Browsing by Author "Salehi, I"

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    Aluminothermic welding of rails: Improved qualification and performance under heavy haul conditions
    (Railway Technical Society of Australasia, 2014-01-01) Salehi, I; Khodabakhshi, B; Mutton, PJ; Paradowska, AM
    Aluminothermic welding continues to be used widely throughout the rail industry, due to its low capital cost and flexibility of use. A range of weld types are available from the two manufacturers who support the Australian market; these vary in terms of collar design, preheating conditions, etc. Single-use crucibles, which are now commonly used, have overcome some of the inherent disadvantages of multi-use crucibles. However the reliability of aluminothermic welds continues to be lower than that of flashbutt welds, particularly under heavy haul conditions where aluminothermic welds are responsible for the majority of rail defects and broken rails. Failure modes in aluminothermic welds can vary depending on the characteristics of the individual weld type and the service conditions, although the majority of failures are associated with fatigue cracking at the top or underside of the rail foot. Other failure modes include fatigue cracking in either web or underhead regions; these modes are strongly dependent on the weld collar design and residual stress levels. Qualification requirements for aluminothermic welds in the current Australian standard include mandatory fatigue testing of the rail foot, and an optional web fatigue test which is generally applied when approving welding procedures for some heavy haul conditions. At present there is no established test procedure for fatigue of the underhead region. Several concurrent activities being undertaken with the support of both consumable manufacturers and some heavy haul rail systems, in conjunction with the Australian Nuclear Science and Technology Organisation (ANSTO), aimed at improving the reliability of aluminothermic welds. These include neutron diffraction measurement of residual stress levels in the critical regions of the weld collar, development of a fatigue test methodology for the underhead region, and an enhanced welder training and audit program which provides the opportunity to address any issues with consumables or equipment in a timely manner. © 2014 Railway Technical Society of Australasia