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.
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