Baseline-free damage imaging for metal and composite plate-type structures based on similar paths

Lamb wave–based structural health monitoring technology has attracted great interest and wide attention. Most of the Lamb wave–based structural health monitoring algorithms utilize scattering signals subtracted between baseline and current signals, which are recorded before and after damage and are easily influenced by environmental changes. In this article, a baseline-free method based on similar path is proposed to identify the damage in metal and composite structures. Due to Lamb wave scattering on damage, the first wave packet of signal for the transmitter–receiver path passing through or near the damage will be weakened. Based on sensor spacing (and direction for composites), all transmitter–receiver paths of transducer array can be classified as some groups, each having similar paths. The first wave packet energies of the paths in the same group are compared with each other to calculate damage indices, which are used to image the damage. Simulations were carried out to identify single- and multi-damages in the metal and composite plates. In addition, an experiment was also conducted to verify the algorithm. Both simulation and experimental results demonstrate the feasibility and effectiveness of similar path-based damage identification method.