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38 ReferencesThe Role of Friction in the Measurement of Slipperiness, Part 2: Survey of Friction Measurement Devices
Abstract
This paper seeks to address questions related to friction measurement such as how friction is related to human-centred assessment and actual slipping, and how repeatable friction measurements are. Commonly used devices for slipperiness measurement are surveyed and their characteristics compared with suggested test conditions from biomechanical observations summarized in Part 1. The issues of device validity, repeatability, reproducibility and usability are examined from the published literature. Friction assessment using the mechanical measurement devices described appears generally valid and reliable. However, the validity of most devices could be improved by bringing them within the range of human slipping conditions observed in biomechanical studies. Future studies should clearly describe the performance limitations of any device and its results and should consider whether the device conditions reflect these actual human slipping conditions. There is also a need for validation studies of more devices by walking experiments.
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- These problems further complicate efforts in the development of interventions evaluated with friction measurements. As pointed out by Chang et al. (2001aChang et al. ( , 2001b), the measurement conditions of these devices are still far from perfect as compared with the biomechanical data reported in the literature and are inconsistent across various devices. Bio-fidelity of these devices remains a critical issue.
[Show abstract] [Hide abstract] ABSTRACT: Occupational slips, trips and falls on the same level (STFL) result in substantial injuries worldwide. This paper summarises the state of science regarding STFL, outlining relevant aspects of epidemiology, biomechanics, psychophysics, tribology, organisational influences and injury prevention. This review reaffirms that STFL remain a major cause of workplace injury and STFL prevention is a complex problem, requiring multi-disciplinary, multi-faceted approaches. Despite progress in recent decades in understanding the mechanisms involved in STFL, especially slipping, research leading to evidence-based prevention practices remains insufficient, given the problem scale. It is concluded that there is a pressing need to develop better fall prevention strategies using systems approaches conceptualising and addressing the factors involved in STFL, with considerations of the full range of factors and their interactions. There is also an urgent need for field trials of various fall prevention strategies to assess the effectiveness of different intervention components and their interactions. Practitioner Summary: Work-related slipping, tripping and falls on the same level are a major source of occupational injury. The causes are broadly understood, although more attention is needed from a systems perspective. Research has shown preventative action to be effective, but further studies are required to understand which aspects are most beneficial.- According to the Reynolds equation, the two primary contributing factors to hydrodynamic effects are squeeze-film (Equation (1b)), where a film thickness (h) and pressure develops in the fluid as it is squeezed out from the interface during shoe loading (Strandberg, 1985; Chang et al., 2001), and the wedge effect (Equation (1c)), where the motion of the shoe over the floor surface causes fluid film thickness (h) and pressure to develop in the shoe–floor interface (Proctor & Coleman , 1988; Chang et al., 2001; Beschorner et al., 2009). Previous shoe–floor–fluid modeling studies have relied on the assumption that a pressurized fluid film layer, as described by the Reynolds equation, exists between the shoe and the floor (Batterman et al., 2004; Beschorner et al., 2009).
[Show abstract] [Hide abstract] ABSTRACT: OCCUPATIONAL APPLICATIONS This study introduces a method for measuring fluid pressures in the shoe–floor interface. The novel method was then applied to shoes with varying tread depths. The rationale for this approach is that measuring fluid pressures can help to identify the reason for low friction and guide interventions for increasing slip resistance. High fluid pressures were observed in the absence of tread and the presence of high viscosity fluids. Fluid pressures were negligibly small when at least 1.5 mm of tread depth was present or when a low viscosity fluid was present. This study indicates that shoe tread is effective at channeling fluid out from the shoe–floor interface in the presence of highly viscous fluids. The presented methodology may be suitable for testing the performance of tread designs and establishing wear limits for shoe replacement.- Tests were carried out under a normal load of 20.9 N in ambient conditions, resulting in a biofidelic contact pressure of approximately 266.1 kPa[10], and at a singleFig. 1Custom pin-on-disk tribometer used to measure shoe–floor-contaminant friction a photograph, b schematic showing floor material (disk), shoe material (pin), and direction of shear and normal sliding speed of 0.01 m s-1 selected to be low enough to ensure boundary lubrication.
[Show abstract] [Hide abstract] ABSTRACT: Slip and fall accidents cause frequent occupational injuries. Despite recent evidence that boundary lubrication is relevant to slipping, few studies have examined the mechanisms that contribute to shoe–floor friction in this lubrication regime. This study aims to identify the contributions of adhesion and hysteresis to friction in boundary lubrication. Three shoe materials (40 Shore A hardness polyurethane, 60 Shore A hardness rubber, and 70 Shore A hardness rubber), two floor materials (vinyl and marble), and six lubricants (water, 1.5 % detergent, 25 % glycerol–75 % water, 50 % glycerol–50 % water, 75 % glycerol–25 % water, and canola oil) were tested at a single sliding speed (0.01 m s−1). Dry adhesion and hysteresis were quantified for each of the shoe–floor combinations and lubricated adhesion was quantified for all shoe–floor-fluid combinations. The contribution of adhesion and hysteresis to shoe–floor-lubricant friction was affected by both the shoe and floor material due to differences in hardness and roughness. Lubricated adhesion was complex and multifactorial with contributions from the shoe, fluid, shoe–floor interaction, floor-lubricant interaction, and shoe-lubricant interactions. A simple regression model including two fluid coefficients and the dry adhesion friction force was able to predict 49 % of the lubricated adhesion friction variability.- Translational sliding friction approaches, such as drag-sled test and incline-plane test, are widely used for static friction tests on flat metallic surfaces. Although such approaches are simple and easy to operate, the weight-induced contact pressure is considerably low ( $ 0.4 MPa) [11] [14]. Another known method is the centrifugal friction apparatus (CFA) that measures the static friction coefficient between flat surfaces by the centripetal force experienced by a rotating object [15] [16].
