RIS ID
129781
Abstract
A railway turnout, switch or set of points is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction, or where a spur or siding branches off. The turnout consists of the pair of linked tapering rails, known as points, lying between the diverging outer rails. A section of New South Wales' railways rail turnout was removed, since testing revealed that it had become defective and no longer fit-for-purpose. University of Wollongong was commissioned to investigate the failure mode(s) of the track section, and to provide a detailed report on the material composition, heat treatment, surface finish, wear and any material defects. since the turnout is over 25 years old, there are no test certificates or other quality assurance documents available for review. A literature search into turnout construction methods has shown that the Australian Standard AS 1085.21:2014 'Railway Track Material - Turnouts, Switches and Crossings' specifies that the turnout be made from cast high manganese steel. Manganese steel has the propensity to work harden rapidly over time. The turnout section of railway track was first cleaned and prepared for sampling. The head of the beam was cleaned with 'Penetrene' fluid and 'Scotch Bright' type scourers, until the rust and grime had been stripped back to reveal the clean metal below. The surface was then inspected for wear, damage and any adverse anomalies associated with the manufacturing process. Once inspected, the rail section was marked out for the cutting of samples. Samples were taken from strategic places along the beam including the head, web and in the convergence where the fracture was observed. Sample material was extracted from the turnout using the water jet cutting process. These samples were then prepared for metallographic microscopy, where inspections of the damaged areas were conducted and an assessment made to determine the cause of failure. Two different modes of failure were observed, namely: work hardening of the top face of the rail head resulting in spallation of the surface finish; high stress concentration from loading in the convergence of the turnout giving rise to fatigue, resulting in a partial fracture of the local area.
Publication Details
Li, H., Carkagis, M., Hellier, A. K., Zhu, H., McLeod, J. & Pannila, S. (2017). Railway turnout failure mode analysis. 9th Australasian Congress on Applied Mechanics (ACAM9) (pp. 324-331). Sydney: Engineers Australia.