The management of fatigue crack growth in railway axles

Abstract

Railway axles are safety-critical components. Designing failsafe mechanisms is very difficult and the safety of the component is determined though a good understanding of the structural integrity and through effective management policies. This article first reviews from a historical viewpoint the development of the design and management of railway axles and then outlines state-of-the-art methodologies to be employed in the successful management of railway axles. Advancements in fatigue fracture mechanics have permitted the development of statistical techniques that enhance the understanding of axle failures which occur relatively infrequently. Because of the extremely low number of in-service failures, there exists a possibility to modify the non-destructive testing (NDT) inspection regime. This will reduce the maintenance costs without compromising safety. It is also shown that the probability of failure of an axle is profoundly influenced by the probability of missing a large fatigue crack during an NDT inspection. This crack may be growing rapidly and failure will ensue before the next inspection. The sensitivity of NDT techniques to small cracks is less important since these cracks will be growing relatively slowly and are not a threat to the structural integrity of the axle.