Application Of Piezoelectric Impedance Decoupling Technique In Monitoring Of Bolt Connection State

The loosening or failure of the bolt connection may lead to equipment failure,what's worse is caused property loss and casualties.Therefore,it is great significance to real-time monitoring of bolt connection structure.This paper,the monitoring method of bolt looseness is studied that based on the piezoelectric impedance technique.The main contents are as follows:(1)Based on the piezoelectric effect equation,the piezoelectric impedance technique is analyzed,and the admittance equation of PZT is derived.After analyzing the admittance equation,it is found that the PZT admittance is only related to the mechanical impedance of the measuring point under the condition that the and the angular frequency of the excitation voltage of the piezoelectric coupling system remain unchanged.(2)The PZT admittance is decoupled by the piezoelectric coupling technique.The static part of the PZT admittance is eliminated,and the mechanical impedance of the measuring point is obtained by the remaining dynamic part.(3)The PZT-nut coupling model is established.And when the bolt is preloaded,the state of the nut of bolt is simulated.The development of the real part of the PZT admittance of the nut under different preload is obtained.According to the analysis of damage index,it is found that the change of the admittance real part of PZT is related to the preload force of the nut.The simulation results prove the feasibility of monitoring the looseness of the bolt by sticking the PZT on the nut surface,this laid the foundation for the analysis of the experiment.(4)Under different preload,the PZT admittance real part signal of the nut is monitored,and the state of the bolt looseness is analyzed according to the damage index.Experimental results show that the change of the PZT admittance real part signal is related to the pretension force of bolt.And after decoupling PZT admittance real part signal is realted to the pretension force of bolt.And after decoupling PZT admittance by piezoelectric impedance decoupling technique,the damage index defined by the real part of the mechanical impedance of the measured points hashigher monitoring accuracy.