Experimental and theoretical investigation of the phenomenon of filling the RCF crack with liquid

In the contemporary models derived for rolling contact fatigue (RCF) crack stress analyses it is often assumed that liquid can penetrate crack interior if present on the contact interfaces. Several models of RCF cracks filled with liquid were built, which are based on this assumption. They account for the mechanisms of crack loading such as: mechanism of “reducing friction” inside the crack, “hydraulic pressure” exerted on the crack faces, “fluid entrapment” in the crack interior, or the “squeeze fluid film”. Additionally, it is assumed in most models, that liquid enters crack interior during the first part of loading cycle, in which crack faces undergo the phase of opening. At the present state of knowledge on RCF crack propagation in elements of bearings, gears and rails, possibility of the presence of liquid inside cracks and its significant role in mechanisms of their propagation is commonly accepted. But there are no until recently the appropriate model describing the way of liquid entering the crack. In the paper, the phenomenon of liquid entering the crack in the phase of crack opening during cyclic loading will be theoretically and experimentally investigated. The purpose of the experimental part of research is to monitor and measure the differences in the rate of crack propagation for dry and wet conditions. The tests are accompanied by the numerical analyses based on the precise FE model of a specimen and loading conditions.