Investigation of residual stress in aluminothermic and flash-butt rail welds using neutron diffraction

2017-02-21T02:58:37Z (GMT) by Khodabakhshi, Bahar
This thesis seeks to improve residual stress measurement techniques in large components with complex geometries using neutron diffraction. In this work, residual stresses in rail weld samples were measured at locations in welds where traditional methods of measurement are not able to access. This is the first time that full scale rail welds were used for neutron diffraction measurements. The procedure used in these measurements can be used to measure residual stresses more accurately and with higher resolutions in structures with complex and large geometries. Residual stresses in four rail samples were measured at locations where welds are more prone to crack and fracture. Two of the rail welds were made using aluminothermic welding technique, and they had different preheating conditions. Other two samples were made through flash-butt welding technique, and different welding machines were employed to make them. Using the measured residual stresses, the correlation between railway welding techniques, some of the welds' metallurgical characteristics and the measured residual stresses were determined. This work can be used as a stepping stone toward weld optimization procedure in railway industry by minimizing the magnitude of residual stresses, and it adds to understanding of measuring residual stresses in full scale samples, lattice parameter measurements in reference samples and determining the correlation between welding parameters and residual stresses in rail welds. The result obtained through these measurements can be used as a sound base for fatigue analysis and life span prediction of rail welds.