Evaluation of technical vs economic decisions in rail grinding
Rail is a significant capital asset for railway companies. It contributes more than half of the capital assets of railway infrastructure. Recent rail inspection data using Ultrasonic rail testing has shown increasing number of rail defects, failures and causing disruptions to rail services. This cost can be further increased when the track quality is poor. In recent years, railroads have been purchasing over 500,000 tons of rails per year at an estimated total cost of US $1.25 billion for replacement of worn out and degraded rails. Rail grinding is considered as viable means in reducing the impacts of rail defects and failures. Rail grinding can result in improved curving performance (wheel/rail interaction) and prevents crack initiation and propagation of surface cracks due to RCF. This paper focuses on analysis of rail degradation process and development of mathematical model considering technical and economic decisions in rail grinding to rail infrastructure owners.
MANAGING THE CRITICAL WHEEL/RAIL INTERFACE
In the UK, the Hatfield derailment in 2000 was caused by gauge corner cracking, which is a form of rolling contact fatigue. The cracking initiation and crack propagation processes that occur in rails as a result of contact between wheels and rails are described. Crack initiation and growth in rails depends on axle load, speed, cant, the quality of the rail surface, wheel roundness, track stiffness, and vehicle suspensions. A whole life model was developed by the University of Sheffield using data from AEAT Rail at Derby to predict and control the degradation processes occurring in the rail as a result of cyclic loading by the wheels.
Shear mode crack growth and rolling contact fatigue
Abstract Mixed mode crack growth direction criteria have been applied to calculations of the loading experienced by surface-initiated rolling contact fatigue cracks growing at a shallow angle to the surface. It was demonstrated that the cracks grow on the plane of the maximum shear stress rather than perpendicular to the maximum tangential stress as occurs during conventional fatigue testing. Mixed mode fatigue crack growth tests were then performed on rail steel specimens in an investigation of the effect of loading cracks in shear. It was demonstrated that while conventional mixed mode testing always produces cracks that either arrest after at most a millimetre of coplanar growth or branch to grow perpendicular to the tensile stress, under certain conditions similar to those experienced by rolling contact fatigue cracks, growth on the plane of the maximum shear stress range does occur. Additionally, under these conditions the cracks can grow up to 10 times faster than would be predicted by conventional fatigue testing.