Novel Low Acoustic Impedance (LAI) Transducer For Damage Detection

The manufacturing and validation of a novel Low Acoustic Impedance(LAI) is presented in this research. The proposed system relies on an active piezoceramic PZT(Lead-ZirconateTitanate) transducer, as well as an I/O electronic circuit and software are used to excite the transducer and monitor its response. The behavior of the PZT transducer can be related to the mechanical impedance changes of the target structure. Since the presence of defects affects the local mechanical response of the target structure, the defects can be detected by monitoring changes in the structure's impedance with the PZT transducer.In the first part of the thesis, various common Non-Destructive Evaluation(NDE) techniques such as ultrasound, x-ray and thermography are reviewed and the fundamental physical electromechanical behavior of piezoelectric transducers is also introduced. The LAI technique fundamentals, features and advantages are discussed. The detailed description of the design and fabrication of the proposed system including a transducer, the I/O electronics, and controlling software is provided.Finally, the experimental results and numerical models are introduced to verify the effectiveness of the proposed system and transducers. The verification is done by different fiberglass – epoxy composites, wooden and polymer specimens. The LAI technique proved the ability of defect's detection successfully. For example, the technique has been tested on fiberglass-epoxy composite plates which have been subjected to impact by drop weight impactor and the normalized impedance values have been presented in line and surface plots. In the case of composite plates, the technique could detect the presence and approximate dimension of the defects as well. The threshold of impact's energy was another key result for composite plates which it has been calculated around 3J for the specific composite plates and test specifications in this thesis. The results of side experiments by polyacrylamide gel and edible gelatin are introduced as well. The results of polyacrylamide gel seem noisy compared to composite and wooden specimens. The origin of this noise could be the damping effect of the gel, surface effects and particle's size as well. In addition that 2D numerical models using available commercial software were created and processed. Despite the simplicity of the system in comparison to other complex NDE techniques, the experiments and numerical models verify the ability of LAI's technique in defect's detection effectively. The LAI can be considered a cost–effective and user-friendly NDE technique because of its simplicity and proven effectiveness in detecting damage.