Mixed mode fatigue crack growth behaviour under microstructural variation in flash-butt welds

The strength loss due to welding process poses a high risk of catastrophic rolling contact fatigue failure in the heat affected zones of flash-butt rail welds. Accurate characterisation of fatigue crack growth behaviour in such regions can provide a database for customising safer and more efficient maintenance strategies. This extended abstract detailed an experimental study on fatigue crack growth behaviour in flash-butt welds in a hypereutectoid a rail steel with hardness level of over 400HV. Groups of mixed mode fatigue crack growth tests were carried out at parent rail region, partially spheroidised region, fully spheroidised region, re-austenitised region and bond line region. Fractographic analysis was performed to aid the application of marker band method as well as to analyse the topology of fracture surfaces. Once all experiments are finished, an equivalent stress intensity factor formula will be fitted to quantify the mixed mode crack driving force in different regions, and modifications of crack growth direction prediction criteria will be proposed for crack growth under the influence of microstructural variation. The proposed model will be checked against all the experiment data. The current work will provide a reliable database for predicting rolling contact fatigue crack growth at different regions in flash-butt rail welds.