Ultrasound real-time imaging of crack propagation during ultrasonic fatigue tests

This Letter describes a real-time surface inspection method based on ultrasonic synthetic imaging using Rayleigh waves. The proposed method can be employed to monitor crack propagation during ultrasonic fatigue tests. The setup, which is highly sensitive to cracks, enables the imaging of a large surface (tens of mm2), with spatial resolutions of several tens of micrometers and an imaging frequency of up to 50 frames per second. The micrometric resolution allows cracks to be investigated at the grain level, while the sample imaging enables high-velocity crack propagation to be accurately resolved. These two domains have rarely been investigated to date because of experimental limitations. This work paves the way for a new type of laboratory-scale fatigue monitoring based on crack propagation, leading to better comprehension of the associated physical phenomena.