This thesis systematically evaluates the influence of composite thickness on properties of ultrasonic guided waves (UGW) under varying temperatures for damage detection using surface-mounted and embedded lead zirconate titanate (PZT) transducers for Structural Health Monitoring (SHM) purposes.
First, a novel edge cut-out method for embedding diagnostic films with PZT transducers based on the circuit-printed technique will be proposed. The use of thin diagnostic films with printed circuits instead of traditional cables was shown to significantly reduce the weight of composite structures. In addition, the novel edge cut-out method allowed edge trimming possible which can be used in industrial mass manufacturing for the next higher assembly.
Then the structural integrity of the composites with the embedded diagnostic film and PZT transducers will be assessed. Initially, the effect of fatigue tests on the electro-mechanical impedance (EMI) properties of PZT transducers under different loading cycles (up to 1 million) was studied. In addition, the effect of fatigue tests on active sensing behaviours based on UGW under different loading cycles was investigated. Finally, the tensile and compressive tests were conducted to assess the effect of the novel embedding technique on the elastic modulus of the composite materials.
After that, the peak amplitude and the group velocity of the S0 and the A0 modes and temperature influence through different thicknesses of composites actuated by surface-mounted and embedded PZT transducers will be investigated. The interactions of UGW with the surface-mounted artificial damage and the impact damage were studied by laser Doppler vibrometer (LDV) using surface-mounted and embedded PZT transducers. Finally, damage detection and localization for the surface-mounted artificial damage and the impact damage were investigated by surface-mounted and embedded PZT transducers. The influence of the embedded position of PZT transducers on UGW was also numerically and experimentally studied. The reversibility of the peak amplitude of the first wave packet of UGW actuated/received by PZT transducers in different positions was compared.
In the end, the possibility of monitoring the debonding and the simulated damage of the composite bonded by a repair structure using a smart repair patch will be investigated. First, the EMI method was used to verify the bonding properties of PZT transducers. Second, the damage index (DI) correlation coefficient and the delay-and-sum (DAS) algorithm were used to detect and locate the artificial delamination and the surface-mounted artificial damage, respectively.