Failure mechanisms in composites reinforced with unidirectional Phormium leaf fibre

Confocal microscopy, field-emission SEM and acoustic emission experiments were used to investigate fracture mechanisms in composites made from epoxy resin reinforced with unidirectional Phormium tenax (harakeke) leaf fibre. Resin filled the lumens of a large proportion of thin-walled vascular cells and bundle sheath cells, and also filled some of the fibre cells in assemblies that had been split during fibre processing, but rarely penetrated intact thick-walled fibre cells. Vascular tissue and cuticular matter were particularly susceptible to brittle fracture. Cell–cell debonding was abundant on fracture surfaces. Low-, medium- and high-energy acoustic events showed transient signals of similar duration, constructed from similar frequencies and differing only in amplitude. The wide distribution of event energies was attributed to the diversity of types of technical fibres, from assemblies of a few thin-walled cells to assemblies of hundreds of thick-walled fibre cells.