scholarly journals Evidence that abrasion can govern snow kinetic friction

2021 ◽  
Author(s):  
James Lever ◽  
Susan Taylor ◽  
Garrett Hoch ◽  
Charles Daghlian
Keyword(s):  
Practical Interest ◽  
Field Tests ◽  
Frictional Heat ◽  
Scanning Electron Micrographs ◽  
Wear Particles ◽  
Kinetic Friction ◽  
Low Friction ◽  
Dry Contact ◽  
Lubricated Contact ◽  
Theoretical Evidence

The long-accepted theory to explain why snow is slippery postulates self-lubrication: frictional heat from sliding melts and thereby lubricates the contacting snow grains. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. Here we provide additional observational and theoretical evidence that abrasion can govern snow kinetic friction. We obtained coordinated infrared, visible-light and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests. Importantly, published measurements of interface temperatures also indicate that melting did not occur during field tests on sleds and skis. Although prevailing theory anticipates a transition from dry to lubricated contact along a slider, we suggest that dry-contact abrasion and heat flow can prevent this transition from occurring for snow-friction scenarios of practical interest.

scholarly journals Evidence that abrasion can govern snow kinetic friction

2018 ◽  
Vol 65 (249) ◽  
pp. 68-84
Author(s):  
JAMES H. LEVER ◽  
SUSAN TAYLOR ◽  
GARRETT R. HOCH ◽  
CHARLES DAGHLIAN
Keyword(s):  
Practical Interest ◽  
Field Tests ◽  
Frictional Heat ◽  
Scanning Electron Micrographs ◽  
Wear Particles ◽  
Kinetic Friction ◽  
Low Friction ◽  
Dry Contact ◽  
Lubricated Contact ◽  
Theoretical Evidence

ABSTRACTThe long-accepted theory to explain why snow is slippery postulates self-lubrication: frictional heat from sliding melts and thereby lubricates the contacting snow grains. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. Here we provide additional observational and theoretical evidence that abrasion can govern snow kinetic friction. We obtained coordinated infrared, visible-light and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area, and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests. Importantly, published measurements of interface temperatures also indicate that melting did not occur during field tests on sleds and skis. Although prevailing theory anticipates a transition from dry to lubricated contact along a slider, we suggest that dry-contact abrasion and heat flow can prevent this transition from occurring for snow-friction scenarios of practical interest.

Why is Snow Slippery? The Role of Abrasion in Snow Kinetic Friction

2020 ◽  
Author(s):  
James Lever ◽  
Susan Taylor ◽  
Garrett Hoch ◽  
Emily Asenath-Smith
Keyword(s):  
Field Tests ◽  
Ice Crystals ◽  
Lubricant Layer ◽  
Scanning Electron Micrographs ◽  
Wear Particles ◽  
Kinetic Friction ◽  
Low Friction ◽  
Dry Contact ◽  
Theoretical Analyses

<p>The mechanics of snow friction are central to competitive skiing, safe winter driving, avalanche dynamics, and efficient Polar sleds. For nearly 80 years, prevailing theory has postulated self-lubrication: dry-contact sliding warms snow-grains to the melting point, and further sliding produces melt-water that lubricates the interface. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. We obtained coordinated infrared, visible-light, and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area, and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests. Importantly, published measurements of interface temperatures also indicate that melting did not occur during field tests on sleds and skis. We postulate that abraded ice crystals form a dry-lubricant layer that makes contacting snow-grains slippery and are currently undertaking additional observations and theoretical analyses to assess this hypothesis.</p>

scholarly journals The mechanics of snow friction as revealed by micro-scale interface observations

2017 ◽  
Vol 64 (243) ◽  
pp. 27-36 ◽  
Author(s):  
JAMES H. LEVER ◽  
SUSAN TAYLOR ◽  
ARNOLD J. SONG ◽  
ZOE R. COURVILLE ◽  
ROSS LIEBLAPPEN ◽  
...  
Keyword(s):  
Melting Point ◽  
High Resolution ◽  
Real Contact Area ◽  
Kinetic Friction ◽  
Low Friction ◽  
Dominant Mechanism ◽  
Micro Scale ◽  
Real Contact ◽  
Dry Contact ◽  
Air Pockets

ABSTRACTThe mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 µm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction.

