An Analysis of UT Echoes Coming from Fatigue Cracks and Artificial Defects on Railway Axles

Non Destructive Testing applied to railway axles is performed both in production and in maintenance. During production, NDT is carried out at different stages adopting different techniques, while during maintenance (in-service inspection) only ultrasonic testing is usually carried out. The present paper is focused on some aspects of calibration related to the in-service inspection of railway axles by means of ultrasonic NDT. In particular, applied standards request to calibrate sensitivity on suitable reference blocks provided with notches. In order to investigate the performance of these notches in respect to real cracks, the echoes coming from fatigue cracks generated onto hollow axles made in A4T steel by means of a dedicated test bench have been compared with those detected from suitable reference blocks. The results suggest some clues for designing effective sample blocks for railway axles.