Failure mechanism and heat treatment effect of 3D-printed bio-inspired helicoidal CF/PEEK composites

Abstract

The bio-inspired helicoidal structure has displayed a unique combination of lightweight, high strength, and high impact resistance. This study presents an experimental and numerical investigation of the failure mechanism and heat treatment effect of 3D-printed helicoidal composites by adopting a helicoidal laminate stacking configuration found in the dactyl club in Homarus americanus. The helicoidal specimens were additively manufactured with short carbon fiber reinforced Polyether ether ketone (PEEK) composites and their mechanical performance was characterized through quasi-static three-point bending. The results showed that the flexural strength, flexural modulus, and absorbed energy of the helicoidal composites with the twisted crack pattern were 6.9%, 23.9%, and 5.9% higher than those of the quasi-isotropic composites with the flat crack pattern. Stress analysis was then carried out to investigate the underlying failure mechanism of helicoidal materials. The stress component of σ33 and σ13 in helicoidal specimens showed a milder distribution than that of quasi-isotropic specimens, which plays a major role in the resulting fracture-resistant behavior. Further results showed that the helicoidal specimens under heat treatment of 250 °C over 6 h achieved 24.9% and 20.9% enhancement in flexural strength and modulus. The cracking surface area was increased with extensive translaminar twisted cracks observed with a scanning electron microscope. Experiment results show that heat treatment can exert a significant influence on the crack path of the CF/PEEK helicoidal specimens. Meanwhile, the increased degree of crystallization and crosslinking at the interface could inhibit the initiation of delamination failure.