Assessing the mechanisms thought to govern ice and snow friction and their interplay with substrate brittle behavior

2021 ◽  
Author(s):  
James Lever ◽  
Emily Asenath-Smith ◽  
Susan Taylor ◽  
Austin Lines
Keyword(s):  
Sliding Friction ◽  
Practical Interest ◽  
Water Film ◽  
Interaction Length ◽  
Winter Sports ◽  
Micro Scale ◽  
Brittle Behavior ◽  
Single Mechanism ◽  
Dry Contact ◽  
Lubricated Contact

Sliding friction on ice and snow is characteristically low at temperatures common on Earth’s surface. This slipperiness underlies efficient sleds, winter sports, and the need for specialized tires. Friction can also play micro-mechanical role affecting ice compressive and crushing strengths. Researchers have proposed several mechanisms thought to govern ice and snow friction, but directly validating the underlying mechanics has been difficult. This may be changing, as instruments capable of micro-scale measurements and imaging are now being brought to bear on friction studies. Nevertheless, given the broad regimes of practical interest (interaction length, temperature, speed, pressure, slider properties, etc.), it may be unrealistic to expect that a single mechanism accounts for why ice and snow are slippery. Because bulk ice, and the ice grains that constitute snow, are solids near their melting point at terrestrial temperatures, most research has focused on whether a lubricating water film forms at the interface with a slider. However, ice is extremely brittle, and dry-contact abrasion and wear at the front of sliders could prevent or delay a transition to lubricated contact. Also, water is a poor lubricant, and lubricating films thick enough to separate surface asperities may not form for many systems of interest. This article aims to assess our knowledge of the mechanics underlying ice and snow friction.

scholarly journals Assessing the Mechanisms Thought to Govern Ice and Snow Friction and Their Interplay With Substrate Brittle Behavior

2021 ◽  
Vol 7 ◽  
Author(s):  
James H. Lever ◽  
Emily Asenath-Smith ◽  
Susan Taylor ◽  
Austin P. Lines
Keyword(s):  
Sliding Friction ◽  
Practical Interest ◽  
Water Film ◽  
Winter Sports ◽  
Brittle Behavior ◽  
Single Mechanism ◽  
Dry Contact ◽  
Key Issues ◽  
Pressure Melting ◽  
Lubricated Contact

Sliding friction on ice and snow is characteristically low at temperatures common on Earth’s surface. This slipperiness underlies efficient sleds, winter sports, and the need for specialized tires. Friction can also play a micro-mechanical role affecting ice compressive and crushing strengths. Researchers have proposed several mechanisms thought to govern ice and snow friction, but directly validating the underlying mechanics has been difficult. This may be changing, as instruments capable of micro-scale measurements and imaging are now being brought to bear on friction studies. Nevertheless, given the broad regimes of practical interest (interaction length, temperature, speed, pressure, slider properties, etc.), it may be unrealistic to expect that a single mechanism accounts for why ice and snow are slippery. Because bulk ice, and the ice grains that constitute snow, are solids near their melting point at terrestrial temperatures, most research has focused on whether a lubricating water film forms at the interface with a slider. However, ice is extremely brittle, and dry-contact abrasion and wear at the front of sliders could prevent or delay a transition to lubricated contact. Also, water is a poor lubricant, and lubricating films thick enough to separate surface asperities may not form for many systems of interest. This article aims to assess our knowledge of the mechanics underlying ice and snow friction. We begin with a brief summary of the mechanical behavior of ice and snow substrates, behavior which perhaps has not received sufficient attention in friction studies. We then assess the strengths and weaknesses of five ice- and snow-friction hypotheses: pressure-melting, self-lubrication, quasi-liquid layers, abrasion, and ice-rich slurries. We discuss their assumptions and review evidence to determine whether they are consistent with the postulated mechanics. Lastly, we identify key issues that warrant additional research to resolve the specific mechanics and the transitions between them that control ice and snow friction across regimes of practical interest.

scholarly journals The mechanics of snow friction as revealed by micro-scale interface observations

2021 ◽  
Author(s):  
James Lever ◽  
Susan Taylor ◽  
Arnold Song ◽  
Zoe Courville ◽  
Ross Lieblappen ◽  
...  
Keyword(s):  
Melting Point ◽  
High Resolution ◽  
Real Contact Area ◽  
Kinetic Friction ◽  
Low Friction ◽  
Dominant Mechanism ◽  
Micro Scale ◽  
Real Contact ◽  
Dry Contact ◽  
Air Pockets

The mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 μm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction.

