COMPARISON OF THE FAILURE MODE IN SHORT AND LONG GLASS-FIBER-REINFORCED INJECTION-MOLDED POLYPROPYLENE COMPOSITES BY ACOUSTIC-EMISSION

The failure mode in injection-molded short (SGF) and long glass fiber (LGF) reinforced polypropylene (PP) was studied on compact tension (CT) specimens simultaneously by acoustic emission (AE) and transmitted light microscopy. A significant difference was revealed in the failure manner characterized by the cumulative run, amplitude and energy distribution curves between the SGF- and LGF-PP both in the crack initiation and propagation stage. It was established that the failure of SGF-PP did not alter with the loading; this composite failed mostly by matrix deformation along with fiber/matrix debonding and some fiber pull-out. The failure mode of the LGF-PP differed from that scenario, since fiber fracture was resolved in every stage of the loading. On the contrary to SGF-PP, the failure of this composite was governed by fiber-related events (fracture, pull-out, debonding). The amplitude and energy of the AE signals were assigned to individual failure events and thus the failure sequence concluded.