Analysis of internal cracks in railway wheels under experimentally determined pressure distributions

In recent years much effort has been devoted to the definition of design approaches of railway systems based on the analysis of the system itself and on accurate knowledge of its effective working conditions. In this paper, the attention is focused on railway wheels. This latter component is subjected to different types of damage: sub-surface crack propagation is considered. The prediction of the evolution of this process depends on the knowledge of the stress intensity factors concerning modes I, II and III, which are dependant both on the total load acting on the wheel and on how the load is transmitted through the wheel/rail interface. However, until now the solutions commonly used consider a theoretical (Hertzian) pressure distribution, even if, due to wear or to the dynamic phenomena, the actual contact patch can be strongly different for most of the lifespan of the wheel. An approach is developed with the aim to solve the case of an internally cracked wheel subjected to an arbitrary contact patch and pressure distribution. It is based on Boussinesq's formulae and utilises a three-dimensional finite element model of the part of the wheel close to the crack to calculate the stress intensity factors along a curvilinear crack front. Pressure distributions experimentally determined by means of a technique based on the reflection of high-frequency ultrasonic waves from the wheel–rail interface were applied to internal cracks in wheels: the results were critically compared with the those obtained by considering Hertzian pressure distributions, the aim being the assessment of the influence of the contact conditions in respect of damage cause by internal crack propagation.