Effect of PTFE Retainer on Friction Coefficient in Polymer Thrust Bearings under Dry Contact

2013 ◽  
Vol 683 ◽  
pp. 90-93 ◽  
Author(s):  
Koshiro Mizobe ◽  
Takashi Honda ◽  
Hitonobu Koike ◽  
Edson Costa Santos ◽  
Yuji Kashima ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Fatigue Tests ◽  
Rolling Contact ◽  
Low Friction ◽  
Friction Forces ◽  
Thrust Bearings ◽  
Dry Contact

Polyetheretherketone (PEEK) is a tough semi-crystalline thermoplastic polymer with excellent mechanical properties. While abilities of polyphenylenesulfide (PPS) are similar to PEEK, former material cost was lower than later. Polytetrafluoroethylene (PTFE) is well known because of its low friction coefficient and self lubrication ability. The objective of this study is to observe the friction coefficient of hybrid bearings, PTFE retainer sandwiched with PPS-races or PEEK-races. Rolling contact fatigue tests were performed and in situ friction forces wear measured. It is concluded that the PTFE retainer reduced friction coefficient.

Microgeometry of sliding surfaces and wear particles in lubricated contact

Wear ◽  
1984 ◽  
Vol 100 (1-3) ◽  
pp. 33-45 ◽  
Author(s):  
Yoshitsugu Kimura ◽  
Joichi Sugimura
Keyword(s):  
Wear Particles ◽  
Sliding Surfaces ◽  
Lubricated Contact

RECENT ADVANCES IN DISPERSANT EFFECTIVENESS EVALUATION: EXPERIMENTAL AND FIELD ASPECTS

1985 ◽  
Vol 1985 (1) ◽  
pp. 445-452 ◽  
Author(s):  
J. P. Desmarquest ◽  
J. Croquette ◽  
F. Merlin ◽  
C. Bocard ◽  
G. Castaing ◽  
...  
Keyword(s):  
Laboratory Tests ◽  
Oil Spills ◽  
Practical Interest ◽  
Field Tests ◽  
Field Trials ◽  
Large Field ◽  
Experimental Program ◽  
Experimental Conditions ◽  
Good Accord ◽  
Dispersant Effectiveness

ABSTRACT Although dispersants are used in different countries, it appeared from recent international meetings that more knowledge concerning dispersant effectiveness is still needed for a better response to oil spills. Large field trials which were conducted during the past two years raised some questions as to how dispersants work at sea. Even though the results obtained in different laboratory tests are generally in good accord, significant discrepancies of practical interest may be observed because of variations in the experimental conditions. With EEC support, an experimental program has been conducted by CEDRE and Institut Français du Pétrole (IFP), both with the already-described French middle scale field test and with different laboratory tests (U.K. and French standard tests and the recently developed dilution test). With the objective of correlating the results obtained in field tests and in laboratory tests, several parameters were investigated at sea with different dispersants: the type and viscosity of the oil, slick thickness, and oil to dispersant ratio. Based mainly on the results obtained in the laboratory with dilution tests, new aspects of dispersant behavior have been identified, relating to the nature of the oil and the energy input.

Temperature Rise Simulation of Three-Dimensional Rough Surfaces in Mixed Lubricated Contact

1998 ◽  
Vol 120 (2) ◽  
pp. 310-318 ◽  
Author(s):  
Liangheng Qiu ◽  
Herbert S. Cheng
Keyword(s):  
Temperature Rise ◽  
Surface Film ◽  
Computing Time ◽  
Three Dimensional ◽  
Film Surface ◽  
Grid Method ◽  
Lubricant Film ◽  
Frictional Heat ◽  
Asperity Contact ◽  
Lubricated Contact

A numerical simulation of the temperature rise for a three-dimensional rough surface sliding against a smooth surface in mixed lubricated contact has been developed. The effects of lubricant film friction and solid asperity friction are considered in the simulation. The moving grid method, which greatly reduces the required computer memory size and computing time, is used to solve the coefficient matrix of temperature equations. The time-dependent surface temperature rise at very small subregions is obtained. Different friction coefficients for lubricant shearing, surface film shearing and dry solid asperity contact are used to simulate the change of frictional heat in mixed lubricated contact. A critical temperature criterion is used to determine whether the friction coefficient is controlled by lubricant film, surface film, or dry solid asperity contact. Solutions for different contact conditions are presented for verification of the present simulation

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