Recent evaluations of the causes of axle failures during service have shown that the so-called 'endurance limit design' approach adopted to date does not fully consider the conditions experienced in actual operational use. In the present European Standards used for the design of axles (EN 13,103 and 13,104), the maximum design stresses are calculated using specific load factors for traversing curves. The allowable stresses are based on the fatigue strength at 107 cycles. Neither of these standards satisfies the requirements concerning the required service life of axles. For an axle of an ICE train with a wheel diameter of 0.9 m and a travelled distance of 500,000 km per year a total of 484,000 axle revolutions or cycles are generated each day of usage; therefore, 107 cycles are achieved in about 21 days of operation. This high number of cycles leads to a continuous decrease of the fatigue strength. An analysis of observed cracks on modern trains has resulted in the conclusion that a structural endurance limit does not exist and thus the reliable approach used to validate the structural durability must be based on a finite durability life that takes into account the structural fatigue properties under real usage conditions. It is highly important that this knowledge, as the state of the art, is applied for structural durability validation and also included in taught courses as well as in specific standards. The following statements summarize the state of the art in this area. 1. An optimal as well as reliable design of wheelset axles must take into account the operational stress spectra (or axle loads) and the fatigue strength of axles. An appropriate procedure must ensure that these decisive factors are adequately considered. 2. The estimation of the expected fatigue life must include statistical aspects of the scatter of the components fatigue strength. 3. In the design stage, the fatigue strength validation and resulting dimensioning should be based on the appropriate loading and fatigue strength data, including specific safety factors for the required design life. The allowable (permissible) stress, represented by S(a,eq for N = 107 cycles depends on the fatigue strength in an individual axle area as well as on the design spectrum for the required service life. 4. For the inspection of axles, it is necessary to improve the numerical procedures used to estimate the crack propagation and verify them both by experimental investigations and by practical experience. 5. A reliable approval of axle durability, especially in the case of new materials, manufacturing technology and train types, should include an experimental validation in the existing durability test facilities taking into account the service stress spectra as is current practice in the car and aircraft industries.
Railway axle failures and durability validation
2012
12 Seiten, 10 Bilder, 1 Tabelle, 14 Quellen
Article (Journal)
English
Railway axle failures and durability validation
SAGE Publications | 2012
|Railway axle failures and durability validation
Online Contents | 2012
|Engineering Index Backfile | 1941