Adhesive Rubber Friction

The behaviour and effects of the sliding friction exhibited by rubber is of key importance in industry. Whilst the effects of rubber friction can be empirically described the fundamental mechanisms behind the complex issue of rubber friction are still not well understood. This study will explore the adhesive friction displayed by various rubbers with differing levels of surface roughness over a range of sliding velocities. Conditions are maintained so as to produce pure sliding tests in order to exclude stress build up and release effects. The adhesive friction produced under these circumstances would be encompassed by the classical Schallamach theory; that of individual molecules forming weak bonds with the substrate, stretching and detaching in a cyclical manner. It is thought that this may not be the mechanism under which rubber adhesion occurs, a reason being that the molecules are likely to be too constrained in there structure to allow individual extension. This study supports through experimentation a model for the theoretical explanation of the displayed adhesive friction of a rough rubber surface sliding against a smooth surface. The model seeks to describe the behaviour of a solitary asperity as it peels off a rigid flat substrate. In doing so this model propagates fundamental relations from considerations of peel energy and fracture mechanics to give an equation for the expected frictional shear stress in terms of material properties, geometric quantities, and the sliding velocity. The validity of this model is analysed through the series of experiments that test the proposed theory. The experimental findings show a reproducible relation between the frictional shear stress and the velocity as predicted by the model. The results of both a sliding and rolling test also compare favourably to earlier data by Arnold et al. These findings give new insight in the field and present a basis with which to more accurately predict and assess the friction of polymeric components which could provide useful information in the process of design and manufacture.