Fracture toughness of additively manufactured carbon fiber reinforced composites

By E. A. Papon, A. Haque. Additive Manufacturing, 2019

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Abstract The fracture properties (stress intensity factor and energy release rate) of additively manufactured (AM) polylactic acid (PLA) and its short carbon fiber (CF) reinforced composites have been studied. The effects of CF reinforcement, nozzle geometry and bead lay-up orientations in fracture properties, void contents, and interfacial bonding were investigated. The fused filament fabrication (FFF)-based AM specimens using both circular and square shaped nozzle were printed and compared with the conventional compression molded (CM) samples. Compact tension (CT) specimens with different CF concentrations (0 wt.%, 3 wt. %, 5 wt.%, 7 wt.% and 10 wt.%) were printed with two bead lay-up orientations ( 45 0 / - 45 0 and 0 0 / 90 0 ) using PLA and CF/PLA composite filaments. The results show significant improvement in fracture toughness and fracture energy for CF/PLA composites in comparison to neat PLA. The fracture toughness was increased by 42% for 0 0 / 90 0 and 38% for 45 0 / - 45 0 bead orientations, respectively with 5% CF loading. The increase in fracture energy was observed to be about 77% for 0 0 / 90 0 and 88% for 45 0 / - 45 0 bead orientations, respectively for the same fiber reinforcement (5 wt. %). Such improvement in fracture properties is expected to be higher for all 90 0 bead orientations. The samples printed by square-shaped nozzle showed enhanced fracture toughness with less inter-bead voids and larger bonded areas in comparison to the circular-shaped nozzle. Although the fracture toughness showed very negligible differences between 0 0 / 90 0 and 45 0 / - 45 0 specimens, distinguishable variation may be seen in the case of 0 0 and 90 0 bead orientations. The crack propagation path and fracture mechanisms were studied using optical microscopy (OM) and scanning electron microscopy (SEM) examinations. Fractography revealed different modes of failure with a very high fiber orientation along the printing direction and a relatively higher void contents for 7 and 10 wt. % fiber reinforcement.

Subfields: Automotive Engineering, Biomedical Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/ea2c958a1c1ae694af93dda3faf6579177ec7488