The ultrasonic evaluation method for the porosity of variable-thickness curved CFRP workpiece: using a numerical wavelet transform

The porosity of variable-thickness curved carbon fibre-reinforced plastic specimens was studied by ultrasonic pulse-echo method. There were six specimens used in the experiment. The thickness of each specimen ranges from 5 to 10 mm and the porosity of the specimens ranges from 0.4% to 3.8%. The backscattered signal was extracted from the ultrasonic signal. Then, the detail decomposed signal, which contains the information of porosity and was obtained from the backscattered signal by lifting wavelet transform, was analysed. The results are as follows. For the original backscattered signal, as the porosity increases, the amplitudes of the signal and its spectrum have a fluctuant increasing trend. The signal energy also has a similar trend. But for the decomposed signal, with the porosity increasing, the amplitudes of the signal and its spectrum have a linear increasing trend. The signal energy increases monotonically and has a quadratic relationship with porosity. By removing the interferential signal with lifting wavelet transform method, the decomposed signal can reflect the porosity information of the material accurately.