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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.

This paper outlines work carried out to produce maps of rail material wear coefficients taken from laboratory tests run on twin disc and pin-on-disc machines as well as those derived from measurements taken in the field. Wear regimes and transitions are identified using the maps and defined in terms of slip and contact pressure. Wear regimes are related to expected wheel/rail contact conditions and contact points (rail head/wheel tread and rail gauge/wheel flange). Surface morphologies are discussed and comparisons are made between field and laboratory data.

Loss of adhesion between a railway wheel and the track has implications for both braking and traction. Poor adhesion in braking is a safety issue as it leads to extended stopping distances.In traction it is a performance issue as it may lead to reduced acceleration which could cause delays.In this work wheel/rail adhesion was assessed using a twin disc simulation. The effects of a number of contaminants, such as oil, dry and wet leaves and sand were investigated. These have been shown in the past to have significant effect on adhesion, but this has not been well quantified.The results have shown that both oil and water reduce adhesion from the dry condition.Leaves, however, gave the lowest adhesion values, even when dry. The addition of sand, commonly used as a friction enhancer, to leaves, brought adhesion levels back to the levels without leaves present. Adhesion levels recorded, particularly for the wet, dry and oil conditions are in the range seen in field measurements.Relatively severe disc surface damage and subsurface deformation was seen after the addition of sand. Leaves were also seen to cause indents in the disc surfaces.The twin disc approach has been shown to provide a good approach for comparing adhesion levels under a range of wheel/rail contact conditions, with and without contaminants.

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Leaf-related adhesion problems have been present in many railway networks all over the world in the last few decades. Since the early 1970s many measures have been undertaken in order to mitigate the problem. One of the measures adopted by many railway networks is the use of friction modifiers. However, the low adhesion problem still persists. Furthermore, the effectiveness of these friction modifiers has not well proven yet due to the lack of research in controlled conditions. Consequently, the rolling stock operators and infrastructure managers do not clearly understand the performance and side effects of the friction modifiers used on their networks. In this paper, an investigation of the performance of two existent friction modifiers in controlled laboratory conditions is presented. These friction modifiers have been used or tested in several railway networks. A twin-disk roller rig has been used to study their performance in leaf contaminated contacts. The adhesion characteristics of both friction modifiers are examined for different slip ratios. The constituents of the friction modifiers are identified and the solid components are analyzed. In addition, damage that these friction modifiers may cause to wheel and rail is also discussed.

Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45-50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40-50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching.