3D model of liquid entrapment mechanism for rolling contact fatigue cracks in rails

Abstract

In the paper, the iterative numerical procedure was used for estimating the 3D crack front loading enhancements due to the action of the “liquid entrapment mechanism” (LEM). The 3D shallow angle, semi-elliptical, surface breaking crack inclined at 20° to the horizontal, in an early stage of development (similar to the “squat”-type crack typical in rails) was FE modelled and used for analysis. The volume of liquid entrapped was determined on the basis of the 3D crack geometry for the position of load, in which the leading edge of contact patch is touching the crack mouth. In the FE model this volume was represented by the empty space (bubble) between the crack faces loaded with the liquid pressure. During the LEM part of the cycle of loading this volume was assumed to be constant. At each position of contact load (rolling wheel), the pressure was gradually increasing in the iteration procedure until both the required volume of the “bubble” and “equilibrium state” with external contact load were attained. Then, the histories of Modes I, II, and III stress intensity factors (SIFs) and corresponding fatigue growth rates were determined for the selected points of the crack front. The obtained loading enhancements were compared with those estimated earlier by the authors and others on the basis of the 2D model of LEM.