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

Abstract

Abstract 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 (ϱ) were nominally zero (0) and 2.3 mm. The larger ϱ 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 ϱ dependence of the damage formation and fracture mechanism of the composite. For ϱ = 0, V p increased drastically and then decreased with increases in load. However, for ϱ = 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 ϱ, 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.