Research on Rail Stress Detection Based on Electromagnetic Ultrasonic Method

In-service seamless rails are subjected to complex combinations of residual and operational stresses, and accurate assessment of their internal stress distribution is essential for maintaining track integrity and operational safety. This study introduces a noncontact nondestructive rail stress measurement approach that integrates electromagnetic acoustic transducers (EMATs) with surface-wave acoustoelastic theory. A novel EMAT with conformal meander-line coils integrated with an array of permanent magnets was designed to achieve consistent coupling with the rail head surface and efficient surface wave excitation. Key transducer parameters were optimized through simulation-based orthogonal experiments. A stress loading platform applied varying axial stresses to rail specimens; resulting changes in ultrasonic propagation time were observed to extract the acoustoelastic constant and establish a mapping between stress and time delay. Finally, an automated scanning system was utilised to measure full-length surface stress distributions on retired rail segment, revealing stress patterns closely associated with the rail’s service history and geometry. The proposed system achieved a measurement accuracy within 22 MPa and demonstrated high repeatability, indicating its potential as a reliable and efficient NDT method for stress evaluation of seamless rails.