Fatigue resistance of continuous glass fiber/polypropylene composites: consolidation dependence

The effect of consolidation on the fatigue resistance of continuous glass fiber/polypropylene (CGF/PP) composites was studied. Five sets of conditions, chosen to approach plant-like processing conditions, were used to obtain samples with varying consolidation quality. These conditions resulted in different void content, degree of crystallinity, size of crystalline entities (spherulites) and level of fiber dispersion. Although they led to different short-term (flexural, tensile or short-beam shear) mechanical results, a single linear correlation could be established between the interlaminar shear strength (ISS) and the void content for all consolidation conditions except one. The fatigue resistance of the CGF/PP composites showed that these consolidation conditions also resulted in different fatigue damage evolution and fatigue resistance curves (or S–N curves). From the S–N curves, two useful correlations could be established: the first is a linear correlation between the Basquinʹs fatigue strength and the short-term flexural strength; the second is a linear correlation between the Basquinʹs fatigue sensitivity and ISS. The results emphasize the predominance of the fiber–matrix interface in determining the general mechanical properties of continuous fiber composites and suggest that short-term flexural and short-beam shear tests can be useful empirical indicators of the long-term performance of CGF/PP composites.