[Show abstract] [Hide abstract] ABSTRACT: Contact friction is present on interacting surfaces of steel thin-walled structural members under axial folding during vehicle crash, and often occurs under relatively high contact pressure (∼100 MPa) and sliding velocity (∼6 m/s). The contact friction could affect structural deformation mode and kinetic energy absorption capacity, and yet has not received sufficient attention in the area of automotive crashworthiness. The lack of knowledge on contact friction behavior and friction data of sheet metal has long affected the reliability and predictability of vehicle crash simulations. The objective of this study is to develop an appropriate experimental method for friction measurement on self-paired sheet metal under high contact pressure conditions. A fixture is designed for applying clamping pressure of 1–100 MPa on contact interfaces, under which sliding friction is generated by additional loading devices. Using a standard material test machine and a drop tower, two experimental configurations are set up for measuring the friction properties of steel sheet couples under the pressures of 1–100 MPa and the sliding velocities of 0–6 m/s. The test method is proved to be valid and viable in friction tests on a typical high-strength steel sheet. The results show distinct friction behaviors of the high steel under different loading conditions, which has also been discussed.- Combining Eqs. [7] and [8] yields the relationship between the nominal film thickness and the average gap film thickness:
[Show abstract] [Hide abstract] ABSTRACT: While slip-and-fall accidents are a serious health concern, few attempts have been made to tribologically model the shoe-floor-contaminant interface. To this end, modeling techniques are introduced here for shoe and floor materials operating in mixed lubrication. The proposed analytical model results are compared with experimental data in order to assess the validity of the developed model. Coefficient of friction (COF) values are generated using a pin-on-disk apparatus across a range of sliding speeds with two different shoe materials operating in the mixed-lubrication regime. The model solves for the contact condition using Hertzian contact mechanics theory and the hydrodynamic pressure condition using the Reynolds equation. The amount of contact deformation is adjusted iteratively such that the summed force from the fluid and contacting asperities is equivalent to the total normal force. The model predicts friction values based on the proportion of the load supported by the fluid versus the proportion of the load supported by contacting asperities. The model-generated COF-velocity plots showed close agreement with experimental values for both shoe materials studied. In addition, the model predicts that as the speed between the surfaces increases, the hydrodynamic lift increases. This in turn decreases the contact area and the load borne by the contacting surfaces. Hence, the model presented serves as an initial step towards developing shoe-floor-contaminant friction models.- This results in a near constant force between the slider and the surface. The SRT device can be used for floor testing on dry, wet and contaminated surfaces but measurements can be affected if the slider hits a bump in a relief surface at the moment of impact (Chang et al., 2001b). Static or dynamic COF testing without impact, i.e. test methods applying constant load, tend to lead to poorer separation of the interacting surfaces due to lower hydrodynamic pressure generation in the contaminant film (Moore, 1972).
[Show abstract] [Hide abstract] ABSTRACT: Unhealthy legs and claws in pig production are a persistent problem, a primary reason for which seems to be inappropriate floor properties in the pig pen. Inadequate frictional properties or low coefficient of friction (COF) may result in slippery floors and slip injuries to pigs. This thesis presents basis of design criteria for pig house floors with the aim of minimising the number of claw disorders. Parameter values were determined by pig gait studies in a gait analysis laboratory, where the pigs walked a straight or a curved test aisle. The gait was recorded by a force plate and a perpendicularly placed digital video camera as the pigs walked the test aisle. The specific aims of the four studies included in the thesis were to: 1) characterise pig gait and describe the effect of clean and fouled floor conditions for pigs walking a line on solid concrete, walking a curve on solid concrete and walking a curve on rubber mat; 2) determine the utilised COF (UCOF) of the walking pigs and compare it with measured dynamic COF (DCOF); and 3) analyse pig slip in different floor conditions. A set of parameter values characterising pig gait in clean and fouled concrete floor conditions were obtained by kinematic and kinetic methods. The data showed that pigs walking a straight line adapted their gait to fouled floor conditions. Pigs were able to adapt to walking a curve in clean floor conditions but the observed adaptation was not enough for safe walking in fouled floor conditions, where UCOF exceeded DCOF. Walking a curve on fouled rubber mat gave better traction and reduced forward and backward slips by over 50% compared with walking a curve on fouled concrete. The discrepancy between UCOF and measured DCOF observed in the studies could be due to the friction measuring device underestimating the actual risk of slipping and falling in fouled floor conditions, especially when walking a curve. Additional studies are needed to provide pig producers with more detailed information, e.g. guidelines for required COF values in pig pen situations where the required motion and speed of motion are determined. An appropriate data set for COF measurements at farm level can bring safer and more slip-resistant floor solutions in the future.
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