• Tribology and Lubricants
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• v.28 no.6
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• pp.289-296
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• 2012

Atomic force microscopy (AFM) has been used for imaging surfaces and measuring surface forces at the nano-scale. Force calibration is important for the quantitative measurement of forces at the nano-scale using AFM. Normal force calibration is relatively straightforward, whereas the lateral force calibration is more complicated since the lateral stiffness of the cantilever is often comparable to the contact stiffness. In this work, the lateral force calibrations of the rectangular cantilever were performed using torsional Sader's method, thermal noise method, and wedge calibration method. The lateral optical lever sensitivity for the thermal noise method was determined from the friction loop under various normal forces as well. Experimental results showed that the discrepancies among the results of the different methods were as large as 30% due to the effect of the contact stiffness on the lateral force calibration of the cantilever used in this work. After correction for the effect of contact stiffness, all the calibration results agreed with each other, within experimental uncertainties.

• Tribology and Lubricants
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• v.21 no.5
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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.

• Tribology and Lubricants
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• v.23 no.1
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• pp.9-13
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• 2007

Despite numerous researches on atomic-scale friction have been carried out for understanding the origin of friction, lots of questions about sliding friction still remain. It is known that friction at atomic-scale always shows unique phenomena called 'stick-slips' which reflect atomic lattice of a scanned surface. In this work, experimental study on the effects of system stiffnesses and load on the atomic-scale stick-slip friction of graphite was performed by using an Atomic Force Microscope and various cantilevers/tips. The objective of this research is to figure out the dependency of atomic-scale friction on the nanomechanical properties in sliding contact such as load, stiffness and contact materials systematically. From this work, the experimental observation of transitions in atomic-scale friction from smooth sliding to multiple stick-slips in air was first made, according to the lateral cantilever stiffness and applied normal load. The superlubricity of graphite could be verified from friction vs. load experiments. Based on the results, the relationship between the stickslip behaviors and contact stiffness was carefully discussed in this work. The results or this work indicate that the atomic-scale stick-slip behaviors can be controlled by adjusting the system stiffnesses and contact materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1937-1941
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• 2004

We present lateral actuated piezoelectric actuator using U-shaped PZT strip and lever structure for the RF switch application. In the previous study of RF switch, they used horizontal contact switch fabricated by thin film metals. However, thin film metals could not generate large contact force due to low stiffness. In this work, we suggest lateral contact switch which makes large contact force by increasing stiffness. In addition, we use PZT actuator for the high force actuation. Generally actuator using thin film PZT moves to the vertical direction due to the neutral axis shift. Therefore we need lateral motion generation mechanism based on the thin film PZT actuator. In order to increase lateral motion of thin film PZT actuator, we use U-shaped PZT actuator using residual stress control. Also, thin film PZT actuator can generate very small lateral motion of 120${\times}$10$^{-6}$ ${\mu}{\textrm}{m}$/V for d$_{31}$ mode, thus we suggest lever structure to increase stroke amplification. From the experimental study, fabricated PZT actuator shows maximum lateral displacement of 1 ${\mu}{\textrm}{m}$, and break down voltage of the thin film PZT actuator is above 16V.

• Tribology and Lubricants
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• v.29 no.3
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• pp.160-166
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• 2013

There is an indispensable need for force calibration for quantitative nanoscale force measurement using atomic force microscopy. Calibrating the normal force is relatively straightforward, whereas doing so for the lateral force is often complicated because of the difficulty in determining the optical lever sensitivity. In particular, the lateral force calibration of a colloidal probe in a liquid environment often has a larger uncertainty as a result of the effects of the epoxy, the location of the colloidal particle on the cantilever, and a decrease in the quality factor. In this work, the lateral force of a colloidal probe using a reference cantilever with a known spring constant was calibrated in a liquid environment. By obtaining the spring constant and the lateral sensitivity at the equator of a spherical colloidal particle, the damage to the bottom surface of the colloidal particle could be eliminated. Further, it was shown that the effect of the contact stiffness on the determination of the lateral spring constant of the cantilever could be minimized. It was concluded that this method can be effectively used for the lateral force calibration of a colloidal probe in a liquid environment.

• Tribology and Lubricants
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• v.28 no.5
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• pp.203-211
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• 2012

Atomic force microscopy (AFM) has been used as a tool, not only for imaging surfaces, but also for measuring surface forces and mechanical properties at the nano-scale. Force calibration is crucial for quantitatively measuring the forces that act between the AFM probe of a force sensing cantilever and a sample. In this work, the lateral force calibrations of a V-shaped cantilever were performed using the finite element method, multiple pivot loading, and thermal noise methods. As a result, it was shown that the multiple pivot loading method was appropriate for the lateral force calibration of a V-shaped cantilever. Further, through crosschecking of the abovementioned methods, it was concluded that the thermal noise method could be used for determining the lateral spring constants as long as the lateral deflection sensitivity was accurately determined. To obtain the lateral deflection sensitivity from the sticking portion of the friction loop, the contact stiffness should be taken into account.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.60-67
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• 2000

As the speed of rotating machines increases and also their weight decreases, the coupling between lateral and torsional vibrations must be considered. In the past, rotordynamics and geardynamics have tended to treat the lateral and torsional vibrations of the system elements as separate and decoupled mechanisms. In the paper, the coupled lateral-torsional free and forced vibration of rotors trained by gears is analyzed using finite element method. Also the complicated variation of the meshing stiffness as a function of contact point along the line of action is estimated correctly. The gear mesh model is assumed to be linear with constant average mesh stiffness.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.417-422
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• 2004

The vibration of a running vehicle can be classified on lateral, longitudinal and vertical motions. The important factor on the stability and ride quality of a railway vehicle is the lateral motion. The contact between wheel and rail with conicity influences strongly on the lateral motion. In this study, an experiment for the vibration of a running railway vehicle was performed using a small scale railway vehicle model. Also, the effects on the car body, bogie and wheelset were examined for the weight and the stiffness of the first and second suspension. The experimental results showed that the lateral vibration increases as the wheel conicity and stiffness of the second suspension increase. And the lateral vibration of the bogie increases as the mass ratio between car body and bogie increases. Also, the lateral vibration of the wheel becomes high at low speed, while the wheel of 1/20 conicity makes severe vibration at high speed running.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.104-112
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• 2006

The influence of tire belt angle on the Plysteer Residual Aligning Torque(PRAT) and the cornering stiffness by the FEM has been studied. The PRAT is a performance factor of the tire about vehicle pull, and the cornering stiffness has relation to vehicle steering response of outdoor test. To validate FE model for analysis, simulation data for both the static stiffness(vertical, lateral) and the PRAT have been compared with the experimental data. In addition to the characteristics of the PRAT and the cornering stiffness due to the tire belt angle, rolling and cornering contact characteristics have been studied. The tendency of the PRAT and the cornering stiffness due to the belt angle can be used as a guide line for the tire design in relation to vehicle pull and vehicle steering response.

• Tribology and Lubricants
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• v.25 no.2
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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.