Application of Acoustic Emission Analysis for Damage Investigations in Fibre and Textile Reinforced Composites

For the verification of pertinent failure and damage models of fibre and textile reinforced composites a clear identification of the particular damage entities is an essential premise. In such fibrous composites, the characteristic failure mechanisms are initiated on the microscale and result in a spontaneous release of elastic energy in terms of mechanical stress waves, the so-called acoustic emissions. Therefore, the acoustic emission analysis represents an excellent potentiality for the online detection of the damage progression in fibre and textile reinforced composite structures. Differently structured multilayered symmetric crossply and angle-ply laminates, for whose manufacture different textile fabrics have been applied, were used for the analysis of the successive damage behaviour in thermosetting and thermoplastic fibrous composites. On the basis of extensive experimental preliminary investigations, a systematic optimisation of acoustic emission testing was accomplished. In this context, investigations were realised amongst others in regard to the minimisation of background noises, the effect of strain rate on the acoustic emission behaviour as well as the existence of the KAISER effect. Furthermore, the transfer behaviour of several components of the acoustic emission measurement chain was analysed via face-to-face technique. Due to the detected acoustic emissions, the gradual damage behaviour of the researched laminates could be classified regarding its acoustic activity and intensity into an elementary model with five characteristic damage phases.