Investigation of Skin Tribology and Its Effects on Coefficient of Friction and Other Tactile Attributes Involving Polymer Applications
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Perception and sense of touch are extremely important factors in design, but until recently, the exploration of skin tribology related to tactility has been relatively untouched. In this emergence, skin-on-polymer interactions are becoming more widely investigated due to the prevalence of polymers in everyday life, and the ability to define these interactions in terms of tactility would be hugely beneficial to the engineering and design process. Previous work has investigated polymer textiles concerning tactility, examining environmental and material properties that affect skin on fabric coefficient of friction. In this study, similar friction procedure was used to compare coefficients of friction of a fingerpad across varying polymer fabrics. Forces were applied in both longitudinal and lateral directions, and it was discovered that force directionality greatly affects coefficient of friction. Specific causes have yet to be determined, but it is suspected that material weave and microscopic surface properties play a major role in this directional behavior. To complement these studies and relate them to tactility, trained human evaluators rated the samples against four tactile attributes: abrasiveness, slipperiness, sensible texture, and fuzziness. These ballots were then analyzed with Quantitative Data Analysis and shown to be repeatable among the participants, and each of the attributes were shown to be statistically independent of coefficient of friction. It should be noted, however, that fuzziness showed the greatest correlation coefficient of R^2=0.27. Material selection plays an integral role in frictional behavior, and researchers have been studying contact theory on both microscopic and macroscopic levels to determine how surface topography affects skin-polymer tribology. To negate material effects discussed in the Greenwood-Williamson contact model, frictional tests were performed on identical polypropylene plaques with textured grooves of varying dimensions. Both geometry and directionality proved to be major frictional contributors; as groove size increased, finger friction in the longitudinal direction decreased, but friction increased laterally. In addition to testing a fingerpad, friction was measured with a silicone wand to simulate a finger with different material properties. The silicone exhibited the opposite trend as skin; as groove width decreased, frictional forces increased longitudinally and decreased laterally. While topography affects frictional behavior, counterface stiffness, and intrinsic material properties may cause the trend shift between skin and silicone.
Darden, Matthew Aguirre (2010). Investigation of Skin Tribology and Its Effects on Coefficient of Friction and Other Tactile Attributes Involving Polymer Applications. Master's thesis, Texas A&M University. Available electronically from