Friction and deformation behaviour of human skin

Abstract

The skin friction and deformation behaviour both in-plane and perpendicular to the sliding direction have been measured simultaneously during in vivo reciprocating-sliding of a smooth steel ball probe against human forearm skin. In these experiments, the skin is compressed in front of the probe, forming a “bow-wave”, and stretched behind as a consequence of friction and lateral skin displacement. The effects of two probe diameters and two normal loads on the skin friction and deformation behaviours were investigated for nominally dry skin in a 22 °C, 50% relative humidity environment. Friction force “stick” and “slip” phases could be distinguished during the probe motion cycle and these could be related to the skin deformation behaviour, allowing the effective lateral skin stiffness to be estimated for the different experimental conditions. Comparison to measurements of the effective indentation stiffness of the skin showed differences in the effects of load and probe diameter that may be attributable to differences in the extent of the deformation field within the skin and the complex structure and anisotropic mechanical properties of the different skin layers. The different friction results observed for different loads and probe diameters could be interpreted using an adhesion friction model for smooth contact with hydrated skin, taking into account the skin effective elastic modulus. For the experimental conditions applied here, deformation friction appeared to play only a minor role in determining the total skin friction force.