Disbond detection in composite adhesively bonded T-joints using vibration signatures

Work carried out in this project is based on extending the acoustic tap technique for application to an in-situ health monitoring method to detect disbonds in glass fibre reinforced plastic composite (GFRP) T-joint structures. Experiments were performed on T-joint specimens and plate specimens to determine if it is possible to quantify the effect of damage on the acoustic response resulting from a force excitation. The samples tested had varying degrees of damage, primarily in the form of Teflon inserts to simulate a disbond. Two of the T-joint specimens tested had failed during a mechanical test which produced large delaminations throughout the bonded interfaces in the structure. For each set of specimens tested one of the samples was undamaged. The force excitation was applied using two different methods: a force hammer and a piezoelectric actuator. The presence of disbonds could be clearly identified by distinguishable features in the frequency spectra of the acoustic response, particularly for the piezoelectric actuator input.