Research On Structural Health Monitoring Technology Based On Ultrasonic Phased Array Theory

Active diagnostic Lamb wave method is one of the most effective Structural Health Monitoring (SHM) techniques due to its sensitivity to small defects in plate-like structures. Phased array imaging technology is a new research direction in the Lamb wave structural health monitoring. Phased array structural health monitoring technique uses the ultrasonic phased array transducer to scan the structure of a technology. Lamb wave beam steering is controlled well to the desired directions by controlling the time delays of transmiting and receiveing of each transducer to realize the multi-directional scanning for the structure, to identify the structural damage, and to get the mapped image of the recogzition results. The goal of research in this dissertation is to detect damage information based on active diagnostic Lamb wave and phased array technology. This research lays the foundation for developing SHM system in practical methods.The main works done in this dissertation include:(1) The modeling of PZT actuating, Lamb wave propagation and PZT sensing have been analyzed. On this basis, ultrasonic phased array theory based structural health monitoring is researched. The directivity of Lamb wave and the scanning principle is analysed. The beam-steering of the Lamb wave is controlled to the special direction to scan the structural and the damage is recognized by phased array technology.(2) Phased array theory based structural health monitoring and imaging technology is researched. The phased array imaging technology is proposed for active diagnostic method to clearly descript the damage. And the confirmatory experiment is done. Shannon wavelet and HHT algorithm is researched to calculate the time of arrival of the signal.(3). Improved experiment method of data collection is proposed to shorten the experimental time. Improved experimental menthod of data collection is verified by the experiment in composite structure.(4) Baseline free damage imaging method was researched to improve its practicability. Baseline free damage monitoring method is verified by the experiment in composite structure.(5) Three kinds of image enhancement method are studied and used in the maped image corresponding to the phased array structural health monitoring results to improve the image quality and recognizable degree. The three methods are verified by experiment.(6) Near-field phased array imaging structural health monitoring method is proposed to overcome the monitoring distance limitation of the far-field phased-array method and to improve the accuracy of the monitoring results. The experiments are successfully done in carbon-fiber box to monitor the load in the structure.(7) Application research works of phased array based active diagnosis method are done on the UAV wing box. Simulating damage and screw loosening are well identified by phased array method in the UAV wing box with load-mass.