Fatigue behavior of continuous glass fiber composites: Effect of the matrix nature

The effect of the matrix morphology on the fatigue behavior of a continuous glass fiber/polypropylene (GF/PP) composite system was studied by means of stress-life and mode II cyclic delamination tests. The stress-life behavior of a GF composite is considerably affected by the nature of the matrix. A two-stage fatigue damage curve was observed in the composite made with a PP matrix, whereas a three-stage curve was observed in the composite made with a thermoset polyester matrix. For a fatigue stress higher than 50% of the yield stress, the PP matrix composite shaved a considerably longer fatigue life than the thermoset polyester matrix composite. Mode II cyclic delamination tests showed that the morphology itself of the PP matrix also played an important role. Higher fatigue delamination growth rates, at given strain energy release rates, and lower strain energy release rates at failure were obtained for a composite showing a coarse spherulitic morphology and well-marked interspherulitic regions than for a composite showing a finer spherulitic morphology and less-marked interspherulitic regions. While the fatigue mode of the composite with a coarse spherulitic morphology was interspherulitic, that of the composite with a finer spherulitic morphology was transpherulitic.