Damage Mechanisms in Hemp-Fibre Woven Fabric Composite, and Comparison with Glass-Fibre Composite

This paper deals with hemp-fibre and glass-fibre woven fabric/epoxy composites. The aim is to analyse damage mechanisms in these composites by comparing three different methods: acoustic emission, microscopic observations and stiffness loss measurement. For acoustic emission (AE), an experimental multi-scale analysis was developed in order to identify the different damage mechanisms. Tensile tests were performed on single yarn, neat epoxy resin and composite materials to determine their AE amplitude signatures. A statistical analysis of AE amplitude signals was realised and correlated with microscopic observations. This study has enabled to identify the amplitude and to track, during tensile tests, three types of damage in these composites: matrix cracking, interfacial debonding and reinforcement fracture. It shows the different processes of damage development in natural fibre reinforced composites, in comparison with glass fibre composites. These results were compared to the measured stiffness loss of composites. It allows one to highlight the difficulty to link this mechanical damage parameter with physical AE events.