Railway wheel tread damage and axle bending stress – Instrumented wheelset measurements and numerical simulations

A combination of instrumented wheelset measurements and numerical simulations of axle bending stresses is used to investigate the consequences of evolving rolling contact fatigue (RCF) damage on a passenger train wheelset. In a field test campaign, stresses have been monitored using a wheelset with four strain gauges mounted on the axle, while the evolution of wheel tread damage (out-of-roundness) has been measured on regular occasions. The strain signals are post-processed in real time and stress variations are computed. Based on a convolution integral approach, the measured wheel out-of-roundness has been used as input to numerical simulations of vertical dynamic wheelset–track interaction and axle stresses. Simulated and measured axle stresses are compared for cases involving combinations of low or high levels of rail roughness and the measured levels of RCF damage. The study enhances the understanding of how wheel tread damage and track quality influence axle stress amplitudes

An investigation about the influence of deep rolling on fatigue crack growth in railway axles made of a medium strength steel

Over the last years, deep rolling has been adopted to improve the fatigue strength of railway axles, but very few scientific analyses and studies of this phenomenon are available in the literature. For this reason, the present research investigates some aspects related to the influence of this technological process on fatigue crack growth in railway axles made of EA4T steel grade. Firstly, special full-scale specimens were prepared applying the industrial deep-rolling process. The measurement of the resulting compressive residual stress field was then performed by x-ray diffraction and prompted an experimental crack growth campaign, on small-scale SE(B) and SE(T) specimens, to investigate the behavior of the material at very negative stress ratios. Crack growth tests were then carried out on full-scale specimens and the results successfully compared to those obtained by a simple no interaction predictive model built up considering both the characterized behavior of the material and the measured residual stress field

Load Interaction Effects in a Medium Strength Steel for Railway Axles

As is well known, an interaction effect arises on crack propagation when a specimen or a component is subjected to variable amplitude fatigue loading. Depending on the applied load sequence, a certain amount of retardation or acceleration can then be observed, on the fatigue crack growth rate, with respect to the constant amplitude case. In the case of structural ductile materials, the interaction phenomenon is mainly addressed by the local plasticity at the crack tip and can be explained, from a global point of view, by adopting the crack closure concept. From this point of view, in the present research, load interaction effects in a medium strength steel for railway axles are analyzed. An experimental campaign was carried on this material, using SE(T) specimens, in order to understand and quantify the interaction effects arising from relevant load sequences derived from service. The experimental outcomes were then modeled adopting both a simple no-interaction approach and a more sophisticated strip-yield model in order to quantify the possible interaction effects. The modeling was carried out considering different experimental techniques for deriving the crack growth and threshold behaviors of the material, i.e., the traditional DK-decreasing technique and the compression pre-cracking one

Investigation of Fatigue Crack Growth in Full-Scale Railway Axles Subjected to Service Load Spectra: Experiments and Predictive Models

In this paper, a series of experimental investigations was performed on full-scale railway axles to analyze the fatigue crack growth behavior of EA4T steel under load spectrum derived from real operating conditions. The experimental results were compared to life predictions carried out adopting two models: (i) the conventional Nasgro equation and (ii) the cyclic R-curve concept implemented in the Modified Nasgro equation for describing the crack growth behavior of an arbitrary crack length. The results show that the life predictions performed by means of the Modified Nasgro equation coincide well with the experimental results with an underestimation of the residual lifetime less than 32%, while the traditional Nasgro equation leads to significant overestimation (≈120%) of the residual lifetime for load spectra close to the in service scenario

Crack Growth Studies in Railway Axles under Corrosion Fatigue: Full-scale Experiments and Model Validation

Crack initiation and growth in full scale railway axle in A1T mild steel have been studied, under three points rotating bending loading conditions and artificial rainwater as corrosive environment. A surface plastic replication technique has been used along with optical microscopy and Scanning Electron Microscopy to monitor the environment assisted fatigue at various stages. A modified Murtaza and Akid empirical model has been employed to predict the corrosion fatigue crack growth rates and a reasonable agreement has been found between experimental and calculated lifetime

Prediction of axle fatigue life based on field measurements

To facilitate the adoption of a condition-based maintenance approach for railway axles, more knowledge regarding operational loading is needed. In the present work, statistical distributions on axle stresses for revenue vehicles have been derived. To this end, raw strain spectra have been gathered during field measurements using an instrumented telemetry mounted on a powered axle running within the Swedish railway network. Strain spectra are transformed into bending stress spectra which are used to estimate the statistical distributions of axle stresses for different track sections. Both the derived stress spectra and the estimated statistical distributions are used as input to fatigue life analyses. In these analyses, W\uf6hler (stress–cycle) curves estimated for varying axle surface conditions (which can be related to different axle maintenance conditions) are used to predict axle lives. The proposed method allows to rapidly post-process data obtained during field tests, to quantify indications on the health status of track and of the wheelset from these, and to estimate resulting fatigue life. This would aid in asset management by enhanced status characterisation, improved inspection and maintenance planning, and enhanced possibilities to follow-up any non-conformities