On the role of the spherulitic microstructure in fatigue damage of pure polymer and glass-fiber reinforced semi-crystalline polyamide 6.6

•Fatigue damage progresses in the polymer by opening each spherulite in its equatorial plane.•Half of the spherulite can be observed on each fracture surface, with the nuclei being perfectly visible.•Injection-molding induces an orientation of the spherulitic structure.•Oriented spherulites are intermediate between the usual radial spherulite and the oriented shish-kebab.