Abstract
Fatigue crack propagation (
FCP) measurements have been carried out on injection-moulded composites of polyamide 6.6 (
PA 6.6) reinforced with chopped short and long glass fibres (
SGF and
LGF, respectively). Failure mechanisms during fatigue were studied using scanning electron microscopy. Threshold stress intensity factors (
ΔK) at the start of
FCP gave a ranking:
matrix <
SGF composites <
LGF composites
. The observed increase in matrix ductility of the neat resin and the
SGF composites with increasing
ΔK was attributed to a hysteretic heating at the crack tip, the effect of which is reduced by increased fibre loading. LGF composites exhibited a slight higher
FCP resistance than
SGF versions. Failure modes for the
SGF and
LGF composites are suggested and depicted schematically.