Fatigue behaviour of tailored blank thermoplastic composites with internal ply-drops

摘要

The technology of tailored blanks is used for thickness variation within a laminate plate to reduce weight in areas with lower loading. Ply-drops are used for the thickness variation and their effect on fatigue characteristics has not yet been investigated for the thermoplastic matrix. This paper describes experimental investigation of asymmetrically tapered carbon fibre-reinforced thermoplastic specimens cyclically loaded in tension. The specimens were manufactured according to design features of a rib demonstrator used in an aerospace structure. Two alternatives of transitions were investigated: single taper from 16 to 11 layers and double taper from 16 to 13 and then from 13 to 11 layers. The two taper alternative significantly improved the fatigue life. Furthermore, the effect of specimen edge quality (abrasive waterjet cutting and milling) caused the change of fatigue life by 25%. In case of the run-out specimens with more than 3 million cycles, an early failure occurred at higher load levels due to damage accumulation. Fractographic examination using scanning electron microscopy confirmed occurrence of various features typical for two observed failure modes. It was shown that laminate edges of ply-drop integrated structures should be machined precisely in order to maintain their durability.