scholarly journals Long term friction: From stick-slip to stable sliding

2007 ◽  
Vol 34 (13) ◽  
pp. n/a-n/a ◽  
Author(s):  
Christophe Voisin ◽  
François Renard ◽  
Jean-Robert Grasso
Keyword(s):  
Stick Slip ◽  
Stable Sliding

Dynamic Behaviour of Plain Slideways

1966 ◽  
Vol 181 (1) ◽  
pp. 169-184 ◽  
Author(s):  
R. Bell ◽  
M. Burdekin
Keyword(s):  
Machine Tool ◽  
Dynamic Behaviour ◽  
Damping Capacity ◽  
Friction Characteristic ◽  
Stick Slip ◽  
Friction Characteristics ◽  
Physical Systems ◽  
Major Emphasis

The friction characteristics resulting from the motion of one surface over another form a very important facet of the behaviour of many physical systems. This statement is particularly valid when considering the behaviour of machine tool slideways. Most slideway elements consist of two plain surfaces whose friction characteristic is modified by the addition of a lubricant. In many cases the complete slideway consists of many mating surfaces and the choice of slideway material, slideway machining and lubricant is often influenced by the long term problem of wear. The aim of this paper is to present results of experiments on a test rig designed to be representative of machine tool slideway conditions; the experiments were wholly concerned with the behaviour of the bearing under dynamic conditions. The major emphasis is on results obtained with a polar additive lubricant which appears to exclude the possibility of ‘stick-slip’ oscillations. A parallel series of tests are reported where a normal hydraulic oil was used as lubricant. The use of this second lubricant allowed some study of the ‘stick-slip’ process. The dynamic friction characteristics, cyclic friction characteristics and damping capacity of several slideway surface combinations have been obtained and are discussed in the context of earlier work in the field and the role of slideways in machine tool behaviour.

Large-Scale Evaluation of Constrained Bearing Elements Made of Thermosetting Polyester Resin and Polyester Fabric Reinforcement

2006 ◽  
Vol 128 (4) ◽  
pp. 681-696 ◽  
Author(s):  
P. Samyn ◽  
W. Van Paepegem ◽  
J. S. Leendertz ◽  
A. Gerber ◽  
L. Van Schepdael ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Large Scale ◽  
Elastic Recovery ◽  
Small Scale ◽  
Practical Implementation ◽  
Fiber Failure ◽  
Stick Slip ◽  
Composite Surface ◽  
Pull Out ◽  
Stable Sliding

Polymer composites are increasingly used as sliding materials for high-loaded bearings, however, their tribological characteristics are most commonly determined from small-scale laboratory tests. The static strength and dynamic coefficients of friction for polyester/polyester composite elements are presently studied on large-scale test equipment for determination of its bearing capacity and failure mechanisms under overload conditions. Original test samples have a diameter of 250 mm and thickness of 40 mm, corresponding to the practical implementation in the sliding surfaces of a ball-joint, and are tested at various scales for simulation of edge effects and repeatability of test results. Static tests reveal complete elastic recovery after loading to 120 MPa, plastic deformation after loading at 150 MPa and overload at 200 MPa. This makes present composite favorable for use under high loads, compared to, e.g., glass-fibre reinforced materials. Sliding tests indicate stick-slip for pure bulk composites and more stable sliding when PTFE lubricants are added. Dynamic overload occurs above 120 MPa due to an expansion of the nonconstrained top surface. A molybdenum-disulphide coating on the steel counterface is an effective lubricant for lower dynamic friction, as it favorably impregnates the composite sliding surface, while it is not effective at high loads as the coating is removed after sliding and high initial static friction is observed. Also a zinc phosphate thermoplastic coating cannot be applied to the counterface as it adheres strongly to the composite surface with consequently high initial friction and coating wear. Most stable sliding is observed against steel counterfaces, with progressive formation of a lubricating transfer film at higher loads due to exposure of PTFE lubricant. Composite wear mechanisms are mainly governed by thermal degradation of the thermosetting matrix (max. 162°C) with shear and particle detachment by the brittle nature of polyester rather than plastic deformation. The formation of a sliding film protects against fiber failure up to 150 MPa, while overload results in interlaminar shear, debonding, and ductile fiber pull-out.

