Acoustic emission waveform analysis in CFRP under Mode I test

In this paper the capability of acoustic emission (AE) to monitor delamination in unidirectional CFRP subjected to mode I loading conditions was tested. Double cantilever beams made by epoxy resin reinforced by carbon unidirectional fiber were tested. By following the ASTM D5528-01 standard the laminates have an even number of plies and delamination grows up following the 0° horizontal direction. Specimens were prepared so that an insert was placed in the mid-plane acting as an initiation site for delamination. Test were carried out at room temperature and at constant displacement rate. Delamination evolution was followed in two ways: first of all it was monitored by putting a CCD camera which follows the damage propagation by observing at the sample through a proper reference grid sized by following the indications of the ASTM D5528-01 standard. At the same time a piezoelectric sensor was placed on the top of each specimen and coupled by a silicon gel. The wave-sound generated inside the sample during the test was recorded by the sensor and pre-amplified before being recorded by the PAC-PCI-2 data acquisition system. Main features of the acoustic signals were analyzed such as hits number, energy and amplitude. Moreover, a wavelet analysis on the recorded waveforms was performed in order to find possible correlation between the frequency content of the acoustic signal and the damage evolution.