Rolling contact problem – fatigue crack propagation in a surface layer

The paper deals with the problem of development of fatigue cracks in a surface layer, which is at present one of the most actual issues of contact mechanics. The results obtained by the authors from experimental and numerical investigations of the factors, which exert an essential influence on the propagation process of a crack of the "squat" type in the wheel/rail contact zone are presented.

In the first part of the work, the results obtained using the Immersion Method of Holographic Interferometry from the investigation into the shapes of faces of the cracks detected in rail heads are presented. Furthermore the experimental investigations into crack faces interactions conducted on the samples made of 900A steel under complex loads obtained by means of the Grating Holographic Interferometry are presented as well.

In the second part of the paper, the results of numerical investigations into 3D cracks of the "squat" type are discussed, with a complex stress state in the contact zone, stresses due to rail bending, residual stresses as well as thermal stresses taken into account. The investigations of the effect of conditions of crack faces interaction on simulation results, which have been conducted using 2D models are presented as well. Eight different cases were considered, and the results having the form of Stress Intensity Factor $\;K_{II}$ courses versus the load position relative to the crack are presented.

In the last part of the work the results of numerical simulations of rolling the wheel over the raceway with an oblique crack are presented. The conditions of crack faces interaction used in simulations were determined, basing on the experimental investigations.