Experimental Study of the Effect of Humidity on Structural Changes of the “Third Body” during Friction

Friction is often accompanied by local fracture at the boundary of the contacting bodies. The gap between the bodies usually contains moving particles of different origin (“third body”), a change in the effective friction conditions may be associated with some changes in the structure of the third body. This paper presents a new series of experiments in which the process of rearrangement of intermediate layer particles interacting with various elastic materials (glass-rubber and steel) is modeled at different scale levels. A technique for visualizing the effect of mutual influence that occurs when two balls are pressed into a layer of rubber is proposed. It is the mutual influence that causes the effect of convergence or separation of the balls or particles during reciprocating frictional loading. The velocity of these processes depends on humidity and, in case of contact with the rubber layer, on the thickness of the layer. At high humidity, the configuration of the particles changes faster, and the friction force decreases. Replacing sand with an abrasive leads to an increase in the coefficient of friction and wear with a change in the microrelief of the surface. The minimum roughness is obtained for a humidity of 30%.