Browsing by Author "Khodabakhshi, B"

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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
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    Investigating the effect of pre-heating on the magnitude of residual stresses in aluminothermic rail welds using neutron diffraction
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2013-12-02) Khodabakhshi, B; Paradowska, AM; Mutton, PJ; Ibrahim, R
    Aluminothermic rail welding is an in-track process which continuously welds rail tracks on site. This weld has a high rate of failure due to its cast structure and variable quality. The existence of residual stresses which are developed during the casting process is one of the main factors affecting the formation and propagation of the cracks in the foot and head of the rail. Magnitude of these stresses depends on the welding parameters such as preheating. Hence, it is desirable to determine the correlation between the residual stresses and welding parameters in order to decrease the residual stresses and increase the life span of these welds. In this paper, the effect of pre-heating on the magnitude of residual stresses in the foot and head of the rail weld is investigated using strain scanner Kowari at ANSTO. Previously, residual stresses in these welds have been measured using neutron diffraction. However, this is the first time that measurements are conducted for a full sample non-destructively. The results indicated that the magnitude of residual stresses decreases by optimizing the preheat procedure, and this is quite promising and can assist the railway industry to improve the integrity of the rail welds in future.
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    Measurement of residual stresses in aluminothermic rail welds using neutron diffraction technique
    (Scientific.Net, 2014-02-01) Khodabakhshi, B; Paradowska, AM; Ibrahim, R; Mutton, PJ
    It is understood that residual stresses in aluminothermic rail welds play an important role in the fatigue behaviour of the welds. Measuring the residual stresses in the critical areas and finding the correlation between these stresses and welding parameters can be useful in order to alter the welding procedure and improve the fatigue performance of these welds. In this paper, residual stresses in the foot of the rail weld were measured using neutron diffraction and the preliminary results are presented. © 2021 by Trans Tech Publications Ltd.
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    Measurement of residual stresses in aluminothermic rail welds using neutron diffraction technique
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-09) Khodabakhshi, B; Mutton, PJ; Paradowska, AM; Ibrahim, R
    Aluminothermic welding is widely used as an in-track process to continuously weld rail tracks on site. This process provides increased flexibility compared to the use of mobile Flashbutt welding equipment; however the cast structure and variable quality results in increased failure rates. One of these failure modes is straight break which initiates at the edge of the weld collar in the lower head and upper foot sections. In order to examine the fatigue behavior of the weld by using multi-axle fatigue analysis, residual stresses in critical areas need to be investigated. In this paper, we are showing preliminary neutron diffraction residual stress measurements in the critical region of the rail foot area at two sides of the weld collar, which have been determined using strain scanner Kowari at ANSTO. The result shows high longitudinal stresses in the location which is prone to the failure approximately 50 mm away from the weld's toe. The pros and cons of the measurement technique in relation to the weld rails components will be discussed and future research plans will be presented.