On the question of whether lubricants fluidize in stick–slip friction

Intermittent sliding (stick–slip motion) between solids is commonplace (e.g., squeaking hinges), even in the presence of lubricants, and is believed to occur by shear-induced fluidization of the lubricant film (slip), followed by its resolidification (stick). Using a surface force balance, we measure how the thickness of molecularly thin, model lubricant films (octamethylcyclotetrasiloxane) varies in stick–slip sliding between atomically smooth surfaces during the fleeting (ca. 20 ms) individual slip events. Shear fluidization of a film of five to six molecular layers during an individual slip event should result in film dilation of 0.4–0.5 nm, but our results show that, within our resolution of ca. 0.1 nm, slip of the surfaces is not correlated with any dilation of the intersurface gap. This reveals that, unlike what is commonly supposed, slip does not occur by such shear melting, and indicates that other mechanisms, such as intralayer slip within the lubricant film, or at its interface with the confining surfaces, may be the dominant dissipation modes.

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Squeezing and stick–slip friction behaviors of lubricants in boundary lubrication

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1805569115 ◽

2018 ◽

Vol 115 (26) ◽

pp. 6560-6565 ◽

Cited By ~ 15

Author(s):

Rong-Guang Xu ◽

Yongsheng Leng

Keyword(s):

Phase Transition ◽

Boundary Lubrication ◽

Sliding Friction ◽

Surface Force ◽

Lubricant Film ◽

Force Balance ◽

Surface Boundary ◽

Stick Slip ◽

Squeeze Out ◽

Dynamics Simulations

The fundamental questions of how lubricant molecules organize into a layered structure under nanometers confinement and what is the interplay between layering and friction are still not well answered in the field of nanotribology. While the phase transition of lubricants during a squeeze-out process under compression is a long-standing controversial debate (i.e., liquid-like to solid-like phase transition versus amorphous glass-like transition), recent different interpretations to the stick–slip friction of lubricants in boundary lubrication present new challenges in this field. We carry out molecular dynamics simulations of a model lubricant film (cyclohexane) confined between molecularly smooth surfaces (mica)––a prototypical model system studied in surface force apparatus or surface force balance experiments. Through fully atomistic simulations, we find that repulsive force between two solid surfaces starts at about seven lubricant layers (n= 7) and the lubricant film undergoes a sudden liquid-like to solid-like phase transition atn< 6 monolayers thickness. Shear of solidified lubricant films at three- or four-monolayer thickness results in stick–slip friction. The sliding friction simulation shows that instead of shear melting of the film during the slip of the surface, boundary slips at solid–lubricant interfaces happen, while the solidified structure of the lubricant film is well maintained during repeated stick–slip friction cycles. Moreover, no dilation of the lubricant film during the slip is observed, which is surprisingly consistent with recent surface force balance experimental measurements.

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Dynamics of stick–slip motion, Whillans Ice Stream, Antarctica

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2011.02.052 ◽

2011 ◽

Vol 305 (3-4) ◽

pp. 283-289 ◽

Cited By ~ 41

Author(s):

J. Paul Winberry ◽

Sridhar Anandakrishnan ◽

Douglas A. Wiens ◽

Richard B. Alley ◽

Knut Christianson

Keyword(s):

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Stick Slip Motion ◽

Slip Motion

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On the Dynamic Behavior of Machine Tool Slideway : 2nd Report, Characteristics of Kinetic Friction in "Stick Slip" Motion

Bulletin of JSME ◽

10.1299/jsme1958.13.180 ◽

1970 ◽

Vol 13 (55) ◽

pp. 180-188 ◽

Cited By ~ 2

Author(s):

Shinobu KATO ◽

Katsumi YAMAGUCHI ◽

Tsuneo MATSUMAYASHI

Keyword(s):

Machine Tool ◽

Dynamic Behavior ◽

Kinetic Friction ◽

Stick Slip ◽

Stick Slip Motion ◽

Slip Motion

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Dynamic simulation of stick–slip motion of a flexible solar array

