Estimation of porosity content of composite materials by applying discrete wavelet transform to ultrasonic backscattered signal

摘要

As the use of composite materials in the aerospace industry increases, the development of advanced nondestructive evaluation (NDE) techniques for composite materials is in demand. Ultrasonic quantitative NDE technique for composite materials may provide good information on manufacturing quality, material strength and perhaps useful lifetime. It is well known that the effects of porosity in composite laminates on ultrasonic attenuation and velocity can be used in gauging the porosity content in composites, but back surface echoes may be absent or unusable due to complex geometry and bonding effects. In such cases the backscattered signals may be processed to extract porosity information. Measuring the porosity content in composite material by ultrasonic backscattering signal is a significant challenging problem in NDE of composite material. Backscattering signals are random and sensitive to volume fraction of pore and thickness of ply in composite material. Therefore the backscattering signal has various frequency bands and hence a signal decomposition method is required to analyze the ultrasonic backscattering signals. In this study, the discrete wavelet transform (DWT) using a MATLAB decomposition algorithm was applied to ultrasonic backscattered signals acquired in various porous composite laminates containing a porosity content that ranges from 0.01 to 11.90%. The ultrasonic backscattered signals were decomposed into two parts: the high frequency components called "Details" and the low frequency components called "Approximation". And then, the correlation analysis was performed between the porosity content and the peak amplitude and magnitude of peak frequency of the decomposed signal. Overall, the correlation was reasonably good. As a conclusion, the DWT technique showed good benefits for analyzing the porosity content in composites using ultrasonic backscattered signal from composite materials.