IN‐SITU MONITORING OF FATIGUE CRACK GROWTH AT FASTENER HOLES USING RAYLEIGH‐LIKE WAVES

The development of fatigue cracks at fastener holes is a common problem in aircraft maintenance. This contribution investigates the use of Rayleigh‐like waves for the in‐situ monitoring of fatigue crack growth in tensile, aluminum specimens. Experimentally the Rayleigh‐like wave is excited using standard angle beam transducers and measured using either standard pulse‐echo equipment or laser interferometry. The combined scattered field of the Rayleigh‐like wave at the fastener hole and crack is measured and compared to finite difference (FD) simulations. The measured changes in the pulse‐echo ultrasonic signal due to fatigue crack growth are evaluated using an energy ratio parameter and correlated to the optically measured crack length.