Control Engineering Practice ◽

10.1016/j.conengprac.2006.11.014 ◽

2008 ◽

Vol 16 (6) ◽

pp. 724-735 ◽

Cited By ~ 19

Author(s):

Yasushi Kojima ◽

Shigemune Taniwaki ◽

Yoshiaki Okami

Keyword(s):

Dynamic Simulation ◽

Solar Array ◽

Stick Slip ◽

Stick Slip Motion ◽

Slip Motion

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Basal ice motion and deformation at the ice-sheet margin, West Greenland

Annals of Glaciology ◽

10.3189/172756405781813113 ◽

2005 ◽

Vol 42 ◽

pp. 67-70 ◽

Cited By ~ 5

Author(s):

David M. Chandler ◽

Richard I. Waller ◽

William G. Adam

Keyword(s):

Deformation Mode ◽

Time Intervals ◽

Stick Slip ◽

Active Deformation ◽

West Greenland ◽

Shear Structures ◽

Basal Ice ◽

Ice Velocity ◽

Stick Slip Motion ◽

Slip Motion

AbstractMeasurements of basal ice deformation at the margin of Russell Glacier, West Greenland, have provided an opportunity to gain more insight into basal processes occurring near the margin. The basal ice layer comprises a debris-rich, heterogeneous stratified facies, overlain by a comparatively debris-poor dispersed facies. Ice velocities were obtained from anchors placed in both ice facies, at three sites under 5–15 m ice depth. Mean velocities ranged from 20 to 43 m a–1, and velocity gradients indicate high shear strain rates within the basal ice. Stick–slip motion and diurnal variations were observed during measurements at short (1–5 min) time intervals. Vertical gradients in horizontal ice velocity indicate two modes of deformation: (1) viscous deformation within the stratified ice facies, and (2) shear at the interface between the two basal ice facies. Deformation mode 1 may contribute to the folding and shear structures observed in the stratified facies. Deformation mode 2 may generate the stick–slip motion and be associated with the formation of debris bands. Active deformation close to the margin suggests that structures observed within the basal ice are only partially representative of processes occurring near the bed in areas away from the glacier margin.

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Monitoring Stick-Slip Motion of Machine Tool Slides using Feed Motor Current

10.1109/imc.1990.687390 ◽

2005 ◽

Author(s):

J.L. Stein ◽

Wei Wu

Keyword(s):

Machine Tool ◽

Stick Slip ◽

Motor Current ◽

Stick Slip Motion ◽

Slip Motion

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Experimental Exploration of Schallamach Waves and Self-Excitation in a Belt-Drive System

Volume 6: 14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control ◽

10.1115/detc2018-85894 ◽

2018 ◽

Author(s):

Yingdan Wu ◽

Michael Varenberg ◽

Michael J. Leamy

Keyword(s):

Angular Velocity ◽

Dynamic Behavior ◽

Oscillation Amplitude ◽

Operating Conditions ◽

Drive System ◽

Belt Drive ◽

Stick Slip ◽

Stick Slip Motion ◽

System Inertia ◽

Slip Motion

We study the dynamic behavior of a belt-drive system to explore the effect of operating conditions and system moment of inertia on the generation of waves of detachment (i.e., Schallamach waves) at the belt-pulley interface. A self-excitation phenomenon is reported in which frictional fluctuations serve as harmonic forcing of the pulley, leading to angular velocity oscillations which grow in time. This behavior depends strongly on operating conditions (torque transmitted and pulley speed) and system inertia, and differs between the driver and driven pulleys. A larger net torque applied to the pulley generally yields more remarkable stick-slip oscillations with higher amplitude and lower frequency. Higher driving speeds accelerate the occurrence of stick-slip motion, but have little influence on the oscillation amplitude. Contrary to our expectations, the introduction of flywheels to increase system inertia amplified the frictional disturbances, and hence the pulley oscillations. This does, however, suggest a way of facilitating their study, which may be useful in follow-on research.

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