Discrete-wavelet analysis of acoustic emissions during fatigue loading of carbon fiber reinforced composites

Wavelet transform decomposition was used to gather time-frequency-based inf ormation from acoustic emission signals generated during fatigue loading of unidirectional Carbon Fiber Reinforced Composite (FRC). The acoustic emiss ions were detected using a resonant sensor and were digitized for analysis. The sensor response was de-convolved from the acquired signal using a poin t-by-point divisional spectral method. The analysis of the collected signal s revealed that friction-related emissions due to the fretting of fractured surfaces are of very high frequency and can mask emissions due to actual d amage. Through utilization of wavelet transforms, it became possible to present th e spectral composition of a transient signal (AK signal) in a time-frequenc y map which is not easily achieved through conventional spectral analysis t echniques. It was determined that most of the acoustic energy (95%) was loc alized in levels corresponding to central frequencies of 120, 250, and 310 kHz. Results indicate friction-related emissions are associated with levels 8 and 9 and have a frequency range of 250-300 kHz. There are indications t hat matrix related emissions are of high frequency and high acoustic energy . The results indicate that wavelet analysis would be an effective tool in the analysis of AE by providing information relative to the frequency of th e emissions.