Research On Damage Detection In Complex Plates Based On Ultrasonic Guided Wave

Plate structure is the most basic and important part of ship and marine engineering equipment,it includes some complex structures,such as hyperbolic plates,stiffened plates,etc.These complex plate structures are generally formed from flat plates through welding,riveting,or bending processes.Therefore,the connecting parts are prone to damage,which threatens the safe and stable operation of engineering equipment,so it's very important for us to monitor the structural health of complex plate structures.In this paper,non-destructive testing technology based on ultrasonic guided waves is used to study the damage identification of complex plate structures.First,derived the basic propagation theory of the two guided wave modes of Lamb wave and SH wave in a flat plate,and solved the respective dispersion equations by numerical methods;Then,accorded to the dispersion characteristics of the two guided wave modes,the tomography algorithm and the discrete ellipse algorithm are selected for research.And for the irregular plate structure,the RAPID algorithm is improved by defining the three-dimensional weight R',so that it can realize the damage location imaging of the irregular plate structure.Secondly,combined with the finite element method,numerical simulation of ultrasonic Lamb wave propagation in different waveguides.Through the comparative analysis of the propagation forms in the flat and curved plates,the similarity between the circumferential Lamb wave mode in the curved plate and the Lamb wave in the flat plate is verified.And use the improved RAPID algorithm to image the damage location of the hyperbolic plate structure;At the same time,the ultrasonic SH wave was successfully excited in the flat structure by applying displacement loads in different directions,and the fundamental frequency mode of the SH wave was obtained.Finally,designed the damage identification experiments for the hyperbolic aluminum plate and the stiffened plate: Used the ultrasonic damage detection technology based on Lamb waves to conduct damage identification research on the structural defects of welded hyperbolic aluminum plates,in addition,PZT piezoelectric transducers are used to form a sensor network,a single damage is imaged in three dimensions,and proposed a fusion damage probability index I' to characterize the degree of damage;Use ultrasonic SH waves to identify the damage at the joint of the stiffened aluminum plate,a new type of thickness shear(d15)piezoelectric transducer is used to form the sensor network.The discrete ellipse algorithm is used to study the single damage,multiple damage and the degree of damage at the connection,it proved the effectiveness of this technology in identifying damage for the welded structure of stiffened plates.