Clustering effect on damage mechanisms in open-hole laminated carbon/epoxy composite under constant tensile loading rate, using acoustic emission

In the present research, damage mechanisms in the open-hole laminated carbon/epoxy composite have been investigated using the acoustic emission method. For such objective, standard specimens, made of the pure resin, the pure fiber and composites, were tested under tensile conditions, at a constant loading rate. Then, the clustering effect was studied in order to know which damages (debonding, fiber pull-out, delamination, matrix cracking and fiber breakage defects) occurred in the material. For the analysis of acoustic emission signals, wavelet packet transform and fuzzy C-means methods were applied to data. Obtained results indicated that the frequency range for matrix cracking, the fiber breakage, the fiber pull-out, debonding of fibers from the matrix and the delamination was obtained as 100-250 kHz, 420-500 kHz, 250-320 kHz, 320-380 kHz and 380-420 kHz, respectively. Scanning electron microscopy images showed that the dominant damage was qualitatively related to debonding, the fiber pull-out and the delamination, which had a proper agreement with obtained results from the analysis of acoustic emission signals.