Debonding detection in CFRP-reinforced steel structures using anti-symmetrical guided waves

Carbon fibre reinforced polymer (CFRP) has proved to be effective in strengthening ageing steel structures, due to its outstanding properties. However, debonding problems which can occur at the interface severely impair the performance of retrofitted structures. In this paper, a guided wave based structural health monitoring (SHM) method is employed to detect debonding in CFRP-reinforced steel structures. The proposed samples are CFRP-reinforced steel plates with different sizes of debonding. Due to its sensitivity to interfacial damage, the anti-symmetrical Lamb wave mode is chosen as the incident wave and surface-mounted piezoelectric (PZT) wafers are employed to excite and collect the signals. Theoretical derivation is introduced to find the relationship between the time-of-flight (ToF) of the first arrival wave package in the received signals and the extent of debonding damage. A linear relationship is obtained, in that the ToF decreases linearly with the increase in the size of debonding. When corresponding numerical simulation and experimental study are performed to verify the relationship, similar trends are observed.