Static Friction Coefficients. The friction coefficients considered below are for static friction cases where two solid surfaces in contact with each other are resisting relative lateral motion. It should be noted that there can be significant differences between static friction (typically higher) and kinetic (sliding) friction. F ult = ultimate skin friction; α = skin friction coefficient obtained using the correlations provided by Kolk and Van der Velde. Α is a parameter based on both cohesion and effective stress; S u, undrained shear strength (cohesion). “α” in the Kolk and Van der Velde equation is based on the ratio of undrained shear strength.
The skin friction coefficient represents the skin resistance against the movement of an object on the skin surface. The coefficient of friction (μ) is calculated as the ratio of the friction force over the normal load. The normal load and friction force are expressed in newtons (N), and the coefficient of friction is dimensionless μ = Ffriction/Fnormal (Naz et al. 2014). Many devices, including a triaxial quartz force plate (Kistler, Winterthur, Switzerland) (Derler et al. 2007; Gerhardt et al. 2008), Revolt SkinTribometer (Veijgen et al. 2013a, b), Frictiometer® FR 770 (Courage-Khazaka, Cologne, Germany) (Zhu et al. 2011; Neto et al. 2013), and Measurement Technologies Skin Friction Meter (Aca-Derm Inc., California, USA) (Zhang and Mak 1999), are available for the measurement of skin friction coefficients. The principle and methods of these devices are similar. For Courage-Khazaka Frictiometer® FR 770, the flat tip of the probe is made of Teflon. The tip surface area contacting the skin is 2 cm2. The normal force level is 0.7 N and rotation speed is 255RPM. During measurement, the Frictiometer® FR 770 probe is connected to an MPA5 unit which is linked to a computer. The skin friction coefficient will be displayed on a computer monitor upon placing the probe on the surface of the skin. The unit for skin friction coefficient is arbitrary unit (au).
The skin friction coefficient represents the skin resistance against the movement of an object on the skin surface. The coefficient of friction (μ) is calculated as the ratio of the friction force over the normal load. The normal load and friction force are expressed in newtons (N), and the coefficient of friction is dimensionless μ = Ffriction/Fnormal (Naz et al. 2014). Many devices, including a triaxial quartz force plate (Kistler, Winterthur, Switzerland) (Derler et al. 2007; Gerhardt et al. 2008), Revolt SkinTribometer (Veijgen et al. 2013a, b), Frictiometer® FR 770 (Courage-Khazaka, Cologne, Germany) (Zhu et al. 2011; Neto et al. 2013), and Measurement Technologies Skin Friction Meter (Aca-Derm Inc., California, USA) (Zhang and Mak 1999), are available for the measurement of skin friction coefficients. The principle and methods of these devices are similar. For Courage-Khazaka Frictiometer® FR 770, the flat tip of the probe is made of Teflon. The tip surface area contacting the skin is 2 cm2. The normal force level is 0.7 N and rotation speed is 255RPM. During measurement, the Frictiometer® FR 770 probe is connected to an MPA5 unit which is linked to a computer. The skin friction coefficient will be displayed on a computer monitor upon placing the probe on the surface of the skin. The unit for skin friction coefficient is arbitrary unit (au).