Improving the reliability of aluminothermic rail welds under high axle load conditions

Abstract

Aluminothermic rail welding is widely used as an in track welding process due to its low cost, fast installation and equipment portability. Despite operational preferences, aluminothermic welding suffers from variations of the produced weld quality and defects which are the result of its cast-like process. As a consequence the probability of aluminothermic service failures may be higher than the parent rail, particularly under high axle load conditions. This paper addresses the risk of weld failure though the development of an analytical approach to assessing the fatigue behaviour of aluminothermic welds, and the development and implementation of an enhanced welder training and competency program which has contributed to a significant decrease in defective welds. The bending behavior of aluminothermic weld is investigated around two most important failure modes for heavy haul operation: horizontal split web (HSW) and straight break. Due to the cyclic nature of the applied loads, these failure modes are overseen in the context of fatigue crack analysis which involves fatigue crack initiation and propagation assessments. However, it is believed that the material distress as a result of wheel-rail contact stress, bending, weld residual and seasonal thermal stresses as well as weld geometry would highly affect the failure initiation sites and the life to crack initiation of the weld. In order to investigate the weld material distress, a thermo-structural finite element model of the rail weld has been developed incorporating the track stiffness behavior to enable us superpose the seasonal thermal effects with local bending and contact stresses. The effect of some heavy haul parameters such as contact patch lateral movement due to curving or hunting with various traction coefficients are also investigated. The simulation results show a good consistency between the bending behavior of the weld and fatigue crack initiation probability based on observations. The current study forms the basis for a comprehensive fatigue crack initiation analysis as the next stage of the project