Human hands sweat in different circumstances and the presence of sweat can alter the friction between the hand and contacting surface. It is therefore important to understand how hand moisture varies between people, during different activities and the effect of this on friction.In this study a survey of fingertip moisture was done. Friction tests were then carried out to investigate the effect of moisture.Moisture was added to the surface of the finger, the finger was soaked in water, and water was added to the counter-surface; the friction of the contact was then measured. It was found that the friction increased, up until a certain level of moisture and then decreased. The increase in friction has previously been explained by viscous shearing, water absorption and capillary adhesion. The results from the experiments enabled the mechanisms to be investigated analytically. This study found that water absorption is the principle mechanism responsible for the increase in friction, followed by capillary adhesion, although it was not conclusively proved that this contributes significantly. Both these mechanisms increase friction by increasing the area of contact and therefore adhesion. Viscous shearing in the liquid bridges has negligible effect. There are, however, many limitations in the modelling that need further exploration.

No abstract

Background/Purpose: The work outlined in this paper was aimed at achieving further

This paper describes three series of tests that were designed to investigate how skin mechanical and structural properties, measured using a "Cutometer" and Optical Coherence Tomography, affect the frictional behaviour of human finger-pads. Firstly, the skin mechanical properties across all fingers and the palm in participants' dominant hands were assessed. Results showed that the distensibility of skin (total deformation in a suction test) is associated with stratum corneum thickness and that this in turn affects friction (thicker stratuem corneum leads to higher friction), giving a link between distensibility and friction.Tape stripping to remove the superficial layer of the skin led to increased moisture (and/or electric charge on the skin surface) led to higher friction. No accompanying changes were seen in structural properties so it was concluded that moisture was the main cause of the adhesion increase. More work is required to isolate moisture and possible changes in electric charge using alternative measurement techniques.When rubbing with sand paper, the stratum corneum thinned considerably and friction reduced. Moisture was ruled out as a cause of friction changes in this instance. Skin normal stiffness also did not change, but lateral stiffness changes have been seen in previous work when the stratum corneum thickness has been reduced so this is likely to be the cause of the reduced friction. This will be investigated further in future work using dynamic OCT measurements.

No abstract