Damage evaluation of composite materials using acoustic emission features and Hilbert transform

Acoustic emission (AE) has good potential to characterize failure mechanisms in laminated composite materials. One of the difficult issues using this method can be to establish a good correlation between occurred failure mechanisms and resultant acoustic emission features. Therefore, the aim of this paper was to use a novel method called Hilbert transform to correlate acoustic emission signals to their corresponding failure mechanisms. The investigated acoustic emission signals were obtained from glass/epoxy laminated composites subjected to end notch flexure test which simulates mode II delamination. The phase angle of Hilbert transform was used as a feature to extract the frequency range of damage mechanisms that occurred in different stages of the loading process. The proposed method was used to analyze the extracted acoustic emission signals in three main stages during the loading, i.e. the initiation, the maximum load nearby and the stage where the crack has propagated to the middle of the specimens. A scanning electron microscope was also used to observe the cracked surfaces. The results showed good applicability of the proposed acoustic emission based method for characterization of the damage mechanisms in the laminates. There was also a good agreement between the scanning electron microscopic images and the achieved results.