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 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.

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.

Adhesion and Friction of Elastomers

1981 ◽  
Vol 54 (5) ◽  
pp. 944-962 ◽  
Author(s):  
A. D. Roberts
Keyword(s):  
Surface Energy ◽  
Liquid Film ◽  
Bearing Capacity ◽  
Electrical Double Layer ◽  
Sliding Friction ◽  
Contact Region ◽  
Rolling Resistance ◽  
Load Bearing Capacity ◽  
Dry Contact ◽  
Nonequilibrium Conditions

Abstract Use of mirror smooth spheres and cylinders of rubber allows the thickness and contour of a liquid film trapped between surfaces to be studied by optical interferometry. Close normal approach reveals the load bearing capacity of electrical double layer forces. In the absence of such forces, a liquid film collapses leading to areas of adhesion over most of the contact region. The adhesion can be interpreted in terms of surface energy. The force required to separate adhered surfaces is found to depend critically upon the rate of separation. Dry contact observations reveal that under nonequilibrium conditions the apparent surface energy may be very much greater than the equilibrium energy. The observations can be used, in certain circumstances, to predict tack, rolling resistance and sliding friction. Such prediction reflects a combination of surface properties and bulk viscoelasticity of the rubber. In particular, the approach has been applied to rolling on rough surfaces and to the friction of rubber on ice.

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.

Lubricated point heavily loaded contacts of functionally graded materials. Part 1. Dry contacts

2017 ◽  
Vol 23 (7) ◽  
pp. 1061-1080 ◽  
Author(s):  
Ilya I Kudish ◽  
Sergey S Volkov ◽  
Andrey S Vasiliev ◽  
Sergey M Aizikovich
Keyword(s):  
Contact Problem ◽  
Film Thickness ◽  
Functionally Graded Materials ◽  
Functionally Graded ◽  
Elastic Materials ◽  
Graded Materials ◽  
Lubrication Film ◽  
Lubricated Contacts ◽  
Dry Contact ◽  
Lubricated Contact

Over the last couple decades coatings attract more and more attention in practical applications. The present study addresses a question which is not well studied: how coated surfaces behave in lubricated contacts? In other words, this is a study of the effectiveness of functionally graded materials in heavily loaded point elastohydrodynamically lubricated contacts with straight lubricant entrainment. As a part of the study, some criteria of coating effectiveness are introduced and discussed. More specifically, the behavior of main parameters such as the lubrication film thickness and the frictional force in point heavily loaded lubricated contacts of functionally graded elastic materials are considered. The problem is studied based on the method of matched asymptotic expansions which allows us to split the problem into two separate problems: a dry contact problems for functionally graded elastic materials and an elastohydrodynamically lubricated problem for functionally graded materials. The elastohydrodynamically lubricated problem uses as input data not only the operational and physical parameters of the materials and lubricant but also the asymptotic behavior of the dry contact problem solution near the contact boundaries. Therefore, a sequence of two problems must be solved: the dry contact problems for functionally graded elastic materials and the elastohydrodynamically lubricated problem for functionally graded materials. Similar methods have been used for the analysis of an elastohydrodynamically lubricated problem for heavily loaded line contacts of functionally graded materials. The dry contact problem will be analyzed in Part 1 of the paper based on a semi-analytical bilateral method which produces correct asymptotic solutions for thin and thick coatings. The analytical expressions for contact pressure are obtained and analyzed for various combinations of coating thicknesses and elastic properties. The elastohydrodynamically lubricated problem will be considered in Part 2 of the paper based on the method of matched asymptotic expansions. In the analysis of the elastohydrodynamically lubricated problem, as in the case of homogeneous contact materials, it is shown that the whole contact region can be subdivided into three subregions: the central one which is adjacent to the other two regions occupied by the ends of the zones. The central region can be subdivided into the Hertzian region and then adjacent to it inlet and exit zones which, in turn, are adjacent to the inlet and exit boundaries of the contact, respectively. In the Hertzian region the elastohydrodynamically lubricated problem solution is very close to the solution of the corresponding dry (i.e. non-lubricated) contact problem for functionally graded elastic materials which have been analyzed. In the central region in the inlet and exit zones of a heavily loaded point elastohydrodynamically lubricated contact, the elastohydrodynamically lubricated problem for functionally graded elastic materials using certain scaling transforms can be reduced to asymptotically valid equations identical to the ones obtained in the inlet and exit zones of heavily loaded line elastohydrodynamically lubricated contacts for homogeneous elastic materials. Therefore, many of the well known properties of heavily loaded line elastohydrodynamically lubricated contacts for homogeneous elastic materials are also valid for heavily loaded point elastohydrodynamically lubricated contacts for functionally graded elastic materials. These asymptotically valid equations can be analyzed and numerically solved based on stable methods using a specific regularization approach, which were developed for lubricated line contacts. Also, this asymptotic analysis leads to an easy analytical derivation of formulas for the lubrication film thickness which take into account the inhomogeneity of the elastic materials. As a result of this analysis, some criteria for lubrication film thickness increase and friction force reduction are proposed. These criteria depend on lubricant properties as well as the properties of functionally graded elastic materials involved in lubricated contacts. Such a sequential solution of the elastohydrodynamically lubricated problem for functionally graded materials makes it perfectly clear what the dependence is of elastohydrodynamically lubricated contact parameters on the solid material (including the coating) and lubricant properties.

