Since early 1860's rail vehicle axles are examined with regard to their structural durability. August Woehler was the first engineer who was working on this topic by means of cyclic loading which was evaluated to be a root cause for early in-service termination by fatigue phenomena. Different to static loads the effect of cyclic loading is time dependent: By every load cycle an incremental damage is created which may evolve to fatigue failure. Hence the huge number of load cycles within the life cycle of rail vehicles, which may for axles, will create operational incidents, or - even worse - fatigue cracks. Since it is proven that there is no endurance limit for engineered parts, the design validation process has to be reviewed for components which were created assuming an endurance limit and infinite life. The DT2.5/DT3 wheel set axles of Hamburger Hochbahn metro vehicles are such components which are currently running at >2.5 mio. km and will be used beyond 2012 having an annual mileage of more than 100,000 km. For one of those axles a fatigue crack at the area of the wheel press fit was monitored by regular ultrasonic inspection technology. Due to the unknown crack propagation rate for in-service loading the safety check by ultrasonic examination was reduced to an interval of 39,000 km, which created a major impact on costs and availability of these vehicles. Therefor the Hamburger Hochbahn AG organisation worked together with Fraunhofer LBF on a fail-safe concept which was developed on experimental crack growth data created by laboratory service load simulation of the DT2.5/DT3 axles.
Development of a fail-safe concept for metro vehicle axles by using crack growth results from service load simulation
2009
11 Seiten, 10 Bilder, 1 Tabelle, 4 Quellen
Conference paper
English
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