Multi-mode vibration detection for delamination of carbon fibre composite plate

The vibration-based structural health monitoring (SHM) has been widely studied in the damage identification field. Due to the damage, the physical parameters of the structure would be changed, which may affect the dynamic response of the structures, such as natural frequencies, damping ratio, phase, mode shape, etc. And the parameter changes could be used to predict and estimate the damage information. At present, most SHM studies focused on the frequency changing of composite plate, but the damping as a more sensitive parameter has not been adequately utilized. In this paper, the multi-mode vibration detection method is proposed, which combined with the natural frequencies and damping of the composite plate to identify the delamination information. Through simulating the effect of damages on composite plate with finite element software COMSOL, the one-to-one mapping relationship between multiple modes natural frequencies and the size and in-plane location were obtained, and the mode 3rd and mode 5th were selected to predict the delamination. In the experiment, carbon fibre composite plates with artificial delamination were fabricated. The vibration mode signals were detected by piezoelectric materials and analysed by FFT and Hilbert transform to calculate the natural frequencies and damping ratios of composite plates. By the inverse problem method, the predicted values of X-location were consistent with the actual location of delamination in experiment, which the error was less than 3%.