Direct Micro Mechanical Testing Method for MEMS Materials

2005 ◽  
Author(s):  
Bo Li ◽  
Quanfang Chen
Keyword(s):  
Mechanical Testing ◽  
Fracture Strength ◽  
Mechanical Test ◽  
Optimized Design ◽  
Element Analysis ◽  
Specimen Handling ◽  
Micro Scale ◽  
Brittle Behavior ◽  
Testing Method ◽  
Simple Boundary

Mechanical properties of MEMS materials are crucial for MEMS performance and reliability. Micro scale mechanical test has been challenging to MEMS community, due to the difficulties in handling micro scale specimens. In this article, a novel micro mechanical tensile testing method has been developed in combining a stiff microscale specimen developed with MTS Tytron Micro Force Tester. The advantages of this method include that it is a standard direct test of micro machined specimens, simple boundary conditions, and easy specimen handling/mounting in characterization. A novel specimen with micro features has been designed and fabricated for the direct mechanical testing. The specimen consists of three micro beams in parallel. The width of the center beam is 40 μm and the outer two beams’ width is 90 μm. The length of all three beams is 4 mm long. An optimized design has been achieved with finite element analysis, which shows that 98% of the total deformation occurs on the beams’ gage length. The stress is uniformly distributed over the three beams with a difference less than 0.5% among them. Both UV-LIGA fabricated nickel and SU-8 specimens have been tested. The UV-LIGA fabricated nickel has fracture strength of 1000±70 MPa and the results of SU-8 show a brittle behavior with fracture strength of 48±3 MPa.

Benchmarking of Direct and Indirect Friction Tests in Micro Forming

2012 ◽  
Vol 504-506 ◽  
pp. 581-586 ◽  
Author(s):  
Rasmus Solmer Eriksen ◽  
M. Calaon ◽  
Mogens Arentoft ◽  
Nils Bay
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Visual Inspection ◽  
Sliding Friction ◽  
Continuous Measurement ◽  
Work Piece ◽  
Friction Test ◽  
Micro Forming ◽  
Micro Scale ◽  
Flat Tool

In this study the application of a simulative sliding friction test at micro scale is suggested. Two work piece specimens are upset against opposing sides of a flat tool element. The tool element is then pulled out while the resulting friction force F is measured. The test principle offers several advantages when compared against the DEC-test, including easy visual inspection of tool and work piece surfaces, continuous measurement of friction coefficient over the complete sliding length and less sensitivity to mechanical tolerance deviations of work piece and tool elements.

Effect of Sliding Friction on Contact Stresses in a Rectangle Compressed by Rigid Planes

1975 ◽  
Vol 42 (3) ◽  
pp. 656-662 ◽  
Author(s):  
S. N. Prasad ◽  
S. Dasgupta
Keyword(s):  
Aspect Ratio ◽  
Plane Strain ◽  
Integral Equations ◽  
Coefficient Of Friction ◽  
Contact Area ◽  
Sliding Friction ◽  
Practical Interest ◽  
Slip Zone ◽  
Surface Displacements ◽  
Frictional Coefficients

The plane-strain compression of an elastic rectangle by rigid, rough planes with finite coefficient of friction between the surfaces is considered. The contact area is divided into an inner adhesive region in which the surface displacements are known, surrounded by regions in which the friction is limiting and the displacement parallel to the interface is not known. The remaining set of parallel edges of the rectangle is free from tractions. The problem is formulated in terms of Papkovich-Fadle eigenfunctions which lead to the solution of a set of two integral equations of the second kind. Solution of the integral equations which satisfies the finiteness of stresses at the point which separates the adhesive from the slip zone, determines the extent of adhesion. This is found to be independent of the magnitude of load, but depends on the values of frictional coefficients, Poisson’s ratio and the aspect ratio. Numerical results of the quantities of practical interest are reported.

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