Abstract
Injection-moulding induced skin-core morphology related fatigue crack propagation of polypropylene homopolymer was studied for compact tension specimens in tension-tension mode. The microstructure, consisting of 6 zones which were grouped in skin, shear and core layers, was determined by light microscopy. The fatigue crack propagation response in the accelerated crack propagation range can adequately be described by the Paris equation. Onset of stable crack propagation acceleration occurred above a characteristics threshold stress intensity factor (
ΔK
t) which separates the accelerated from that of the delayed stable crack growth region. Measurements carried out on differently cracked compact tension specimens clearly indicated the self-reinforcing effect of the processing induced layer structure. Failure processes were studied by scanning electron microscopy. The shear region was the failure initiation site.