FRACTURE-MECHANICAL CHARACTERIZATION OF A GLASS-FIBER MAT-REINFORCED POLYPROPYLENE BY INSTRUMENTED IMPACT BENDING

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 developed. 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 (K-d) and initiation fracture energy (G(d,i)) values are calculated. It was shown that K-d was unaffected, whereas G(d,i) decreased with increasing fiber fraction (V-f) in the range of V-f approximate to 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 degrees 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.