Piezoelectric Active Bolt Loosening Detection Technique Based On Interface Contact State

Bolted structurals are widely used in metallurgical equipment, and their connection statuses(expressed as tightening force) directly decide the reliability and security of the equipment. Boltloosening is not easy to detect, which brings massive destruction, so the bolt preload andreal-time monitoring for its connection status has important applied significance. the ultrasonicmethod is studied using the piezoelectric ceramics with the active sensor technology.Main works and achievements of the thesis are as follows:Firstly, based on Sinusoidal wavy surface model and Hertz contact theory, the model ofultrasonic propagation through contact interface was studied. The relation of the fanctors whichinclude interface roughness, the actual contact area and contact interface stress affecting onultrasonic propagation was obtained. Thus a new bolt axial-force measurement method can be formed.The experimental device is setup and the experiment is carried out. The experimental results show that whenincreasing the torque level for the bolt, more wave energy is received by the sensor.Secondly，Combination of the probability density function and Hertz contact theory. Themicroscopic contact model of the interface of the two parts jointed by the bolt is was studied.using the equivalent stiffness to represent the state of contact of the interface. The relationshipbetween bolt preload, the equivalent stiffness and modal frequencies was obtained. Usingultrasonic measurement tracking the changing mode frequency in preload. Anew bolt axial-forcemeasurement method can be formed. based on the modal frequency tracking. Experimentalresults show that a modal frequency value and applied torque level has a linear relationship.The piezoelectric ceramics with the active sensor technology has practical significance.