[SY-O1] Symposium O-1

[SY-O1] The adhesive behavior of elastic contacts in the presence of interfacial shear stresses

Nicola Menga^1,2, ^○Giuseppe Carbone^1,2, Daniele Dini² (1.Department of Mechanics, Mathematics and Management - Polytechnic University of Bari, Italy, 2.Department of Mechanical Engineering, Imperial College London, UK)

Among the many factors influencing the contact behavior of two mating surfaces, the interplay between shear stresses (and associated frictional response) and adhesion in elastic contacts is still a long-standing tribological problem. Most of the theoretical models focusing on this phenomenon seem to indicate that the presence of frictional stresses at the sliding interface tend to mask adhesion, thus leading to a reduction of the contact area. This is usually explained by invoking the only theory available in the literature (by Savkoor and Briggs in 1977) to study the interrelation between contact tangential stresses and adhesion, which, however, holds true only in the case of full stick conditions between the mating surfaces, i.e. when slip at the contact interface is totally prevented from taking place. Moreover, on the contrary, some experimental investigations have shown that, under gross slip conditions between almost perfectly smooth surfaces no contact area reduction is observed as long as the sliding velocity is moderate, and in some cases, even an increase of the contact size is reported. Aiming at shedding light on this behaviour, we focus on the adhesive sliding contact between two perfectly smooth surfaces under the condition that gross slip takes place at moderate velocities. We treat the exemplar case of a smooth rigid sphere sliding on a soft elastic half-space. We developed a theoretical model, which, by relying on the theory of contact mechanics and on arguments borrowed from thermodynamics, shows that an increase of the contact area, compared to the classical JKR case, may be caused by the presence of constant uniform shear stress at the interface. This is specifically true at low velocity, before the onset of stick-slip. In fact, at low-speed sliding, the shear stress fluctuations at the interface, which produce an apparent repulsive surface energy term, are negligible compared to the average stress. However, when the contact moves into the stick-slip regime the shear stress fluctuations may become comparable to the average interfacial stress leading to a strong repulsive surface energy, which may also justify why adhesion is instead almost completely masked at relatively large sliding velocities.