Running with Scissors: Cut-Ups, Boundary Friction and Creative Reuse

2014 ◽  
pp. 3-16 ◽  
Author(s):  
Tony Veale
Keyword(s):  
Boundary Friction

Effect of boundary friction on revere fault rupture propagation in centrifuge tests

2021 ◽  
Vol 147 ◽  
pp. 106811
Author(s):  
Chaofan Yao ◽  
Jiro Takemura ◽  
Gaoyu Ma ◽  
Cong Dai ◽  
Zheli An
Keyword(s):  
Boundary Friction ◽  
Rupture Propagation ◽  
Fault Rupture ◽  
Centrifuge Tests ◽  
Fault Rupture Propagation

scholarly journals Structure and peculiarities of boundary friction of ta-C coatings obtained by pulse-plasma deposition

2021 ◽  
Vol 1799 (1) ◽  
pp. 012027
Author(s):  
V D Samusenko ◽  
I A Zavidovskii ◽  
O A Streletskii ◽  
I A Buyanovskii ◽  
M M Khrushchov ◽  
...  
Keyword(s):  
Plasma Deposition ◽  
Boundary Friction ◽  
Pulse Plasma

scholarly journals Boundary Friction of ZDDP Tribofilms

2020 ◽  
Vol 69 (1) ◽  
Author(s):  
Jie Zhang ◽  
Mao Ueda ◽  
Sophie Campen ◽  
Hugh Spikes
Keyword(s):  
Friction Coefficient ◽  
Group Structure ◽  
Boundary Friction ◽  
Considerable Proportion ◽  
Base Oil ◽  
Characteristic Boundary ◽  
Long Duration ◽  
Structure Boundary ◽  
Alkoxy Groups ◽  
20 Nm

AbstractThe frictional properties of ZDDP tribofilms at low entrainment speeds in boundary lubrication conditions have been studied in both rolling/sliding and pure sliding contacts. It has been found that the boundary friction coefficients of these tribofilms depend on the alkyl structure of the ZDDPs. For primary ZDDPs, those with linear alkyl chains give lower friction those with branched alkyl chain ZDDPs, and a cyclohexylmethyl-based ZDDP gives markedly higher friction than non-cyclic ones. Depending on alkyl structure, boundary friction coefficient in rolling-sliding conditions can range from 0.09 to 0.14. These differences persist over long duration tests lasting up to 120 h. For secondary ZDDPs, boundary friction appears to depend less strongly on alkyl structure and in rolling-sliding conditions stabilises at ca 0.115 for the three ZDDPs studied. Experiments in which the ZDDP-containing lubricant is changed after tribofilm formation by a different ZDDP solution or a base oil indicate that the characteristic friction of the initial ZDDP tribofilm is lost almost as soon as rubbing commences in the new lubricant. The boundary friction rapidly stabilises at the characteristic boundary friction of the replacement ZDDP, or in the case of base oil, a value of ca 0.115 which is believed to represent the shear strength of the bare polyphosphate surface. The single exception is when a solution containing a cyclohexylethyl-based ZDDP is replaced by base oil, where the boundary friction coefficient remains at the high value characteristic of this ZDDP despite the fact that rubbing in base oil removes about 20 nm of the tribofilm. XPS analysis of the residual tribofilm reveals that this originates from presence of a considerable proportion of C-O bonds at the exposed tribofilm surface, indicating that not all of the alkoxy groups are lost from the polyphosphate during tribofilm formation. Very slow speed rubbing tests at low temperature show that the ZDDP solutions give boundary friction values that vary with alkyl group structure in a similar fashion to rolling-sliding MTM tests. These variations in friction occur immediately on rubbing, before any measurable tribofilm can develop. This study suggest that ZDDPs control boundary friction by adsorbing on rubbing steel or tribofilm surfaces in a fashion similar to organic friction modifiers. However it is believed that, for primary ZDDPs, residual alkoxy groups still chemically bonded to the phosphorus atoms of newly-formed polyphosphate/phosphate tribofilm may also contribute to boundary friction. This understanding will contribute to the design of low friction, fuel efficient crankcase engine oils. Graphical Abstract

Boundary Friction for a Line Contact Model: An Empirical Approach

2015 ◽  
Vol 642 ◽  
pp. 8-12
Author(s):  
William W.F. Chong ◽  
Miguel de La Cruz
Keyword(s):  
Steel Plate ◽  
Friction Model ◽  
Boundary Friction ◽  
Slider Bearing ◽  
Base Oil ◽  
Atomic Force ◽  
Alternative Approach ◽  
Nanoscale Friction ◽  
Friction Measurements ◽  
Good Agreement

The paper introduces an alternative approach to predict boundary friction for rough surfaces at micros-scale through the empirical integration of asperity-like nanoscale friction measurements. The nanoscale friction is measured using an atomic force microscope (AFM) tip sliding on a steel plate, confining the test lubricant, i.e. base oil for the fully formulated SAE grade 10w40. The approach, based on the Greenwood and Tripp’s friction model, is combined with the modified Elrod’s cavitation algorithm in order to predict the friction generated by a slider-bearing test rig. The numerical simulation results, using an improved boundary friction model, showed good agreement with the measured friction data.

