Fundamental Lamb Mode-based Delamination Detection for CF/EP Composite Laminates Using Distributed Piezoelectrics

Abstract

A delamination detection scheme for the CF/EP composite laminates based on the Lamb wave propagation was proposed. The fundamental symmetric Lamb mode ( S0) and the delaminationinduced basic shear mode ( S’0) in an ultrasonic frequency range were utilised for locating the delamination. Both numerical simulation and experimental studies were performed to evaluate the propagation characteristics of Lamb waves in the composite laminates involving a delamination. An active online damage diagnosis system was established with a transducer network configured using distributed piezoelectrics. Bandpass filters were designed and spectrographic analyses in the time-scale space via wavelet transform technique were accomplished, to diminish diverse broadband interferences and consequently improve signal interpretation. Algorithm based on a graphic approach was introduced into the damage searching procedure to expedite the diagnosis and minimise the estimation errors. The proposed identification scheme and diagnosis system were then validated by detecting delaminations in CF/EP laminates made from unidirectional and woven fabric prepreg, respectively. Satisfactory prediction for the damage location has been achieved. Additionally, the influence of diagnostic waveforms and frequencies on the identification accuracy was also evaluated.