Evaluation of ultrasonic non-destructive inspection methods for structural integrity assessment of freight train axles

Structural integrity assessment aims to ensure compliance with specified safety, strength, and performance standards. It operates on the principle of damage tolerance, ensuring that failure is avoided as long as the structure remains within its load-bearing capacity, despite the presence of defects or cracks, according to fracture mechanics criteria. By combining the probability of detection from the NDI procedure, the damage tolerance concept ensures the safety of the axle during operation. This study examines the sensitivity of the NDI method in detecting damage and compares its results with the structural integrity assessment criteria outlined in BS 7910. To obtain accurate analysis results, this study utilized numerical simulations with the finite element method using ANSYS software. The results indicated that the critical defect size is 80 mm according to the criteria specified in BS7910. In addition, the sensitivity analysis of NDI showed that NDI can detect the smallest defect size of 4 mm, albeit with a very low indication pulse, and can detect defects with a sufficiently good detection pulse at a defect size of 10 mm.