Rough surface rolling contact fatigue crack stress intensity factor calculation for modern rail steels

For premium grades (and rail surface treatments such as 'laser cladding') there is little plastic damage expected during typical operating conditions, and smooth surface contact models predict a long life. However, damage still develops, including rolling contact fatigue, affecting premium steels from multiple suppliers. A model is described predicting stress intensity factors and indicative crack growth rates for cracks driven by surface roughness stresses. Accompanying field data quantify the asperity separation and tip radii for rails from metro, mixed traffic and a freight line in ground or unground conditions. The results predict that in rough surface contact small surface cracks (50-100 mu m, exceeding microstructural dimensions) can grow faster than crack removal by wear, even when smooth surface models predict no growth. The model has application in identifying how rail grinding marks or wheel roughness may be an important factor in determining rail life through raised stresses at the rail surface (leading to wear), and increased stress intensities and growth rates for incipient cracks.