Thermography methods and modelling approaches for rail foot flaw detection

Rail foot flaws have the potential to cause broken rails which can lead to catastrophic derailments. This is not only an extremely costly issue for a rail operator in terms of damage to rolling stock, but has significant flow-on effects for network down-time and a safe working environment. In Australia, heavy haul operators run up to 42.5t axle loads with trains in excess of 200 wagons and these long trains produce very large cyclic rail stresses. The early detection of foot flaws before any rail breaks occur is of high importance to their safe and cost effective operation. This paper will present a brief review into the current methods for rail flaw detection with an emphasis on thermography, discussing apparent strengths and weaknesses. Thermography is a common Non Destructive Testing method used for the detection of temperature differentials on the surface of a structure that may be indicative of a flaw. Approaches for modelling of the wheel/rail interface for calculation of the rail stresses and determination of expected infrared radiation will be presented, along with an investigation into potential sensors that may be useful for a field device suitable for Australian heavy haul railway operating conditions.