Surface defect detection in stiffened plate structures using Rayleigh-like waves

This contribution deals with the use of coupled Rayleigh-like waves for the remote detection of defects in stiffened plates similar to aerospace structures, where access is restricted by regularly spaced features such as stiffeners or stringers. Selecting appropriate excitation frequency and position, it is shown experimentally that a significant part of the energy can be transmitted past multiple obstacles, which act as a band-pass filter. Using a standard Rayleigh angle beam wedge transducer in a pulse-echo configuration, a surface defect (notch) located behind three stiffeners more than half a meter from the measurement position is detected experimentally. The detection sensitivity for different defect depths and locations relative to the structural features is discussed based on finite-difference simulations.