Rubber friction: The contribution from the area of real contact

Abstract

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution F = τ A from the area of real contact A and a viscoelastic contribution F from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τ, for temperatures above the rubber glass transition temperature T, is weaker than that of the bulk viscoelastic modulus. The physical origin of τ for T > T is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < T, the shear stress τ is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Tactile perception of randomly rough surfaces

“…It is not a given that friction increases with rms curvature or equivalently with the micro-roughness at small scale. Roughness asperities may lower friction by reducing the real area of contact 34 – 36 or increase friction by dissipative deformation when sliding against a viscoelastic counter surface 37 – 39 like skin 40 , 41 or by elastic interaction with the skin micro-structure 42 . Here we found that friction increases with micro-roughness and that skin deformation by passing asperities causes additional friction.…”

Adhesion and Friction for Three Tire Tread Compounds

“…The concrete surface used in some of the experiments. The dark region arose from transfer of rubber material to the concrete surface during sliding at v = 1 mm s for two cycles (each cycle is 40 cm) at T = −40 ○ C. Reproduced from [9], with the permission of AIP Publishing, 2018.…”

“…Schematic picture of the low-temperature friction instrument allowing for linear reciprocal motion. Reproduced from[9], with the permission of AIP Publishing, 2018.…”

Design and development of a new portable test setup to study friction and wear

“…Friction in viscoelastic materials such as rubber occurs due to complex tribological processes and it has been extensively studied in the literature. [37][38][39][40][41][42][43][44][45][46] In a pioneer study on rubber friction, Grosch 38 found two main contributions to the friction, one from adhesion and the other due to viscoelastic energy dissipation in the rubber known as hysteresis friction. The contribution of adhesion is dominant at low sliding velocities, e.g.…”