Low friction states for thin solid lubricant film of MoS2

2018 ◽  
Vol 70 (4) ◽  
pp. 639-644 ◽  
Author(s):  
Kwang-Hua R. Chu
Keyword(s):  
Thin Films ◽  
Solid Lubricant ◽  
Activation Volume ◽  
High Vacuum ◽  
Low Friction ◽  
Friction Behavior ◽  
Stick Slip ◽  
Content Type ◽  
Term Operation

Purpose During the operation of Wendelstein 7-X (W7-X), any mechanical disturbance such as stick-slip may cause quenching of superconducting (SC) coils. The friction behavior of MoS2 lubrication (thin film) for narrow support elements between the SC coils in W7-X is rather important, as there is a design requirement for a coefficient of friction (COF) 0.05 between the sliding surfaces to control the stress contribution (from friction). Design/methodology/approach The author has carried out intensive calibrations or verifications using verified models considering previous friction tests on various samples which measured the COF in 4.2 K, 77 K and room temperature conditions (at high vacuum) to simulate the actual working condition. Findings The author has given useful explanations and diagnosis for previous anomalous scattered data. To improve the performance of MoS2, the author has predicted its better COF (0.002 via tuning of the activation volume), which could be a superlubricating state for MoS2 thin films considering the long-term operation requirement W7-X. Originality/value In this paper, the author has adopted Eyring’s approach to predict the low COF (0.002 via tuning of the activation volume), which could be a superlubricating state for MoS2 thin films considering the long-term operation requirement W7-X. Finally, some recent progresses about the possible few-layer MoS2 role in the electromagnetic loads have been provided.

Rubber Viscoelasticity Using the Physically Constrained System's Stretches as Internal Variables

1993 ◽  
Vol 66 (4) ◽  
pp. 567-577 ◽  
Author(s):  
Arthur R. Johnson ◽  
Ross G. Stacer
Keyword(s):  
Energy Function ◽  
Large Strain ◽  
Strain Relaxation ◽  
Time Dependent ◽  
Internal Variables ◽  
Relaxation Equation ◽  
Stick Slip ◽  
History Of ◽  
Term Energy

Abstract The simulation of rubber viscoelasticity with the tube reptation model for topological interactions is investigated for large dynamic strains. The chemically crosslinked (CC) system of molecules acts as a constraint box per unit volume for the physically constrained (PC) system and carries the PC system during the deformation process. A stick—slip model is used to simulate the interaction between the CC and PC systems Stretch ratios describe the history of the PC system's energy. Rubber energy density functions for both the CC and time dependent PC systems are shown to model large strain viscoelastic deformations. In this approach the energy is split into two terms. The long term energy function for the CC molecules represents one part and a time dependent energy function for the PC molecules comprises the second part. The PC systems' stretches then appear as internal variables in the expression of the total energy. The relaxation of the PC molecules during a general deformation is determined by the history of the CC system's strain state and the box (tube) stick—slip relaxation equation(s). Examples are presented in which step-strain relaxation test data and strain rate data are simulated for large deformations of a rubber compound with differing short and long term energy functions.

scholarly journals Tidal pacing, skipped slips and the slowdown of Whillans Ice Stream, Antarctica

2014 ◽  
Vol 60 (222) ◽  
pp. 795-807 ◽  
Author(s):  
J. Paul Winberry ◽  
Sridhar Anandakrishnan ◽  
Richard B. Alley ◽  
Douglas A. Wiens ◽  
Martin J. Pratt
Keyword(s):  
Elastic Strain ◽  
Temporal Evolution ◽  
Flow Speed ◽  
Stick Slip ◽  
Ice Stream ◽  
Steady Rate ◽  
Decadal Scale ◽  
Whillans Ice Stream ◽  
Stick Slip Motion

AbstractWe summarize new observations of the deceleration and stick–slip motion of Whillans Ice Stream (WIS), Antarctica. We refine the location of the large sticky spots that resist motion between slip events, the locations of which are controlled by the patterns of subglacial water flow. Our examination of the long-term velocity time series for the ice stream reveals that the decadal-scale deceleration is not occurring at a steady rate, but varies at the sub-decadal timescale. This unsteady deceleration modulates the temporal evolution of a broad (~50 km across) surface-elevation bulge forming at the junction between the relatively narrow upstream portion of the ice stream and broad ice plain that constitutes the downstream end of WIS. Comparison of observations from April 2003 and November 2010 reveals significant changes in the tidally modulated stick–slip cycle that regulates motion on the ice plain. We observe that the timing of slip events has become less regular in response to decreased flow speed in the upstream portions of the ice stream. The decreased regularity of slip events has reduced the release of stored elastic strain during slip events, increasing the rate of deceleration.

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