AE Technique for Identification of Micro Failure Modes in CFRP Composites

Abstract

The fundamental characteristics of AE signals, such as the attenuation, frequency dependency of AE signals in CFRP composites, were investigated. The fracture process of the s.f.c. (single fiber composite) was examined. As a result, the frequencies of AE signals were almost unchanged, while AE amplitudes attenuated greatly with the increment of propagation distance. This proves that the frequency analysis is an effective way in processing AE signals of CFRP composites. Using the frequency analysis, the relationships between the micro failure modes and the frequencies at the peaks of the power spectrum distribution were established. In the fracture process of the s.f.c., the sources of AE signals were the failure modes at the fiber breakages. Using the time-frequency method of the short-time Fourier transform to process AE signals in CFRP composites, the micro failure modes at a fiber breakage and the microfracture mechanism, such as the sequence of failure modes and their interaction, were made clearer. It was shown that two processing methods of AE signals, the frequency analysis and the short-time Fourier transform, were powerful to identify the micro failure modes and elucidate the microfracture mechanisms in CFRP composites.