FRACTURE-MECHANICAL CHARACTERIZATION AND DAMAGE ZONE DEVELOPMENT IN GLASS-FIBER MAT-REINFORCED THERMOPLASTICS

It was established that reliable fracture mechanical values of glass mat-reinforced thermoplastics (GMT) can be determined only by using specimens of proper dimensions. The free ligament width of the specimens (W-a, where W is the specimen width and a is the notch length) should exceed ca. 15 mm due to the large damage zone developed. The size of the damage zone was determined on modified compact tension (CT) specimens by localizing the acoustic emission (AE) events during loading. The damage zone was strongly underestimated when light microscopic (LM) pictures, taken during the loading of the specimens, were considered. Simultaneous monitoring of the failure by AE and LM allowed to assign the failure events and to assess the failure sequence, as well. It was supposed that the size of the damage zone and thus the load transfer within, strongly depend whether the stress-strain characteristics of the matrix and that of the reinforcing mat are matched or not.