| Aiming at the loosening of bolts in engineering practice,the method of frequency shift of piezoelectric impedance is applied to the monitoring of axial force of bolts,and the effectiveness of the stress monitoring of the structure is analyzed in one-dimension structure by using the method of the theoretical analysis,the finite element simulation and the experimental research.In addition,an in-depth experimental study based on the method of stress monitoring are conducted on the axial force monitoring of the bolt.The work done in this paper and the conclusions it draws mainly include the following points:(1)Based on the derivation of the piezoelectric admittance formula and the wave theory of the axial-loaded one-dimensional beam,and the quantitative analysis of the influence of the axial force of the host structure on natural frequency of the host structure and the piezoelectric materials,it is concluded that the natural frequency at the transverse vibration of the host structure and the piezoelectric materials will be enlarged by the axial tensile force of the host structure,and reduced by the axial compressed force of the host structure.(2)The finite element software is used to simulate the trend of the modal analysis and the piezoelectric admittance signal when the host structure is subjected to different axial loads,to acquire the relationship between the characteristic frequency at the resonances of the host structure or the pzt patch and the structural stress.(3)With the help of the theoretical analysis and the finite element simulation,in this paper the aluminum plate and the aluminum rods are selected to conduct the corresponding tensile and compressed experiments respectively.The theoretical analysis and experimental results show that,in the piezoelectric admittance signal,the axial tensile load of the host structure causes a linear increase of the characteristic frequency in the resonances of the host structure and the resonances of the piezoelectric material,while the axial compressive load causes a linear decrease.In addition,The monitoring experiment of bolt axial force using this method also verifies the correctness of the above conclusions.Therefore,there is a great potential for monitoring the axial force of bolts based on the characteristic frequency shift of piezoelectric impedance. |
