Fourier transform has been used to study the frequency characteristics of a signal. However, based on the Fourier transform and power spectrum alone, it is hard to tell whether or not the frequency content of a signal evolves over time, even though the phase of the Fourier transform relates to time shifting. On the other hand, except for a few special cases, the frequency content of the majority of signals encountered in the real world change with time. Recently, to overcome the problem that Fourier transform is unable to represent a nonstationary signal, time-frequency analysis methods that can simultaneously represent information about the time and frequency of a signal have been developed. In this study, the damage process of cross-ply carbon fiber reinforced plastics (CFRP) during a monotonic tensile test was characterized by acoustic emission (AE). Different laminated types of CFRP were used to determine the characteristics of the AE signal and frequency. The time-frequency analysis method was found to be useful for the determination of the fracture mechanism in CFRP (such as, matrix cracking, debonding- delamination, and fiber fracture). (C) 2003 Wiley Periodicals, Inc.
