Study On Structure Initial Crack Monitoring Based On Piezoelectric Impedance Technique

The engineering structure is affected by the environment in the process of service,which inevitably produces local damage,and the local damage will cause component failure and even catastrophic accidents to a certain extent Among these local injuries,cracks are the most common.The initial state of cracks is in the form of microcracks,so it is particularly important to identify the occurrence and propagation of these cracks for the normal work of the structure.Aiming at the initial crack of engineering structure,the method based on the peak frequency offset of piezoelectric impedance is applied to the monitoring of initial crack,The key problems of the method are studied by using theoretical analysis and finite element simulation,and the corresponding experiments are designed and verified.The main research work in this paper is as follows:(1)According to the electric admittance formula of the electromechanical coupling structure,the related expression of the admittance peak frequency and the rigidity of the main body structure is obtained.The generation and propagation of cracks in the structure will reduce the stiffness of structure,and the decrease of the stiffness of the structure will cause the resonance frequency of the coupling system to shift,so that the degree of crack can be judged by the offset of resonance frequency.This provides theoretical support for monitoring the occurrence and development of structural cracks.(2)The finite element simulation model of cracked beam is established.The results of modal analysis and piezoelectric harmonic response show that the peak frequency of piezoelectric admittance signal is a certain order resonant frequency of host structure,which indicates that the piezoelectric impedance method can effectively detect the dynamic characteristics of host structure.Finite element software is used to simulate the variation trend of piezoelectric admittance signal under different crack levels,and the relationship between the peak frequency of admittance and the crack size is obtained.(3)A beam test device is constructed to study the influence of different crack sizes and frequency bands on the peak frequency of admittance of piezoelectric materials,which are installed on the surface of aluminum beam.The simulation and experimental results show that the peak admittance frequency of piezoelectric materials decreases with the increase of crack damage.Under the same damage degree,high resonance frequency is more sensitive.This sensor system can well identify small size initial cracks.By applying this method to the early structural pore monitoring experiment,we can well monitor the expanding change of the pore diameter.