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12 ReferencesThe effect of filtering processes on surface roughness parameters and their correlation with the measured friction, Part II: Porcelain tiles
Abstract
It is known that surface roughness affects friction, but it is unclear which surface characteristics are better correlated with friction. Moreover, the filter process used in a surface roughness measurement affects the values of surface parameters and, therefore, affects surface representations. The effect of filter selection on the surface parameters of unglazed quarry tiles and their correlation with the measured friction was investigated in Part I. Same analyses were applied to the surface parameters of porcelain tiles and the dynamic friction coefficient measured with a pin-on-disk tester. Similar to Part I, the results indicated that some parameters, such as Sm, were significantly affected by both the filter type and band width, while some other parameters, such as Δa, were significantly affected by the band width. The filter type 2CR PC could generate surface parameters that had slightly higher linear correlation coefficients with friction than the other two filter types, but the differences in correlation coefficients due to different filter selections were significant for the surface parameters Rp and Rpm. The filter band width of 1000 is not recommended. The surface parameter Δa had a very small location dependence and a very high correlation coefficient with friction.
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- In fact, because each testing instrument has different concepts, systemic parameters and mechanical principles, it can be misleading to adopt a reference COF value without any citation to the instrument used for the slip resistance measures. Recent studies have highlighted the importance of surface roughness on slip resistance evaluations and measured a number of surface roughness parameters to identify any correlations between the surface coarseness and slip resistance properties (Harris and Shaw, 1988; Proctor and Coleman, 1988; Stevenson et al., 1989; Manning et al., 1991; Proctor, 1993; Manning and Jones, 1994; Grönqvist, 1995; Jones et al., 1995; Rowland et al., 1996; Wilson, 1996; Manning et al., 1998; Chang, 1998 Chang, , 1999 Chang, , 2000 Chang, , 2001 Chang, , 2002 Fendley et al., 1999; Chang and Matz, 2000; Smith, 2000, 2003; Kim et al., 2001; Kim, 2004a,b; Kim, 2006a,b; Kim and Nagata, 2008a,b). As stated in those studies, there are convincing evidences that surface roughness on the shoe and floor surfaces affect slipperiness significantly.
[Show abstract] [Hide abstract] ABSTRACT: Literature has shown a general trend that slip resistance performance improves with floor surface roughness. However, whether slip resistance properties are linearly correlated with surface topographies of the floors or what roughness levels are required for effective slip resistance performance still remain to be answered. This pilot study aimed to investigate slip resistance properties and identify functional levels of floor surface roughness for practical design applications in reducing the risk of slip and fall incidents. A theory model was proposed to characterize functional levels of surface roughness of floor surfaces by introducing a new concept of three distinctive zones. A series of dynamic friction tests were conducted using 3 shoes and 9 floor specimens under clean-and-dry as well as soapsuds-covered slippery wet environments. The results showed that all the tested floor-shoe combinations provided sufficient slip resistances performance under the clean-and-dry condition. A significant effect of floor type (surface roughness) on dynamic friction coefficient (DFC) was found in the soapsuds-covered wet condition. As compared to the surface roughness effects, the shoe-type effects were relatively small. Under the soapsuds-covered wet condition, floors with 50 μm in Ra roughness scale seemed to represent an upper bound in the functional range of floor surface roughness for slip resistance because further increase of surface roughness provided no additional benefit. A lower bound of the functional range for slip resistance under the soapsuds-covered wet condition was estimated from the requirement of DFC > 0.4 at Ra ≅ 17 μm. Findings from this study may have potential safety implications in the floor surface design for reducing slip and fall hazards.- [Show abstract] [Hide abstract] ABSTRACT: Surface roughness has been shown to have substantial effects on the slip resistance between shoe heels and floor surfaces under various types of walking environments. This paper summarizes comprehensive views of the current understanding on the roles of surface roughness on the shoe and floor surfaces in the measurement of slipperiness and discusses promising directions for future research. Various techniques and instruments for surface roughness measurements and related roughness parameters are reviewed in depth. It is suggested that a stylus-type profilometer and a laser scanning confocal microscope are the preferred instruments for surface roughness measurements in the field and laboratory, respectively. The need for developing enhanced methods for reliably characterizing the slip resistance properties is highlighted. This could be based on the principal understanding of the nature of shoe and floor interface and surface analysis techniques for characterizing both surfaces of shoe and floor. Therefore, surface roughness on both shoe and floor surfaces should be measured and combined to arrive at the final assessment of slipperiness. While controversies around the friction measurement for slipperiness assessment still remain, surface roughness measurement may provide an objective alternative to overcoming the limitations of friction measurements.
