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 developing safer and more efficient maintenance strategies. This extended abstract details an experimental study on fatigue crack growth behaviour in flash-butt welds in a hypereutectoid rail steel with a hardness level of over 400 HV. 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 the marker band method as well as to analyse the morphology 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 current work will provide a reliable database for predicting rolling contact fatigue crack growth at different regions in flash-butt rail welds.
EXTENDED ABSTRACT