Fatigue assessment of railway axles is based on simple engineering approaches and uses allowable fatigue stresses taken from technical recommendations and standards. However these methods are unable to support the application of new high strength materials and of structural integrity techniques based on experiments on laboratory fatigue specimens. The scope of this paper is to investigate the scale effects in fatigue limit and in crack propagation rate of an 30NiCrMoV12 high strength steel with the aim of a better comprehension of fatigue properties of full-scale components. Firstly the 'scale effect' between fatigue limit of small specimens and full-scale axles relationship between crack size and fatigue limit were analyzed. For this purpose, a series of fatigue limit tests on micro-notched specimens subjected to rotating bending fatigue has been carried out. The results allowed to obtain the relationship between defect size and fatigue limit under rotating bending, the so-called 'Kitagawa diagram'. The fractographic analyses confirmed that fatigue limit of full-scale pieces is controlled by the presence of small non-metallic inclusions and these evidences have backed the definition of allowable design stresses and a new 'fatigue quality control' policy based on the estimation of maximum defects in a steel batch by using the statistics of extremes. To investigate the fatigue limit on press-fitted zone, a series of fatigue tests on special specimens has been carried out. These specimens had the central zone, with the characteristic wheel-seat shape, on which a little hub was press-fitted. The results of these tests and tests on full-scale components have shown no scale effect is present in fatigue limit on press-fitted zone. The growth rate of short cracks under rotating bending was analyzed too. The experimental results have then been used for formulating an EPFM crack growth model, which includes a 'mechanical threshold' dependent on the applied stress S. The model has been successfully compared with crack growth data from 'full-scale' tests on a new test rig for axle fatigue tests.
Full scale fatigue tests as a support to axle design
2003
10 Seiten, 11 Bilder, 18 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
Full scale fatigue tests as a support to axle design
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