Baseline-free Guided Wave Imaging Method for Detection of Nonlinear Defects in Plates

The reconstruction Algorithm for Probabilistic Inspection of Damage (RAPID) has already shown to be an effective baseline-dependent SHM technique for damage detection and localization. It has proven its ability, in combination with ultrasonic sparse array, to detect different types of damage in plate-like structures, e.g. corrosion patches or impact damage. RAPID has been tested in a range of different materials spanning from aluminum to carbon-fiber-reinforced polymers (CFRP). However, the ultimate goal of the ultrasonic sparse array SHM system is to able to detect damage without the knowledge of baseline signals. In this contribution, we would like to present a novel approach to the baseline-free guided wave imaging that builds on the basics of the conventional RAPID algorithm. The Scaling Subtraction Method will be utilized in order to replace the intact baseline signals by the signals obtained at the different excitation amplitude levels. It will be shown that by adopting this approach, the nonlinear defects, such as delaminations, can be detected and localized in the CFRP plates. Experimental results will be presented as well as supporting numerical simulations. Furthermore, we will discuss the potential of the Local Defect Resonance (LDR) phenomena to improve the results of the proposed baseline-free probabilistic guided wave imaging.