Probabilistic Modelling of Fatigue Behaviour of 51CrV4 Steel for Railway Parabolic Leaf Springs

The longevity of railway vehicles is an important factor in their mechanical and structural design. Fatigue is a major issue that affects the durability of railway components, and therefore, the knowledge of the fatigue resistance characteristics of critical components, such as leaf springs, must be extensively investigated. This research covers the fatigue resistance of chromium-vanadium alloy steel, usually designated as 51CrV4 from the high-cycle regime (HCF) (103 - 104) up to very high-cycle fatigue (VHCF) (109) under bending loading conditions, typical of leaf springs, and under uniaxial tension/compression loading, respectively, for a stress ratio of -1. Since different test frequencies were considered (23, 150, and 20 000 Hz), the frequency effect was also analysed, despite the material not exhibiting a significant frequency effect. In order to achive a new fatigue prediction model, two prediction models (the Basquin SN linear regression model and the Castillo-Fernandez-Cantelli (CFC) model were evaluated. According to the analysis carried out, the CFC model provided a better prediction for fatigue failures than the SN model, especially when outlier failure data are considered. The investigation also examined the failure modes, observing multiple cracks for higher loads and single cracks with initiation on the surface or from internal inclusions for lower loading. The present investigation aims to provide a fatigue resistance prediction model encompassing the HCF and VHCF fatigue region, for the fatigue design of railway wagon leaf springs or even for other components made of 51CrV4 with a tempered martensitic microstructure.