Developing a Computational Model for Shoe-Floor Friction

Details

• Personal Author:
  Beschorner K ; Redfern M
• Description:
  Slip and fall accidents are among the leading and fastest growing sources of occupational injuries. Slip and fall accidents typically occur when the available friction between the shoe and the floor is less than the friction that is required during walking or performing some task. Existing methods of evaluating shoe and floor slip-resistance are limited to using tribometers to measure the coefficient of friction (COF). This approach is limited because COF is a gross approximation of several tribological mechanisms and cannot guide interventions. Over the past four years, our team has created shoe-floor friction models and performed experimental studies to identify and quantify the underlying tribological contributions to shoe-floor COF. These studies were performed at the microscopic scale (Aim 1), the whole-shoe scale (Aim 2) and during laboratory studies of human subjects (Aim 3). These studies revealed two mechanisms by which fluid contaminants can cause a slip: hydrodynamic lubrication and boundary lubrication. Each was explored from the microscopic level through to human biomechanical slip evaluations. Hydrodynamic lubrication occurs when fluid between the shoe and the floor becomes pressurized and reduces COF. This effect was confirmed by fluid modeling and experimental studies at the microscopic scale, experimental studies at the whole shoe scale, and by human slipping studies. Specifically, at the microscopic scale, shoe-floor COF decreased with increasing sliding speed and fluid viscosity consistent with the film thickness that were estimated by hydrodynamic models. At the whole-shoe scale, a novel method of measuring under-shoe fluid pressures was implemented to evaluate the factors that influence hydrodynamic lubrication. Shoe tread and fluid viscosity were identified as the critical factors influencing under-shoe fluid pressures. The finding that shoe tread reduces under-shoe fluid pressures and slipping risk was confirmed in human subject studies using an unexpected slipping paradigm. Boundary lubrication occurs when a fluid does not become pressurized but still reduces the COF between the surfaces. The two main contributors to boundary lubrication friction were identified as adhesion and hysteresis COF. High viscosity fluid contaminants drastically reduced the adhesion COF and caused the shoe-floor interface to become slippery. Adhesion in the presence of a fluid was modeled as a function of the fluid and the amount of dry adhesion at the microscopic model. Furthermore, finite element analysis was used to model the amount of dry adhesion and hysteresis friction at the microscopic scale. This model showed strong correlation with experimental data. Furthermore, this model was used to explain the independent effects of shoe hardness, roughness, floor roughness, speed and vertical loading on coefficient of friction. Boundary lubrication COF values for different shoe materials were found to predict slipping risk using a human-slipping paradigm, confirming the relevance of this mechanism for shoe-floor friction. The findings from this study can be applied to improve shoe design, selection and maintenance. For example, shoes that maintain a rough outsole and that contain at least 1.5 mm of tread will reduce fluid pressures and maximize boundary lubrication COF for environments that commonly experience greasy or oily contaminants (i.e., restaurant kitchens). [Description provided by NIOSH]
• Subjects:
  Accidental Falls Accidents Biomechanical Phenomena Microbiology Occupational Health Occupational Injuries Safety
• Keywords:
  Biomechanical Modeling Biomechanics Microscopic Analysis Occupational Accidents Slips, Trips, And Falls STF Walking Surfaces
• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  OSHA Region 3 ; Pennsylvania
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-71
• NIOSHTIC Number:
  nn:20055602
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008986, 2014 Oct; :1-71
• Contact Point Address:
  Mark Redfern, Ph.D., University of Pittsburgh, 826 Cathedral of Learing, Pittsburgh, PA 15260
• Email:
  mredfern@pitt.edu
• Federal Fiscal Year:
  2015
• NORA Priority Area:
  Manufacturing ; Services
• Performing Organization:
  University of Pittsburgh at Pittsburgh
• Peer Reviewed:
  False
• Start Date:
  20100801
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20140731
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:e37cf13e0aba0cf0b7a102ff144de8a31fc25a8cb3e8582e47e5f902f98aa988d1f0796b767a5bd3ef5cc9c5abb9a424d6eb8cd225ee569d66cc5bd635f13d04
• Download URL:
  https://stacks.cdc.gov/view/cdc/218855/cdc_218855_DS1.pdf
• File Type:
  [PDF - 2.09 MB ]