Wavelet transform of acoustic emission signals in failure of model composites

The fundamental characteristics of acoustic emission (AE) signals, such as the attenuation, and frequency dependency of AE signals, were investigated and the fracture process of the single fiber composite (s.f.c.) was examined. As a result, the frequencies of AE signals were almost unchanged, while the amplitudes attenuated greatly with the increment of the propagation length. This proved that the frequency analysis is an effective way in processing AE signals of composite materials. In the fracture process of the s.f.c., the number of AE events was in a good agreement with the number of fiber breakages, and the sources of AE signals were the failure modes at fiber breakages. Using the proposed time–frequency method of wavelet transform (WT) to process AE signals, the microfailure modes at a fiber breakage and the microfracture mechanism, such as the sequence of each failure mode and their interaction, were made clearer. These indicated that both processing methods of AE signals, fast-Fourier transform and WT, were powerful for identifying the microfailure modes and for elucidating the microfracture mechanisms in composite materials.