Formation of Friction Layers and Wear Resistance of Steels under Conditions of Boundary Friction

2003 ◽  
Vol 39 (6) ◽  
pp. 855-862
Author(s):  
V. G. Novitskii ◽  
V. P. Gavrilyuk ◽  
D. D. Panasenko ◽  
N. A. Kal'chuk ◽  
V. Ya. Khoruzhii
Keyword(s):  
Wear Resistance ◽  
Boundary Friction

scholarly journals Wet but not slippery: boundary friction in tree frog adhesive toe pads

2006 ◽  
Vol 3 (10) ◽  
pp. 689-697 ◽  
Author(s):  
W Federle ◽  
W.J.P Barnes ◽  
W Baumgartner ◽  
P Drechsler ◽  
J.M Smith
Keyword(s):  
Boundary Friction ◽  
Tree Frog ◽  
Force Measurements ◽  
Present Evidence ◽  
Laser Tweezer ◽  
Viscous Forces ◽  
Litoria Caerulea ◽  
Filled Joint ◽  
Tree Frogs ◽  
Close Contacts

Tree frogs are remarkable for their capacity to cling to smooth surfaces using large toe pads. The adhesive skin of tree frog toe pads is characterized by peg-studded hexagonal cells separated by deep channels into which mucus glands open. The pads are completely wetted with watery mucus, which led previous authors to suggest that attachment is solely due to capillary and viscous forces generated by the fluid-filled joint between the pad and the substrate. Here, we present evidence from single-toe force measurements, laser tweezer microrheometry of pad mucus and interference reflection microscopy of the contact zone in Litoria caerulea , that tree frog attachment forces are significantly enhanced by close contacts and boundary friction between the pad epidermis and the substrate, facilitated by the highly regular pad microstructure.

scholarly journals Kinetic boundary friction

1947 ◽  
Vol 189 (1016) ◽  
pp. 88-102 ◽  
Keyword(s):  
Oleic Acid ◽  
Mineral Oil ◽  
Boundary Friction ◽  
Effect Of Temperature ◽  
Pure Substance ◽  
Relaxation Oscillations ◽  
Kinetic Friction ◽  
Fatty Oil ◽  
Frictional Forces ◽  
Kinetic Boundary

It is shown that the exhibition of smooth sliding and relaxation oscillations, or ‘stick-slips’, under conditions of boundary lubrication, when frictional forces are measured by the deflexion of an elastic system, may be explained as due to the dependence of kinetic friction on velocity. In the cases giving smooth sliding, kinetic friction decreases as velocity decreases, at very low speeds; for the cases giving relaxation oscillations kinetic friction increases as velocity decreases. That is, sliding under boundary conditions is not inherently discontinuous, any discontinuous motion being due to the dynamics of the measuring instrument, and is the result of kinetic friction increasing as velocity decreases. Curves of boundary friction against velocity, using various slicing surfaces, have been determined for a number of lubricants, which show both the above-mentioned types of friction-velocity relationship; and the dependence is shown of kinetic boundary friction on molecular weight for a series of esters of the fatty acids, on percentage of fatty oil in a compounded lubricant (actually oleic acid in mineral oil) and on temperature for a pure substance and a mineral oil. The measurements with the series of esters show some agreement with results given by Fogg (1940). The mixtures of oleic acid with mineral oil give decreasing kinetic friction with increasing percentage of oleic acid right up to 100% oleic acid. The effect of temperature on the dependence of friction in velocity shows that the temperature at which relaxation oscillations first occur depends on the speed of sliding, from which it appears that measurements of the temperature at which relaxation oscillations start at constant sliding speed (Frewing 1942) are not a measure of the temperature at which there is a discontinuity in the properties of the boundary layer.

ADSORPTION AND BOUNDARY FRICTION ON POLYMER SURFACES

1962 ◽  
Vol 66 (6) ◽  
pp. 1136-1143 ◽  
Author(s):  
Tomlinson Fort
Keyword(s):  
Polymer Surfaces ◽  
Boundary Friction

scholarly journals Kinetic friction in or near the boundary region - I. Apparatus and experimental methods

1946 ◽  
Vol 187 (1011) ◽  
pp. 430-439 ◽  
Keyword(s):  
Mixed Boundary ◽  
Film Formation ◽  
Boundary Region ◽  
Point Of View ◽  
Boundary Friction ◽  
Limiting Factor ◽  
Dead Load ◽  
Direct Reading ◽  
Resistance To Sliding ◽  
Fluid Damping

When the hydrodynamic forces in a lubricant between two sliding surfaces are insufficient to carry the load between them, the condition which occurs is one of mixed boundary and fluid lubrication. From the point of view of damage to the surfaces and of resistance to sliding, the important part is the boundary friction, which can conveniently be studied only when isolated from fluid friction. There are two methods of obtaining relatively pure boundary friction: first, to ensure that the amount of lubricant present is only sufficient to provide a boundary film, or secondly, so to control conditions of load, speed and contact area that little or no opportunity is given for fluid film formation. The relative advantages of the two methods are discussed, and apparatus is described in which the second, method is employed. In this apparatus one specimen is driven at a fixed velocity, and a second specimen is applied to it by a dead load. The force required to restrain the second specimen is measured by balancing against a variable dead load, instability being suppressed by fluid damping. A direct reading of coefficient of friction is thus obtained by a null method. Reproducibility of determinations is generally within 10%, the limiting factor being the accuracy with which exactly similar surfaces can be reproduced.

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