Damage Tolerance of Rail Vehicle Energy Absorbers

Despite significant progress in the design of rail vehicles to ensure a high level of passive safety the effects of quality of manufacturing and assembly parameters on the local and global structural behavior in the event of a collision have not been adequately addressed. The present paper deals with one of these aspects, namely the attachment of impact energy absorbers at the front end of rail vehicles, since the functional requirements of these devices are particularly stringent in terms of their reliability and functionality throughout the life of the vehicle. In this work the merits of a welded and a bolted energy absorber design are investigated, the latter offering the advantage of ease of through life maintenance and replacement, ensuring that defects such as general corrosion or cracks that could have affected their performance are easily identified and replacements made and also introduce the prospect of retrofitting energy absorbing devices to older rail vehicles to improve crashworthiness. FEA modelling to simulate the dynamic response of welded and bolted joints has been carried out using the LS-DYNA code. For the welded joints the influence of welding defects such as lack of fusion, weld under matching, and weld cracking on the performance of the energy absorbers has been investigated. The numerical model, validated on the basis of results from impact tests, was subsequently used to investigate the behaviour of the absorption system in collision scenarios as prescribed by EN 15227:2008Peer reviewe

Assessment of Fatigue Cracks in Rails

The fatigue behaviour of cracks at the foot region of a rail subjected to bending load has been investigated. Depending on the position of initiation of a small semi-elliptical surface crack in a rail, the crack front changes shape during propagation to failure due to the large variation of the stress intensity factor from point to point round the crack front due to differences in the local stress field as each point round the crack front lies at different distances from the neutral axis of the rail. This condition implies a variable crack growth rate that transforms the crack front shape during fatigue crack propagation. SIF values have been estimated by means of both the finite element method and analytical solutions derived for a semi-elliptical crack in a finite rectangular cross-section beam. The SIF value predictions obtained with the two methods show good agreement suggesting that the analytical solutions can be used for a rapid assessment of the severity of a flaw in a rail. A predictive model for crack growth has been derived for an initial small crack at an initiation point at the foot/web corner of a rail tested under four point bending fatigue in the laboratory, showing a reasonably good prediction of both the shape and size of the crack at failure when compared with experimentPeer reviewe