Dynamic behaviour of piezoelectric sensors and their application in crack identification for SHM

Abstract: The health monitoring of critical structures plays a crucial role in locating damage positions timely and preventing catastrophic failures. Much attention has been devoted to exploiting piezoelectric sensors/actuators to develop techniques of recording elastic wave signals to realize structural health monitoring (SHM). This thesis is to conduct a systematic investigation of the dynamic behaviour of piezoelectric sensors and their application in quantitative crack identification in SHM systems. A typical SHM system contains piezoelectric sensors bonded to a host structure to be monitored. This structure is subjected to a dynamic excitation which will induce elastic wave propagation in it. When the wave encounters cracks, it will be scattered and the scattered wave will be recorded by the piezoelectric sensors. The recorded signals contain the information of the cracks thus can be used to identify the parameters of the cracks. In this study, theoretical modelling and simulation are conducted to investigate the load transfer between the sensor and the host structure, the dispersion relation of wave propagation, and the multiple scattering of elastic waves. In addition, a crack identification technique is investigated using the voltage signals based on optimization method. Four aspects of the work were accordingly studied and examined. Firstly, a new model is developed for surface-bonded piezoelectric thin-sheets with bending effect. The coupled electromechanical behaviour and the effect of bending upon load transfer and local stress field are studied. Secondly, a new analytical treatment is provided for wave propagation in layered piezoelectric structures, including dispersion characteristics and harmonic wave propagation. The two lowest wave modes of the guided wave in such structures are analyzed. Thirdly, a new semi-analytical solution is determined for the complicated dynamic interaction between piezoelectric sensors and cracks using pseudo incident wave method and superposition. This method has the advantages of the reliability of analytical solutions and the flexibility of typical numerical methods, and finds explicit relations between the voltage output of the piezoelectric sensor and the crack parameters. Inversely, by integrating this relation and known voltage data into an optimization process, a novel crack identification technique is established. This technique quantitatively identifies the position, the length and the orientation of typically embedded cracks effectively. The methods proposed in this thesis can be used to understand the dynamic behaviour of piezoelectric based SHM systems, multiple scattering of elastic waves and provide insights into developing new methods for quantitative crack identification.