Development of High-speed inspection Technique Based on Motion Induced Eddy Current Testing for Surface railway Defects

Thailand’s rail system has transitioned from a minor role in transportation to becoming a primary mode of travel and freight transport, driven by government investments in double-track rail development. High-speed rail projects, e.g., the Thailand-China railway, are in progress to enhance the capacity and efficiency of train transportation. Due to the growth of railway construction and services, increasing rail usage has led to higher risks of surface defects such as cracking, rolling contact fatigue, head checks, and spalling. Currently, non-destructive testing (NDT) methods including Visual Testing, Magnetic Particle Testing, Ultrasonic Testing, and Eddy Current Testing, face challenges in accuracy, speed, and sensitivity during high-speed inspections.

To overcome these limitations, this study proposes a modified technique of induced-motion eddy current testing based on the self-induced magnetic field principle to generate eddy currents flowing in the conductive specimen under testing. Detection probes were designed and developed with a distinctive configuration of permanent magnets and tunnelling magnetoresistance (TMR) sensors, established through numerical simulation and experiments. A high-speed motion machine was also designed and developed to simulate railway testing, with controllable testing velocities between 1 and 30 km/h. Artificial linear and round surface defects were introduced for experimentation. Sensitivity, resolution, and inspection velocity were studied. Results show that the developed motion-induced eddy current technique can distinguish linear defects—transversal and longitudinal cracks—as small as 0.5 mm wide and 1 mm deep, and round defects of 2 mm diameter and 1 mm depth, at inspection velocities up to 30 km/h. Furthermore, there were only small changes in inspection signals across different testing speeds. Consequently, the development of a high-speed inspection technique based on motion-induced eddy current testing is promising for enabling precise, high-speed rail inspections and improving the safety of rail transportation.