Visualization and Modelling to Understand Rail Rolling Contact Fatigue Cracks in Three Dimensions

Abstract

The paper presents an extensive survey of experimental data on rolling contact fatigue (RCF) crack shape and propagation characteristics in rails removed from service, where such cracks are angled to the rail axis. The data includes re-analysis of previously published experimental data to extract crack shape information and new experimental work on crack shapes at different stages in the early RCF life. Periods from initiation (ratcheted 'flake cracks') have been considered through very early growth to the limit of one prior austenite (PA) grain and on to rail-head visual cracks. Techniques included multi-sectioning through single cracks and crack zones, on used rail and test discs, to build up real 3D data on crack shapes and propagation characteristics. This data has been compared with the UK rail system guidance charts relating to visual crack length and respective vertical depth; all data fell within the indicated guidance zones. The configuration of such angled cracks, typically found in curves, so aligned due to the vector of both lateral and longitudinal traction, rather than just axially, was identified as an important case for modelling. A fracture mechanics based model has been developed to predict mode I and II stress intensity factors for such cracks covering multiple PA grains. An important geometry effect is revealed by which a contact approaching a crack angled to the rail axis is effectively 'offset' from the approach direction considered in 2D models, thereby resulting in lower predicted peak stress intensity factor values, compared with 2D, for the prediction of crack growth rates.

Interaction between cracks and microstructure in three dimensions for rolling contact fatigue in railway rails

“…They are rather elongated as compared with the field sample where the crack shape can be considered semicircular, see Fig. , and resembles a crack investigated in a comparable rail by Garnham et al . The crack surfaces are smoother for the test rig sample as compared with the field sample where the cracks have more asperities, see Fig.…”

“…However, few attempts have been made to show cracks in railway rails in three dimensions. Garnham et al . made an attempt by cutting a used rail with cracks into six slices.…”

Long co-planar mode III fatigue crack growth under non-proportional mixed mode loading in rail steel

“…In Figure 15, although the variance is relative large, almost the same growth rates are obtained which implies that when co-planar growth assisted by mode I occurs, the growth rates are about the same regardless of whether the main driving force is in-plane shear or out-of-plane shear. Garnham et al 19 improved the two-and-a-half dimensional stress intensity factor calculation method to investigate the effect of lateral traction. This modelling approach uses 3D stress field and two-dimensional Greens functions; therefore, it can predict K I and K II but not K III .…”

Prediction of rail damage using a combination of Shakedown Map and wheel-rail contact energy

“…rail grinding). Due to the effect of several factors and changing contact conditions experienced by rails in different operating environments, the previous investigations revealed no direct correlation between surface length and crack depth [26,27].…”