Damage Identification Based On The Broad Frequency Responses Of Piezoelectric Sensors

The piezoelectric materials (such as Pb-based Lanthanumdoped Zirconate Titanates, PZT), due to their low costs and excellent dynamic properties, have broad application prospects in structural health monitoring of civil engineering. However, even though the PZT sensors have broad frequency responses, only partial frequency range of PZT signal tends to be used. There are still further studies to be done on the dynamic properties of sensors and multi-functional applications based on the broad frequency range of piezoelectric sensors. This paper focuses on the damage identification based on the broad-frequency responses with the range from 0 to 300kHz of piezoelectric sensors. The detailed works are as followed.(1) The "PZT-bonding layer-host structures" model, which is considered as the dynamic shear strain transform model of layered medium, is proposed for the coupled system of pasted PZT sensor and host structure. The effects of dynamic strain transform properties caused by driving frequency are analyzed. In addition, the dynamic properties of sensors caused by PZT thickness, bonding layer material and thickness are also analyzed. The validity of proposed method is proved by both ANSYS and experiments.(2) The dynamic properties of embedded PZT sensor under broad frequency range excitation are analyzed. The "PZT-water proof layer-protecting layer" model, considered as the dynamic mechanical model of layered medium for embedded PZT sensor, is proposed. The effects of dynamic stress transform properties of PZT sensors caused by driving frequency are analyzed by the proposed model. In addition, the effects of sensor dynamic property, caused by manufacture craftsmanship such as materials and thickness of both protecting and water-proof layer, are then analyzed. The effectiveness of above analysis is verified by both ANSYS and experiments.(3) The formation mechanism of beat signal from low frequency response of PZT sensor in structural impact test is analyzed in the view of mathematics. The effecting factors of beat signal, such as damper effect, impact direction and position of sensor, are then analyzed by the rotate vector method. In addition, an impacting direction identification method, based on the beat signal of PZT sensor, is proposed. The correctness of proposed method is finally verified by the impacting test of steel column.(4) A damage identification method used low frequency range of PZT signal, which is based on cross-correlation function amplitude and support vector machine, is proposed. The proposed method only needs the responses of structures and is adapt for arbitrary excitations. The IASC-ASCE benchmark model is used to testify the availability of method. Moreover, the proposed method is also proved to have excellent identification effects for the damage detection of truss model.(5) Based on the broad-frequency responses of PZT sensor, a multi-functional monitoring method combining vibration test and acoustic emission monitoring is proposed. The dynamic bending test of concrete beam is taken as an example to illustrate the multi-functional monitoring on concrete members. Then the PZT sensors are applied for monitoring RC frame-shear wall structures subjected to seismic loadings. The dynamic properties of structures and local damage status are analyzed for the multi-function of PZT sensors.