Scanning pulse phase thermography for surface defect detection in manganese steel turnout frogs

Austenitic manganese steel is a commonly used material for railway turnout frogs due to its beneficial mechanical properties. In service, surface defects caused by rolling contact fatigue (RCF) can occur and need to be detected and assessed during maintenance intervals. In this work inductive scanning pulse phase thermography is used to localize these surface defects. During scanning the surface of the frog is heated (∆T<5K) with an air-cooled inductor. The surface temperature is recorded with an infrared camera. A registration target is also recorded in each frame of the image sequence. This method recognizes the movement in the sequence itself without external sensors. Furthermore, by using a registration target it is also possible to scan manually, as motion speed is calculated frame by frame. For the evaluation, the recorded sequence is transformed such that the turnout frog and the registration target seem to be stationary. In this new sequence the temporal changes in temperature of each pixel of the surface are evaluated by Fourier transform to a phase image. The evaluation via phase image is known to be robust to negative effects such as inhomogeneous heating and emissivity. This work aims at developing a mobile prototype, which allows service personnel to use scanning pulse phase thermography to localize and characterize surface defects on manganese steel turnout frogs during maintenance.