The failure behavior and the damage zone growth in a glass fiber mat-reinforced thermoplastic polypropylene (GMT-PP) were studied on static tensile loaded single-edge notched (SEN-T) and compact-tension (CT) specimens at room tem perature by using different techniques, such as light microcopy (LM), acoustic emission (AE) and infrared thermography (IT). In the knowledge of the assignation of the AE parameters to the individual failure events the failure sequence was concluded. It was established by AE that the failure mode, and especially the onset of fiber fracture, strongly depends on the fiber content (Vf) of the GMT-PP. This was attributed to an impediment in the mesh-type deformability of the reinforcing mat by increasing Vf. The size of the damage zone was considerably underestimated when deduced from the stress-whitened zone in the LM pictures taken during the loading of the specimens (diameter = 5 mm). Location of the AE by a four sensors array resulted in much higher values (diameter ~ 30mm) being practically unaffected by Vf in the studied range (Vf ~ 20 to 30 vol.%). The damage zone size derived from IT layed between those of LM and AE (diameter ~ 11-16 mm). The occurrence of such a large damage zone clearly demon strates that reliable mechanical data on GMTs can be determined only by using specimens of adequate size (width). It was assumed that the whole damage zone (encompassing a process and a dissipation part) is assessed by AE during the whole fracture process, whereas LM and IT reflect mostly its process zone constituent in the crack initiation and propagation stages, respectively.
The fracture mechanical response of a glass fiber (GF) mat-reinforced polypropylene (GMT-PP) was studied by instrumented Charpy impact testing. The GMT- PP was produced by hot pressing a needle-punched composite textile preform consisting of non-woven PP and continuous GF swirl mat layers. It was established that fracture mechanical values strongly depend on the width of the specimens. The free ligament width of the Charpy specimens (W-a, where W is the specimen width and a is the notch length) should exceed ca. 15 mm due to the inherent material flaw and the large damage zone de veloped. For the size of the inherent flaw, caused by the local arrangement of the GF-mat and its dislodgement due to machining, ca. 2 mm was deduced. This inherent flaw size should be considered when dynamic fracture toughness ( Kd) and initiation fracture energy (Gd,1) values are calculated. It was shown that Kd was unaffected, whereas Gd,1 decreased with increasing fiber fraction (Vf) in the range of Vf ~ 0.2 to 0.3. Contrary, the ductility index (DI), indicating the energy absorption ratio in the crack propagation stage, and the overall impact resistance increased with V f. The pressing conditions (temperature in the range of 190 to 200°C and pressure from 4 to 6 MPa) of the textile preform did not affect the fracture mechanical data which showed always a big scatter.
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