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 purpose of this thesis is to investigate the appUcability of discrete wavelet transforms in the analysis and time-frequency breakdown of AE signals detected during fatigue loading of FRC materials. The first objective is to decompose the AE signals into different levels based on the central frequency around which the emissions are generated. The second objective is to identify the frequency at which friction based emissions are generated. The final objective is to determine if a possibility exists to associate various failure modes with specific frequencies.