Defects Detection With The Broadband Excitation In Plates

With large surface coverage property, plate style structures have been widely used in many pivotal fields such as aerospace, wind power, autoumobile. In the process of usage-many kinds of defects will be arised as equipemts aging, eroded and impact. Structural health monitoring (SHM) and nondestructive evaluation (NDE) have great economic and pratical value to keep the integrity and security of infrastructures and facilities. In this paper, using finite element method and experiment methods to analys the defects detection effects of Lamb waves. Chirp signals have broadband in frequency domain have been loaded on circular piezoelectric patches(PZT) as excitation to incentive Lamb waves in the plates. Getting the tone burst simulate results from Chirp responses. The major research works and conclusions are outlined as follows:(1) Analysis the scattering signals of the rectangular and elliptical penetration defects of So mode Lamb waves in aluminium plates that builted with commercial numerical software Abaqus, the chirp signal is used as excitation. Extract the tone burst responses thats have various of center frequencies from the chirp excitation response. Frequency-amplitude sequences that combined with a set of frequencies and the amplitude of the first received wave packet of defects scattering signals are used to indicate defects information. In order to realize defects identification, BP neural networks are used as classifier thats are trained with training samples. Through the trained BP neural networks the kinds and geometry sizes of defects in testing samples are identified successfully.(2) The elliptical imaging algorithm implementation process were detailly described. Realized square penetration defect location that’s sides length are 6 millimeter with the Tone burst responses that calculated from Chirp responses, the tone burst had different center frequencies at 5 cycles. Through the imaging results to find the raltionship between the location accuracy and frequencies.(3) Analysis of the scattering distribution property of a 9 millimeter hole in plates. As the guided wave propagation pathes will be disrupt when there exist a defet in the pathes, analysis the difference between two received signals at symmetrical arranged sensors. Find the subtraction of the received signals contained the scattering signals of the sensors and realize the defect imaging without baseline through numerical model analysis. At the same time point out several points that’s need to be cared in pratical analysis.(4) Analysis of the Lamb wave propagation velocity distribution in 16 layers T300/QY8911 composite laminate with Chirp excitation. Through shadow effect, realized the defect location that is simulated by a 30mm diameter steel column. At the same time, the defect zone were successfully imaged with the relationship between the defect location and the pitch-catch pathes.