Reciprocating sliding behaviour of human skin in vivo at lower number of cycles

Interfacial rub phenomena between human skin and other external surfaces is a prevalent problem in every day life. The improper skin friction would induce skin trauma. However, there are few publications on the friction mechanism of human skin and subsequent trauma to date. In this paper, the reciprocating friction testing of human volar forearm skin under different normal force and displacement amplitude have been performed. The normal force ranged from 0.1 to 12 N while the imposed displacement amplitude ranged from 2.5 to 17.5 mm. Tests lasting up to 1800 cycles with a frequency of 0.5 Hz were conducted. The tangential force (F-t) was recorded as a function of the displacement (D) during each cycle of the whole testing. The results showed that there were three kinds of F-t-D curve: the quasi-closed, elliptic and parallelepipedic cycle. A friction map comprising three friction regimes has been constituted according to the different kinds of F-t-D curve. The concept of friction sensation was introduced to qualitatively describe the pain, drag and heat of the tested skin at the different friction regimes. The most discomfort sensation has been obtained at the friction regime from sticking to gross relative sliding regime.