This paper describes a procedure for the determination of railway axle risk of fatigue failure under service loading for a simple fatigue assessment compliant to modern structural recommendations.\ud
After an initial review of reliability assessment under fatigue, a fully probabilistic approach is outlined, whose input data for the fatigue damage obtained with the EURAXLES project are briefly summarised. Then, a series of Montecarlo simulations was carried out in order to determine the maximum allowable stress for a given axle made of EA4T and EA1N under service conditions identified by di↵erent load spectra from the literature.\ud
Results have been obtained in terms of a safety factor for damage calculations that allows designers to adopt a simple semi-probabilistic approach for designing axles for a target reliability against fatigue. The application of this procedure to a railway axle then shows how safety factors should be have to be further increased for taking into the prospective presence of impact damages
The traditional experimental procedures used to generate thresholds (known as “ΔK-decreasing” and “constant Kmax”) have been challenged because it seems they affect the experimental results, sometimes in a non conservative way. In order to fix this problem, different experimental procedures (“compression pre-cracking constant amplitude” and “compression pre-cracking load reduction” (CPLR)) based on a compression-compression pre-cracking of fracture mechanics specimens have been proposed. Up till now, such procedures are not yet wide-spread between fracture mechanics experimentalists. In particular, due to the recent introduction, CPLR has been applied only to few cases: Al alloys, Ti alloys, and high strength steels (ultimate tensile strength>1300 MPa), all in the shape of M(T) or C(T) specimens subjected to positive stress ratios. The present paper deals with the application of these novel “compression pre-cracking” procedures, with particular attention to CPLR, to the unexplored and technically very important case of the structurally mild A1N steel grade (very commonly used to produce European railway axles) in the shape of SE(B) specimens subjected to stress ratios varying between −2 and 0.85.
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.
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