Research On Aluminum Plate MUSIC Imaging Method By Lamb Waves Based On Compact Transducers Array

With the rapid development of science and technology,aluminum plates have the advantages of low density,good mechanical properties and processability.Aluminum plates have been widely applied in many fields such as aerospace,transportation and so on.However,because the plate for long-term use,some sorts of irreversible damages are produced.These damages shorten the service life of the plate and lead to serious consequences.Therefore,it is particularly important for health monitoring of aluminum plate.As one of efficient non-destructive testing methods,the technique of compact ultrasonic transducers array,has great application potentials in the field of structural health monitoring.Laser ultrasonic technology has the advantages of fast detection speed and high efficiency.It has been widely concerned in the field of nondestructive testing.In this dissertation,based on the technique of compact ultrasonic transducers array,different array forms are combined with piezoelectric ultrasonic technique and laser ultrasonic technique respectively.Meanwhile,different imaging algorithms are introduced to locate defects accurately in aluminum plates.The major research works include:(1)Optimization of array parameters.Firstly,the influence of the element spacing and the element number on the directivity of the array is analyzed by numerical simulation.Subsequently,the influence of the element spacing and the element number on the imaging quality is investigated by array experiments.By the combination of the theoretical and experimental investigation,the optimal array parameters are optimized.(2)Imaging algorithms and pretreatment methods for array signals are proposed.Firstly,the continuous wavelet transform and linear mapping compensation technology are used to process the array signals.Finally,the amplitude imaging algorithm,the sign coherence factor imaging algorithm and the MUSIC imaging algorithm are introduced to detect the defects for different types of arrays.(3)The defect detection based on piezoelectric transducers array technology is investigated.By the combination of piezoelectric ultrasonic technology and compact transducers array technology,the defects at different positions are located and imaged in aluminum plate.(4)The defect detection based on laser ultrasonic transducers array technology is investigated.Based on the principle of two waves mixing interference,the full laser detection system is set up.Based on signal extraction at a certain frequency point and the pretreatment of dispersion removal,the defects are detected and located in aluminum plate with the help of array scanning method.