How to Predict Rail Dynamics to Prevent System Failures – Rails with a Splice Bar

The understanding of different dynamic phenomena is essential to prevent failure in any dynamic structural system. It is especially vital when dealing with transport systems, where failure is not permissible. Subsequently, for rail systems, Vibratec has developed high level skills and experience in modelling the wheel/railway contact using non-linear simulation through MSC.Marc software.

A complete system can be modelled, including the wheel and its axle; the railway with the sleepers; the pads; and the ballast. All mechanical parameters can be tuned according to Vibratec’s large database (built over many years of experience in the railway industry with the major clients in this domain). A compromise has been found between the accuracy of the results and the computational time (which can be prohibiting without particular care in case of complex non-linear simulations). The wheel can also be treated in translation and in rotation.

Using these accurate and efficient models, any flaw in the rail system can be considered and correlated to the dynamic load seen by the axle and the railway. In this instance rails joined with a splice bar, though it is also possible to consider gaps; missing sleepers; change of ground properties etc. Using this methodology creates a powerful tool with which to predict critical excitation of the railway which in turn could, dramatically, lead to failure. Moreover, specific modeling details such as the pre-load on the screws holding the splice bar with the rails are completely controlled.

In this instance the study related here concerned rails joined with a splice bar. The Hertz contact was correctly determined, and the dynamic load fluctuations were correlated to the gap between the rails, the wheel speed and the system {wheel+axle} dynamic behavior. Indeed, a complete approach using an MSC.Marc simulation was achieved.  The simulation was coupled with additional investigations of a modal basis computation, plus parametric excitation due to the railway stiffness variations according to longitudinal coordinates. This approach allowed Vibratec to acheive a truly global understanding of the system dynamics.

This knowledge ensured that Vibratec was able to make specific practical recommendations for design changes and remedial actions to prevent, or minimise the likelihood of failures occurring.

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