Characteristics of acoustic emission during the damage process in notched short-fibre-reinforced thermoplastics

The effects of the notch tip radius on acoustic emission (AE) characteristics have been studied for short-glass-fibre reinforced poly(ethylene terephthalate) (SGFR-PET) tensile specimens. The adopted notch tip radii () were nominally zero (0) and 2.3 mm. The larger caused an increase in the load corresponding to the beginning of AE and an increase in the maximum load and fracture displacement. AE peak amplitudes (V_p) showed dependence of the damage formation and fracture mechanism of the composite. For = 0, V_p increased drastically and then decreased with increases in load. However, for = 2.3 mm V_p increased fairly monotonically. In a higher amplitude range, V_p exhibited a minimum at the initiation of a main crack for both radii. Frequency analysis suggested that AE sources were not dependent on , and AE events for the higher V_p corresponded to fibre breakages. Reflected and transmitted optical microscopy combined with ultrasonic C-scan revealed that fibre breakages ahead of the notch tip led to initiation of a main crack, which agreed with the results of V_p above. When the main crack propagated, V_p increased rapidly again for both radii, indicating additional fibre breakage. As a consequence, AE characteristics representing the damage formation mechanism in short-fibre-reinforced thermoplastic were found to be considerably influenced by the notch tip radius.