Ultrasonic Surface Wave Propagation and Interaction with Surface Defects on Rail Track Head

Abstract

Electromagnetic acoustic transducers (EMATs) are non‐contact ultrasonic transducers capable of generating wide band ultrasonic surface waves on metallic samples. We describe some lab based ultrasonic measurements using EMATs to generate a wide band, low frequency (approximately 50–500 kHz) ultrasonic surface wave, with Rayleigh wave‐like properties on a rail head. A Michelson interferometer has been used to accurately measure the absolute out‐of‐plane displacement of the ultrasonic waves generated on the rail head which propagate along the rail head to interact with a simulated surface breaking defect. Some of the energy is reflected from the defect and some propagates under the defect. We describe different approaches that can be used to determine the presence and depth of the crack and present the data as a range of ultrasonic B‐scans. The non‐contact nature of EMATs and the pitch‐catch test geometry that we propose to use for testing make them especially suitable for online detection and gauging of crack depth at high speed.