Multi-axial fatigue analysis of aluminothermic rail welds under high axle load conditions

Fatigue crack initiation analysis is performed at the edge of the weld collar of an aluminothermic weld, in order to examine one of the failure modes that occur in this weld type under high axle load conditions. Since the stress state is multi-axial and the stress history involves rotating principal stresses, a shear based multi-axial fatigue criterion based on the concept of critical plane is exploited. It is believed that the material distress as a result of wheel–rail contact, bending, residual and seasonally-dependent thermal stresses, as well as the geometrical features associated with the weld collar, would directly influence the location of fatigue crack initiation and the severity of damage. The fatigue assessment is performed using thermo-structural finite element analysis followed by the Dang Van multi-axial fatigue criterion implemented as a customized computer code. The method is applied to investigate the effect of operational parameters including the conditions of vehicle hunting or curving, residual stress, seasonally-dependent variations in rail temperature, and deficiencies in track support conditions in the vicinity of aluminothermic welds. The finite element simulation is validated through strain gauge measurements, and the results of fatigue analysis are compared with the locations of fatigue cracking and failure modes that occur in-service.