Abstract: Delamination damage is one of the common damage in composite materials, and it will gradually expand with the extension of working time, which will seriously weaken the strength and stability of composite materials. At the same time, the delamination damage at different interfaces will also cause various mechanical changes to different degrees. Therefore, it is of great significance for the overall safety of the structure to effectively identify, locate and expand monitoring it. In this paper, a Lamb wave-based ToF delamination damage monitoring method is proposed. By comparing and analyzing the Lamb wave ToF differences between the upper and lower surfaces of composite laminates, the damage interface of composite laminates with an initial delamination damage is located, and the delamination damage expansion at different interfaces is continuously monitored online. Firstly, the principle of Lamb wave monitoring delamination damage is studied. Secondly, the relationship between the depth and length of the delamination damage interface and the propagation speed of Lamb waves in the structure was established, and the theoretical basis for the location and extension monitoring of the delamination damage interface was obtained. Finally, the effectiveness of the proposed method was verified by finite element simulation. The simulation results show that the shallower the delamination damage interface is from the laminate surface, the more significant the Lamb wave signal delay, and the greater the difference in signal time between the upper and lower surfaces, moreover, the signal delay is linearly related to the increase of delamination damage length.

Key words: structural health monitoring, composite structure, Lamb wave, depth of damage interface, delamination extension monitoring