Multiple Crack Interaction with RCF Loading

Other conference contribution, 2008

Fracture and material degradation are of paramount importance for the life estimation of railway components. One particular class of fracture phenomena is associated with RCF (=rolling contact fatigue) in rails and wheels; a typical phenomenon is head checks which are pre-existing short surfacebreaking cracks in the rail with a spacing of about 2-3 mm. Since the crack spacing increases with the crack length, crack interaction becomes important. It turns out that such interaction results in either enhancement of the crack-driving force due to increased stresses or reduction of the crack-driving force due to crack shielding. The crack-driving force is defined in the context of “material forces”, which is a measure of the energy release rate due to a (virtual) variation of the position of the crack tip. In fact, it is a generalization of the classical J-integral (as known from linear elastic fracture mechanics). In this presentation we present 2-D FE simulations of the rolling contact problem using a in-house code written in FORTRAN 90. We discuss an idealized loading situation c.f. Figure 1. In view of all uncertainties it is challenging to carry out a numerical investigation of parameters that affect the crack interaction. The object of this investigation is to carry out a sensitivity study in order to obtain a better understanding of the "model". Parameters of interest is: initial crack angle, initial crack spacing, distribution of initial crack length, load contact zone in relation to spacing, FE mesh sensitivity, material properties (in particular the friction coefficient).