Fatigue crack growth and fracture in glass sphere-filled nylon 6

The common degrading effect of glass beads on the static fracture energy and the fatigue crack propagation response in nylon 6 materials is examined by conducting fracture mechanics tests and by considering the progress of cracks through the composites. The scanning electron micrographs indicate that the cracks travel through regions of polymer matrix and also along the interfaces between polymer and glass beads. It is demonstrated that, although fracture of the polymer regions requires considerable energy, cracking of the interfaces usually absorbs very little. Thus, the crack propagation is preferably concentrated on these microstructural regions, which is the cause of the decrease in fracture energy and increase in fatigue crack growth rate with increasing amount of glass spheres in the composite. Partial properties of the matrix and the interface are introduced in order to describe the fracture behavior and to improve the understanding of the gross fracture processes. The combination of these partial properties with the volume fraction of filler and certain geometrical factors by a modified rule of mixture leads to critical values for the failure of the composites, which are in reasonable accord with the measured fatigue and fracture data.