Discrete Wavelet Analysis of Acoustic Emissions During Fatigue Loading of Carbon Fiber Reinforced Composites

Acoustic Emissions (AE) are generated during operational loading of Fiber Reinforced Composite (FRC) materials due to various sources of fracture. These sources which include matrix fracture, fiber fracture, splitting and delamination could be generated individually or simultaneously. The multiplicity of defects and failure modes creates problems in identifying and distinguishing various sources of emissions. This analysis is further complicated due to the friction related emissions (generated during grating of newly generated damage surfaces and fretting of broken fibers with matrix) that mask the actual signal and in most cases, exceeds the emissions from actual damage. The objectives of this research was to decompose the AE signals into different levels based on frequency, identify frequency of friction based emissions and to associate various failure modes with specific frequencies. Through utilization of Wavelet transforms, it became possible to present the spectral composition of a transient signal (AE signal) in a time-frequency map. The results indicate that Wavelet analysis would be an effective tool in the analysis of AE by providing information relative to the frequency of the emissions and assist researchers in determining the extent and type of damage during online inspection of component.