Leaky and non-leaky behaviours of guided waves in CF/EP sandwich structures

•The behaviour of guided waves in honeycomb and foam composite sandwich structures was studied.•The thickness of the honeycomb core greatly affects the magnitude of the wave mode.•The increase in excitation frequency results in mode conversion from guided waves to the Rayleigh wave.•The A0 appears to have both leaky and non-leaky behaviours.•The S0 mode appears always to have a leaky behaviour.

The aim of this study is to investigate the leaky and non-leaky behaviours of guided waves, between the composite skin and the core in CF/EP sandwich structures, focusing on the fundamental symmetric like and anti-symmetric like guided wave modes and Rayleigh waves. In investigating the core effect on the guided wave propagation different types of cores are used, namely Nomex honeycomb (HRH 10 1/8-3) 10 and 20 mm in thickness and foam (Divinycell®  PVC). The behaviour of the guided wave modes is characterised and the conversion mechanism to the Rayleigh wave is investigated. Further, leaky and non-leaky behaviours of guided waves upon interacting with debonded areas are explored, where the ability of guided waves to identify debonding of different sizes was assessed. Finite element analysis simulations are presented to support the experimental analysis, where propagation of ultrasonic waves and their interaction with debonded areas are quantitatively examined.