In this study, two types of specimens, woven [0, 90]_s and unidirectional [0]_s glass/epoxy composites, were studied. Acoustic emission (AE) monitoring with wavelet-based signal processing technique and Fuzzy C-Means (FCM) clustering method was used to detect the different fracture mechanisms during delamination in quasi-static three-point bending test. The three-point bending test simulates thrust force, the most effective factor in delamination, throughout the process of drilling without backup plate. The obtained AE signals were decomposed into various wavelet levels and classified using FCM. Scanning Electron Microscopy (SEM) observation was used to determine the different fracture mechanisms. The results show that the energy of AE signals has been concentrated in two significant components for both types of specimens, and the dependency percentage of damages in the two specimens is different.

In this study acoustic emission monitoring was used for detection and classification of damage mechanisms during mode I delamination test of glass/polyester composites. For this purpose, the integration of harmony search and k-means algorithms was applied to cluster acoustic signals generated during delamination test. The clustering analysis represented three clusters, each one related to a distinct damage mechanism. Considering the relationship between acoustic emission parameters and damage mechanisms, the acoustic emission signals of each cluster were assigned to a distinct damage mode. Furthermore, the dominance of various damage types was investigated based on the distribution of signals in different clusters. Finally, scanning electron microscopic observation was employed to verify the obtained results. The results indicate good performance of proposed algorithms in damage classification procedure.

Control and optimization of machining processes are important issues affecting the development of productivity. Monitoring systems have become indispensable in the evaluation of materials during machining. In this paper, the path toward the delamination-free drilling of glass/epoxy composite material is established using some novel methods based on acoustic emission features. Acoustic emission monitoring with three techniques, sentry function, acoustic emission energy distribution, and acoustic emission count distribution, are developed to detect and realize the critical force at the onset of delamination process on glass/epoxy composite materials. The three-point bending test simulates thrust force, the most effective factor in delamination, throughout the process of drilling without backup plate. Sentry function is regarded as a new method based on the combination of AE information and mechanical behavior of composite materials. The sentry function was used to study the initiation and growth of delamination process. Two types of specimen with different layups, woven [0, 90]_s and unidirectional [0]_s, leading to different levels of damage evolution, were studied. Results show that AE parameters and sentry function method are useful tools for the examination of initiation and the growth of delamination during drilling process and can help to avoid delamination damage while drilling.