- [Show abstract] [Hide abstract] ABSTRACT: Surface roughness affects friction, so selection of floor surfaces with certain roughness characteristics could potentially reduce slip and fall accidents. This article summarizes the preferred surface microscopic geometric features that could increase friction on surfaces covered with liquid contaminants. Three types of surface features, represented by the average of the maximum height above the mean line in each cut-off length (R(pm)), the arithmetical average of surface slope (Delta(a)), and the kernel roughness depth (R(k)), are identified as preferred surface microscopic geometric features for a higher friction. The proper settings on the profilometers (instruments used to measure surface roughness) for optimizing these surface parameters are specified. The friction mechanisms involved reveal why these features are more desirable. Although surface roughness is important in determining slipperiness, there is still insufficient information to establish a safety criterion based on roughness; however, the method presented in this paper can readily provide a relative comparison. The summary presented will help safety professionals properly select new floor surfaces or assess existing floors to reduce slip and fall accidents.
- [Show abstract] [Hide abstract] ABSTRACT: In a companion paper (Development of a new analyzing model for quantifying pedestrian slip resistance characteristics: Part I. Theory and evaluation), a new tribology model capable of quantifying the surface interactions and wear evolutions between shoes and floors was presented. In the current paper, the model is used to analyze the surface interlocking mechanisms and wear developments between the shoe heels and floor surfaces by two groups of dynamic friction tests. The tests are conducted between three shoes and two different types of flooring specimens with similar range of roughness scales. The overall experimental results show that the comparative surface harmony was well correlated with the slip resistance results so that the calculated indices between each shoe and floor seem to be good estimators to predict the interfacial slip resistance properties. Several inter-related mechanisms such as material transfer and film formation were also found to be factors in the shoe-floor friction and wear phenomena. Three-dimensional microscopic observations clearly show that each shoe and flooring specimen had experienced various types of surface alterations and surface failures that were evolved throughout the entire tests. Wear patterns of each shoe depended on the particular combination of the shoe material and floor geometry. Overall wear modes of each flooring specimen show severe material transfers and film formations from an early stage of rubbings. From this experimental study, it becomes clear that the new measuring concept for the surface analysis shows a good correlation among the surface arguments, wear effects and slip resistance results. This agreement is encouraging for the search of a more reliable method than a simple friction measurement. Accounting for the effect of diverse walking conditions would be expected to improve the results.
- [Show abstract] [Hide abstract] ABSTRACT: Friction is widely used as an indicator of surface slipperiness in preventing accidents in slips and falls. Surface texture affects friction, but it is not clear which surface characteristics are better correlated with friction. Highly correlated surface characteristics could be used as potential interventions to prevent slip and fall accidents. The dynamic friction between quarry tiles and a commonly used sole testing material, Neolite, using three different mixtures of glycerol and water as contaminants at the interface was correlated with the surface parameters of the tile surfaces. The surface texture was quantified with various surface roughness and surface waviness parameters using three different cut-off lengths to filter the measured profiles for obtaining the profiles of either surface roughness or surface waviness. The correlation coefficients between the surface parameters and the measured friction were affected by the glycerol contents and cut-off lengths. Surface waviness parameters could potentially be better indicators of friction than commonly used surface roughness parameters, especially when they were measured with commonly used cut-off lengths or when the viscosity of the liquid contaminant was high.
- [Show abstract] [Hide abstract] ABSTRACT: Surface roughness affects friction, but it is not clear which surface roughness characteristics are better correlated with friction. The surface roughness parameters generated from quarry tiles were correlated with the transition friction between the tiles and a commonly used sole testing material, Neolite, with three different mixtures of glycerol and water as contaminants at the interface. Measurement of surface roughness usually requires removing the waviness portion from the measured profiles in order to focus on the surface features of interest through the selection of different cut-off lengths for filtering. The effect of cut-off length on the values of surface roughness parameters and their correlation with transition friction were investigated. The correlation coefficient between the surface roughness parameters and the measured friction was affected by the glycerol contents. The cut-off lengths of 2.5 and 8 mm resulted in stronger correlated surface roughness parameters than that of 0.8 mm. The surface parameters Δa, Rpm, Rk, R3z and Ra had a stronger correlation with the transition friction than other surface parameters examined in this study.
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