1.School Institute for Advanced Communication and Data Science, School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China 2.School of Mechatronic and Automation Engineering, Shanghai University, Shanghai 200444, China 3.School of Mechanical Engineering, Shanghai Dianji University, Shanghai 201306, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 11874255, 11904223)
Received Date:07 January 2021
Accepted Date:08 February 2021
Available Online:09 June 2021
Published Online:05 June 2021
Abstract: Carbon-fiber-reinforced-polymer (CFRP) composites are widely used in aerospace, automobile and other industries because of their excellent performances. However, wrinkles will be formed during the manufacturing and service life process of composites, which is detrimental to the fatigue limit and tensile strength. Due to the fiber waviness, the presence of such defects leads to the acoustic energy difference in different beam directions during ultrasonic nondestructive testing. The directly obtained imaging amplitude cannot characterize the wrinkle properly. In order to solve this problem, the total focusing method (TFM) imaging combing the acoustic beam directivity function correction is presented. Firstly, the longitudinal wave signal is excited by an ultrasonic phased array, from which the echo data is collected by full matrix capture (FMC) in both the healthy and defected samples prepared. Then, considering the difference in acoustic energy from different beam directions of each ultrasonic transmitting/receiving array element, a correction TFM is proposed. Finally, the echo signals are post processed while the results are compared with the optical images. No wrinkle information can be indicated from the direct TFM imaging. In contrast, the wrinkles and layer-up information can be recovered from the corrected TFM imaging with an improved signal-to-noise ratio and resolution. Furthermore, owing to the directivity function, the near-surface noise can be effectively reduced and the near-surface fibrous layer information is restored. This method paves the way for the accurate, quantitative and rapid characterizing of wrinkles in real CFRP structures. Keywords:ultrasonic phased array/ wrinkle defects/ total focus method imaging/ directional correction
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2.1.全聚焦成像原理
全聚焦成像算法是基于全矩阵采集的后处理算法, 图1是其原理图. 利用超声相控阵捕获全矩阵信号, 由N个阵元组成的超声探头依次单独激励阵元发射超声信号, N个阵元同时接收信号, 得到一个N × N的全矩阵信号. 图 1 全聚焦成像算法原理图 Figure1. The schematic diagram of TFM imaging.