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Analysis of Shoe Friction During Sliding Against Floor Material: Role of Fluid Contaminant

[+] Author and Article Information
Caitlin T. Moore, Pradeep L. Menezes, Michael R. Lovell

 Department of Industrial Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53201

Kurt E. Beschorner1

 Department of Industrial Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53201beschorn@uwm.edu

1

Corresponding author.

J. Tribol 134(4), 041104 (Sep 04, 2012) (7 pages) doi:10.1115/1.4007346 History: Received March 24, 2011; Revised June 23, 2012; Published September 04, 2012; Online September 04, 2012

Understanding the tribological interactions between shoe and floor materials is important in order to enhance shoe and floor design and to prevent slip and fall accidents during walking. In the present investigation, experiments were conducted using a custom developed pin-on-disk type tribometer to understand the influence of boundary and hydrodynamic properties on the shoe-floor materials’ coefficient of friction. Specifically, polyurethane shoe material was slid against vinyl floor material in the presence of varying lubricants (i.e., water, detergent, three diluted glycerol concentrations, and canola oil). The experiments were conducted for a range of biologically relevant sliding velocities from 0.05 m sec−1 to 1.0 m sec−1 at a contact pressure of 266.1 kPa under ambient conditions. The fluid chemical composition appeared to affect the boundary friction coefficient with longer-chain molecules resulting in a decreased coefficient of friction. As fluid viscosity increased, the rate of coefficient of friction decay increased with respect to increasing fluid entrainment velocity, suggesting less material contact and increased film thickness. The nondimensional film thickness under all conditions was calculated and the nondimensional film thickness consistently increased with increased viscosity and speed. Additionally, the effect of functionally achievable variations in polyurethane shoe roughness on the coefficient of friction was examined and found to have no statistically significant effect on boundary or hydrodynamic contributions to the coefficient of friction.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Custom pin-on-disk tribometer used to measure the shoe-floor-contaminant coefficient of friction: (a) photograph, and (b) schematic showing floor material (disk), shoe material (pin), and the direction of the shear and normal forces used to calculate the coefficient of friction

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Figure 2

Typical time-history of the coefficient of friction

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Figure 3

Variation of the coefficient of friction with speed (triangles) for 25% glycerol-75% water lubrication and 8.2 μm shoe roughness; the solid line represents the exponential regression fit. The values obtained for the variables of Eq. 1 are COFBL  = 0.839, τhydro  = 0.184, and COFasymptote  = 0.164.

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Figure 4

Example of a surface profile fit with a second-order polynomial to calculate the reduced radius of curvature (R′); the dotted line shows the measured surface profile and the solid line is the second-order polynomial regression fit to the data

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Figure 5

Master curve of all COF data collected across all experiments plotted with respect to viscosity*speed

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Figure 6

Average exponential regression fits of average COF data under water, detergent, 25% glycerol-75% water, and 50% glycerol-50% water lubrication

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Figure 7

Average COFBL with standard deviations for water, detergent, 25% glycerol-75% water, 50% glycerol-50% water, 75% glycerol-25% water, and canola oil

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Figure 8

Calculated nondimensional film thickness with increasing speed for water, detergent, 25% glycerol-75% water, 50% glycerol-50% water, 75% glycerol-25% water, and canola oil lubricants. (Note: the nondimensional film thickness of detergent and 25% glycerol-75% water are very close and therefore appear merged).

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Figure 9

Average τhydro with standard deviations for water, detergent, 25% glycerol-75% water, and 50% glycerol-50% water lubrication

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