Characterization of the damage process in short-fibre/thermoplastic composites by acoustic emission

Fracture processes of short glass fibre-reinforced thermoplastic tensile sp ecimens have been investigated in relation to acoustic emission (AE) charac teristics. Two fibre diameters (d = 10, 23 mu m) were adopted for this stud y. Frequency analysis employing band-pass filters suggested that AE with hi gher amplitude was due to fibre breakages. Fibre-matrix interfacial failure and matrix fracture emitted lower amplitude AE waves. Reflected-and transm itted optical microscopy, in combination with scanning electron microscopy, revealed that fibre breakage ahead of the artificial notch tip led to the initiation of a macroscopic fracture. This ;coincided with the results that AE peak amplitudes, V-p, showed a minimum at fracture initiation. When the macroscopic fracture propagated, V-p again increased rapidly, indicating a dditional fibre breakage. These fracture mechanism worked consistently for both d = 10 and 23 mu m Based on the above findings, AE source characteriza tion was proposed for the stable fracture process of short fibre-reinforced plastics. (C) 1998 Chapman & Hall.