fields in the loaded layer components enables a direct correlation between the damage patterns and the stress distributions. Implications concerning the design of asymmetric layered components indicate that the coating thickness and the elastic modulus mismatch are important parameters for designing layered component to prevent the initiation of contact cracks.

• Journal of Advanced Marine Engineering and Technology
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• 제30권8호
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• pp.863-869
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• 2006

A new CVT, the inner spherical traction CVT (ISCVT) is introduced. Transmission of the most scooters is the self-controlled variable pulley-belt type of CVT having some disadvantages in the fuel consumption and the limitation of the transmittable power due to the slippage between the belt and pulley. Unlike this, ISCVT controlled directly by driver is more efficient and the contact mechanism having the same line of contact normal of the spherical rotors of different radii on common center causes that the power density and torque capacity are remarkably improved. The prototype with the specifications of 50cc scooter is designed and tested.

• 한국정밀공학회지
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• 제12권5호
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• pp.46-56
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• 1995

As demands on the precision bevel gears are increased in the related industry, the exact kinematical investigations of a pair of spherical involute bevel gears are required for the computer aided design. The exact angular velocity ratio based on the characteristics of the spherical involute tooth is derived and verified from the relationship between rotational angles. Elementary kinematics of the gearsets is investigated by applying the transformation of the coordinate systems. The tooth contact lines based on logarithmic tooth-wise curve are examines in three dimentional space. Contact ratio is formulated and simulated according to the system parameters such as shaft angles, pressure angle, and spiral angles. The condition of teeth interference is dervied and the critical numbers of gear teeth are calculated. The whole surface geometry of a spiral bevel gearsets are discretized and visualized by a computer graphic tool.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2008년도 추계학술대회 논문집
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• pp.567-568
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• 2008

• 한국안광학회지
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• 제14권1호
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• pp.31-38
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• 2009

목적: 본 연구는 구면 렌즈에 비해 후면 비구면 RGP(Rigid Gas Permeable) 렌즈의 각막 지형도 변화, 시력의 질 그리고 임상 증상을 평가하고자 시행하였다. 방법: 전체 37명을 대상으로 우안에는 구면 RGP 렌즈, 좌안에는 후면 비구면 RGP 렌즈를 피팅하여 2개월 동안 착용 후 각막지형도와 대비감도의 변화를 평가하였다. 결과: 37명의 대상자 중 34명이 성공적으로 2개월 동안 렌즈를 착용하였다. 각막 지형도는 구면과 비구면 RGP 렌즈 사이에 차이를 보이지 않았다. 비구면 렌즈를 착용한 눈이 구면 렌즈를 착용한 눈과 비교해서 밝은 조도에서 대비감도가 현저하게 감소된 것으로 나타났다. 착용감과 눈 건강에서도 구면 렌즈를 선호하는 대상자가 많았다. 결론: RGP 렌즈의 구면과 후면 비구면 렌즈를 비교한 결과, 각막지형도에는 대상자간에 유의한 차이가 없었다. 밝은 조도에서 시력의 질과 선호도는 구면 RGP 렌즈가 비구면 RGP 렌즈 보다 우수한 것으로 나타났다. 콘택트렌즈 디자인에 의해 유발되는 수차에 대한 더 많은 연구가 시력의 질에 대한 차이를 설명해 줄 수 있을 것으로 사료된다.

• Tribology and Lubricants
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• 제28권1호
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• pp.1-6
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• 2012

In this paper, a three elastic body sliding contact problem is modeled to investigate more precise wear mechanisms related with the sealing surface. A 3-D finite element contact model, a small spherical elastic particle, PTFE seal and steel surface, is solved using a nonlinear finite element code MARC. The deformed seal and steel surface shapes, von-Mises and principal stress distributions are obtained for different seal sliding distances. The entrapped small particle within PTFE seal results in very high stresses on the steel surface which exceeded its yield strength and produce plastic deformation such as groove and torus. The sealing surface could also be worn down by sub-surface fatigue due to intervening small particles together with the well-known abrasive wear. Therefore the proposed contact model adopted in this paper can be applied in design of various sealing systems, and further studies are required.

• Interaction and multiscale mechanics
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• 제1권4호
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• pp.411-422
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• 2008

Atomistic simulation of nanoindentation with spherical indenters was carried out to study dislocation structures, mean contact pressure, and nanohardness of Au and Al thin films. Slip vectors and atomic stresses were used to characterize the dislocation processes. Two different characteristics were found in the induced dislocation structures: wide-spread slip activities in Al, and confined and intact structures in Au. For both samples, the mean contact pressure varied significantly during the early stages of indentation but reached a steady value soon after the first apparent load drop. This indicates that the nanohardness of Al and Au is not affected by the indentation depth for spherical indenters, even at the atomistic scale.