| Wind turbines are composed of different structural components and components connected by a certain connection method.Bolt connection is the main connection method for key structures such as towers and blades of wind turbines.Under complex service conditions,structural vibrations are likely to cause bolts to loosen,affecting the overall performance.reliability and safety of machine operation.The ultrasonic guided wave technology uses the influence of the loose state of the bolt connection interface on the ultrasonic guided wave transmission signal to detect the bolt looseness.At present,PZT piezoelectric sheet is usually used as the sensor of ultrasonic guided wave transmission signal.PZT piezoelectric sheet is made of lead zirconate titanate,which is hard,brittle and fragile,and cannot meet the long-term detection of fan structure connecting bolts in harsh field service environments.Require.In this paper,a piezoelectric composite material with good flexibility and excellent sensing performance was prepared by compounding PZT powder and silicone resin polymer,and the influence of different factors on the sensing performance of piezoelectric composite material was explored.The ultrasonic guided wave transmission signal is received on the surface,and the influence of the loosening degree and number of bolts on the ultrasonic guided wave transmission signal is carried out,thereby providing a theoretical basis for the bolt loosening detection.The main research contents of this paper include the following three aspects:(1)Through the contact mechanics analysis of bolted joints under the action of pretightening force,the propagation characteristics of ultrasonic guided waves in the structure are studied,and the principle of ultrasonic guided wave technology to realize bolt loosening detection is explored;the finite element simulation model of bolted joints is established to analyze different Variation of ultrasonic guided wave transmitted wave signal under preload.The results show that as the bolt loosening degree increases,the interface contact area and contact stiffness of the connector decrease,and the first arrival wave amplitude of the ultrasonic guided wave transmission signal decreases.(2)The 0-3 type piezoelectric composites with excellent performance were prepared by compounding PZT and silicone resin,and the two-component mass ratio of PZT and silicone resin,PZT particle size,and polarization electric field on the sensing performance of piezoelectric composites were explored.Influence of parameters,orthogonal experiments were carried out to explore the relationship between the primary and secondary effects of the three on the sensing performance parameters of piezoelectric composites.At 3k V/mm,the piezoelectric voltage constant g33 of the piezoelectric composite reaches 146 m V·N-1,and the dielectric loss is 0.027.The primary and secondary factors affecting the sensing performance are PZT particle size,mass ratio,and polarization electric field.(3)Paste the piezoelectric composite material sensor on the surface of the flange structure to receive the ultrasonic guided wave signal,determine the ultrasonic guided wave excitation signal and the optimal excitation position,change the pre-tightening force of single or multiple flange bolts,and carry out the bolt loosening detection experiment,introduce the bolt loosening coefficient,and obtain the relationship between the loosening degree and the loosening number and the loosening coefficient.The experimental results show that: as the loosening degree of flange bolts increases,the looseness coefficient of ultrasonic guided wave transmission signal decreases;under the same pre-tightening torque,the looseness coefficient of ultrasonic guided wave transmission signal decreases with the increase of the number of loose bolts.,which provides a theoretical basis for flange bolt loosening detection. |
PDF Full Text Request