Contactless Non-destructive Testing of Railway Axles with the GCLAD Optical Technique

Abstract Railway axles, though designed to last over 20 years, are fatigue-stressed components that may suffer premature failures with severe consequences. Ultrasonic techniques are among the most effective inspection methods, but their limitations–such as the need for physical coupling with the axle and long inspection times–have encouraged the exploration of innovative, contactless solutions. This paper presents the setup and analysis of ultrasonic data collected using Gas-Coupled Laser Acoustic Detection (GCLAD), while employing a pulsed laser as the emitting source. GCLAD is a contactless technology that enables point detection of waves in transmission and reflection at once, offering multiple opportunities to identify defects and discontinuities. The present preliminary study demonstrates the feasibility of inspecting railway axles without disassembling wheelset components, through a fully optical system that acquires and detects ultrasonic waves without contact. This approach maximizes automation and reduces inspection-related times. The devised experimental layout successfully identified defects in the wheel seat area (down to 2.7 mm), brake seat area (7.5 mm), and axle body (0.95 mm), even with mounted wheels. An industrial application highlights the potential suitability of GCLAD-based instrumentation for integration into actual inspection apparatus, supporting efficient monitoring of railway axles while paving the way for improved automation and reduced inspection times.