Optimization Research On Monitoring Method Based On Piezoelectric Ultrasonic Phased Array

Structural health monitoring is increasingly valued with the rapid development of the aerospace craft.Piezoelectric ultrasonic phased array damage monitoring and imaging technology is one of the structural health monitoring methods,which is based on the piezoelectric sensor with dense array and active Lamb wave.This method not only has the feature of being sensitive with small damage of structure,but also has the advantages of controlling beam pointing flexibly and realizing scanning structure,which has become a hot research topic around the globe in recent years.This paper studies the optimization method for the problems,such as the blind angle,the phantom image,the near-field blind angle and the Lamb wave dispersion compensation,which are appeared in applications of piezoelectric ultrasonic phased array structure health monitoring method.The effectiveness of the optimization algorithm is proved through systemically experiment.The main researches of this thesis are as follows:(1)To deal with the problems that the linear ultrasonic phased array cannot cover the whole azimuth angular system and the phantom image,the omni-directional damage detection and localization method is presented with a cruciform ultrasonic phased array and ultrasonic phased array imaging technology.The method through the fusion of damage scattering signals received by two one-dimensional linear array with delay-and-sum,effectively makes up for the perspective of a single linear array blind area problem,by superposition of the energy of injury signal to suppress false like problems,the accurate detection for single or multiple damages in full angle mode of structure is realized.(2)Aiming at the problem of near field blind area and the low positioning accuracy in ultrasonic phased array damage monitoring,a near-field comprehensive damage ultrasonic phased array imaging method is proposed based on triangle localization algorithm of near field damage monitoring and the cruciform ultrasonic phased array.This method can effectively solve the problem of near field blind area and angle blind area,and also can realize high precision imaging omni-directional damage detection and localization.The method has been verified by the experiment.(3)Aiming at the problem that it is difficult to detect the multiple damages close to each other effectively due to Lamb wave dispersion characteristic,the piezoelectric ultrasonic phased array multiple damages monitoring method is proposed based on measured curve of wave number and frequency dispersive compensation algorithm.Making frequency dispersive compensation to the damage scattering signals by measuring curve of wave number and linearization transformation,effective localization of multiple damages close to each other is achived.(4)Near-field and all aspect ultrasonic phased array damage imaging with carbon fibre composite fuselage skin of real aircraft fuel tank is studied.Based on the method proposed in this thesis,effective localization and imaging for composite fuselage skin damage with variable thickness is realized.