Abstract
Tactile perception and friction can be modified by producing a deterministic surface topography. Change of surface feature arrangement and texture symmetry can produce an anisotropic frictional behaviour. It is generally achieved through skin hysteresis by promoting its deformation. This work investigates whether a bidirectional friction can be created with microscale ellipsoidal asperity textures, thus relying on the adhesive component of friction. For this purpose, four textured samples with various asperity dimensions were moulded with a silicone rubber having an elastic modulus comparable to that of the skin. Coefficient of friction measurements were conducted in-vivo in two sliding directions with a range of normal loads up to 4 N. Finite element method (FEM) was used to study elastic deformation effects, explain the observed friction difference, and predict surface material influence. Measurements performed perpendicular to the asperity major radii showed consistently higher friction coefficients than that during parallel sliding. For the larger asperity dimensions, a change of the sliding direction increased friction up to a factor of 2. The numerical analysis showed that this effect is mostly related to elastic asperity deflection. Bidirectional friction differences can be further controlled by asperity dimensions, spacing, and material properties.
Highlights
People interact through touch with numerous objects and rely on perceived surface properties in everyday tasks
The reference sample tested during the first measurement series showed considerably lower friction coefficient
Reduction of the friction coefficient with increase of roughness is consistent with literature [10, 16, 17, 19]
Summary
People interact through touch with numerous objects and rely on perceived surface properties in everyday tasks. An individual’s judgement of a surface is commonly described by four perceptual scales: hardness, warmth, roughness, and stickiness [1, 2]. The latter three are directly related to surface topography and, can be engineered through surface design. The relationship between tribological mechanisms and touch perception is not fully understood. There are reported correlations between surface roughness and perceived coarseness [3], as well as between calculated friction coefficients and stickiness [4]. The textures with micro-scale features and spacing below 160 μm have shown the lowest friction but were uniformly categorized by volunteers as smooth and most likeable
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