5.1 Spalling associated with RCF
When RCF is initiated at the rail surface e.g. GCC, cracks can develop several millimetres into the rail if a fluid such as water or a lubricant is present. When cracks reach a depth that is approximately that of the so-called “compressive residual stresses” (typically about 5mm), they tend to go in one direction or another i.e. they “branch”.
If a crack branches approximately parallel to the rail surface, it tends to meet up with another crack to form a spall. The crack is then no longer active and the spall is sometimes worn away by traffic.
The conditions in which a crack branches parallel to the rail surface and those in which it branches down into the rail (potentially to form a transverse defect) are not yet fully understood.
There is some evidence that grease exacerbates spalling.