• Tribology and Lubricants
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• 제21권5호
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• pp.221-226
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• 2005

A new calibration method for exact measurement of friction force in atomic force microscope (AFM) is presented. A new conversion factor involves a contact factor affected by tip, cantilever and contact stiffness. Especially the effect of contact stiffness on the conversion factor between lateral force and lateral signal is considered. Conventional conversion factor and a new modified conversion factor were experimentally compared. Results showed that a new calibration method could minimize the effect of normal load on friction force and improve the conventional method. A new method could be applied to the specimens with different physical properties.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.247-250
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• 2000

This paper presents the dynamic analysis and experiment for a shaft system supported by angular contact ball bearings. Among others, the dynamic characteristics of bearings are significantly affected by axial preload and radial load applied. This paper rigorously analyzes the dynamic characteristics of a shaft system with angular contact ball bearings subject of axial preload so as to result in eigenvalues as well as bearing stiffness characteristics. Experiments are also performed to identify natural frequencies and stiffness characteristics of bearings implemented. Comparison is made on the theoretical and experimental results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.620-623
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• 2000

The leaf spring is generally used effectively in load supporting because it has tension-diffused function in comparison with other springs. Nowadays the leaf spring is used widely in the suspensions of automobile and trains. The stiffness and the damping characteristics of the leaf spring being essential for the performance of vehicles, the exact evaluation is required. Various approximate formula are normally used for the leaf spring design. however, accuracy and trust are decreased because the contact and frictional characteristics between leaf plates are generally neglected. In this paper, nonlinear stiffness matrix of the leaf spring is solved by contact-element applying FEM for considering the contact and frictional characteristics between leaf plates. The results of proposed FE model are compared with test data.

• 정보저장시스템학회논문집
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• 제8권1호
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• pp.33-38
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• 2012

To investigate of load/unload performance, FE (finite element) model of conventional suspension and HAMR suspension were made. The FE models were verified by modal analysis. In the loading simulation, the conventional system could stably load onto the disk without contact. On the other hand, the HAMR suspension which had an optical fiber and prism occurred slider - disk contact. In the unloading process, the conventional system was unloaded without contact. However, in the HAMR suspension, the contact between slider and disk was occurred at the moment that the dimple was separated during unload process. Therefore the load/unload performance of HAMR decrease with high stiffness, it is necessary that stiffness of HAMR suspension should reduced with design parameters of optical fiber and prism.

• 한국소음진동공학회논문집
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• 제12권8호
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• pp.639-647
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• 2002

The nonlinear vibration of the thin perforated plate is analyzed in consideration of the V-shaped tension distribution and the effect of wire impact damping. The reduced order FEM model of the tension plate is obtained from dynamic condensation for the mass and stiffness matrices. Tension wire is modeled using the lumped parameter method to effectively describe its contact interactions with the plate. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. From the evaluation of the computational accuracy and computation time for the deduced impact stiffness and damping coefficient, we determined proper values for the simulation works, accounting for the computational accuracy as well as the computational efficiency. Finally we discussed the results of nonlinear nitration analysis for variations of their design parameters.

• 비파괴검사학회지
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• 제28권3호
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• pp.292-301
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• 2008

A linearized model for hysteretic acoustic nonlinearity of imperfectly joined interface is proposed and analyzed by using Coulomb damping to investigate the characteristics of the reflection and transmission coefficients for harmonic waves at the contact interface. Closed crack is modeled as non welded interface that has nonlinear discontinuity condition in displacement across its boundary. Based on the hysteretic contact stiffness of the contact interface, the reflected and transmitted waves are determined by deriving the tractions on both sides of the interface in terms of the discontinuous displacements across the interface. It is found that the amplitudes of the reflected and transmitted waves are dependent on the frequency and the hysteretic stiffness. As the frequency of the incident wave increases, the higher reflection and lower transmission are obtained. It also shows that the hysteresis of the interface increases the reflection coefficient, but reduces the transmission coefficient. A fatigue crack is also made in aluminum specimen to demonstrate these characteristics of the reflection and transmission of contact interfaces.

• 한국지반공학회논문집
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• 제23권3호
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• pp.77-88
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• 2007

본 연구에서는 사질토의 탄성 및 탄소성 거동을 모사하기 위한 미시역학 기반의 구성 모델을 개발하였다. 개발 모델은 접촉 방향의 공간 분포를 통계적으로 처리한 조직 이방성, 응력비에 따른 조직 이방성의 변화, 간극비 변화에 따른 접촉점 수의 변화, 그리고 미시적 탄성-탄소성 접촉 강성을 고려하였다. 금속 재료에 대한 시험결과를 이용하여 미시적 탄소성 접촉 강성 모델을 수직 접촉력과 입자의 항복 접촉력에 대한 거듭제곱 함수의 형태로 유도하였다. 모델 변수를 정량적으로 평가하기 위해 직교 이방 탄성 계수의 근사식을 유도하였다.

• 대한기계학회논문집A
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• 제41권5호
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• pp.345-352
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• 2017

본 논문은 스퀼 시험을 통해 압력 변화에 의해 발생하는 스퀼 소음을 계측하고, 발생된 스퀼 소음을 FEM 복소수 고유치 해석으로 모드연성 불안정성을 구현하였다. FEM 해석에서 압력 변화에 따른 스퀼주파수 변화를 근사하기 위해서 접촉강성 변화에 의한 스퀼 민감도를 예측하고, 잠재적인 스퀼 모드를 유추하였다. 스퀼 실험 결과 1 kHz, 2.5 kHz, 3.5 kHz, 4 kHz 근방에서 스퀼 소음이 발생하였으며, 압력이 증가함에 따라 스퀼 주파수가 다소 증가되었다. FEM 해석 결과 접촉강성 변화에 따른 유사한 스퀼모드 및 민감도를 예측하였고, 해석시 접촉강성 변화가 스퀼실험에서의 압력증가 효과를 근사할 수 있음을 보였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.940-945
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• 2009

This paper presents the design method of low order controller for the active pantograph of electric train system. The pantograph is the most playa role to supply constant current to the train. The design objectives are to have good tracking performance about reference contact force despite the stiffness variation that is like sinusoidal function concerned in train speed or span length of contact wire. In this paper, we consider stiffness variation from external disturbance of active pantograph to simplify model equation, and propose simple second-order controller which is designed by Characteristic ratio assignment(CRA) control method. Finally, we verify time response appling to model equation of real system and frequency response about parameter uncertainty like stiffness variation. it is performed by Matlab version 6.5 and Matlab simulink simulation.

• Tribology and Lubricants
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• 제25권2호
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• pp.81-85
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• 2009

Interests in micro/nano-particles have been greatly increasing due to their wide applications in various fields such as environmental and medical sciences as well as engineering. In order to obtain a fundamental understanding of the tribological characteristics at particle-surface contact interface, frictional behaviors according to load/pressure and materials were obtained by using atomic force microscope(AFM) cantilevers with different stiffnesses and tips. Lateral contact stiffnesses were observed in various tip-surface contact situations. Experimental results show that stick-slip friction behavior occurs even when the colloidal probes with a particle of a few micrometers in diameter, which have a relatively large contact area and lack a well-shaped apex, were used. This indicates that atomic stick-slip friction may be a more common phenomenon than it is currently thought to be. Also, experimental results were investigated by considering the competition between the stiffness of the interatomic potential across the interface and the elastic stiffnesses of the contacting materials and the force sensor itself.