Abstract
Rail transportation is a critical component of the modern transportation infrastructure. However, railroad rails are prone to various defects that can compromise their safety and reliability.
One of the most substantial risks to the safe operation of rail transportation involves the propagation of internal transverse rail defects, commonly referred to as detail fractures. Interestingly, these transverse fractures typically start from flat subsurface cracks that run parallel to the rail’s running surface and are usually referred to as “shell” defects. The shell defect is situated just a few millimeters below the surface of the rail crown.
It is hypothesized that transverse detail fatigue cracks form when a new vertical crack emerges from the existing shell crack and grows at a right angle to the original defect, eventually becoming a detail fracture. Detail fractures can grow to a critical size due to cyclic bending stresses in the rail, and this can result in catastrophic rail failures. Unfortunately, these fractures can reach a critical size without any noticeable damage on the visible outer surface of the rail.
Transverse detail fractures have been the subject of extensive research and attention within the rail industry for several decades. However, only a few studies have examined the origin of detail fractures and what causes these types of cracks to transition from initial shell defects.
In this paper, 3-D finite element crack growth simulations are used to model these distinctly different fracture geometries, to determine the role that “non-uniform” residual stresses, from the roller straightening process, may play in the transition from shell to detail crack. The modeling of crack propagation in 3-D, requires the computation of stress intensity factors around the entire crack front as the crack shape continuously changes. Under general, mixed mode, loading conditions, an initially planer crack, i.e., shell crack, will not remain in the plane, but will grow in a complex three-dimensional sense. Since the crack shape and direction continuously changes during the 3-D fatigue simulation, adaptive meshing must be employed for the accurate calculation of the stress intensity factors along the crack front.
The main results from this study should provide a better understanding of the mechanisms behind the transition from shell cracks to detail fractures in railroad rails and may be useful in the development of more effective inspection and maintenance practices for railroad operators, reducing the risk of unexpected failures and improving the safety and reliability of railroad systems.
