PSI - Issue 77

Jiongyi Yan et al. / Procedia Structural Integrity 77 (2026) 135–142 J. Yan/ Structural Integrity Procedia 00 (2026) 000–000

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increased with turning angles by 42% and peaked at 120° (~0.23), probably caused by over-extrusion and shear gradient. These results agreed with the literature (Yan et al., 2023c), where fibre orientation decreased at corners. At the corners, the internal nozzle pressure spikes, and the outer radius of the extrudate is stretched with lower nozzle shear. This may lead to the over-extrusion on the outer radius where the pressure gradient favours and fibre misalignment without sufficient nozzle shear (Mollah et al., 2022). This enables fibres that are short enough to splay out into the interlayer direction before the melt solidifies. As the turning angle increased, more overlapped over extruded areas occurred at the corners and facilitated fibre misalignment. The slight decrease of 33 for the 150° corner compared to 120° corner may suggest that very sharp turns may induce high shear in the new direction, crushing on the already deposited layer before turning and squeezed the newly deposited layer flat. This could benefit in-plane fibre orientation in the new direction after the turn.

200 μ m

Fig. 1. Measured 3D fibre orientation at corners and micrographs of 3D printed corners with different turning angles.

3.2. Static tensile properties of angular corners For the tensile test, specimens with smaller turning angles behaved in a brittle manner, closer to the regular 3D printed rectangular specimens (Fig. 2a). The force decreased with increased turning angles (by 86.7% from 30° to 150°), while the displacement at break increased from 1.8±0.1 mm to 50.0±5.5 mm. All corners were pulled open and straightened, and sharp corners showed structural failure, namely corner opening where the force dropped (~39.5 mm for the 150° corner). The results showed the flexibility of greater angles but limited stiffness to resist the tension, in contrast to high rigidity of smaller angles. As the turn angle increased, the fracture occurred more deviated from the middle of the corner (Fig. 2b). For the 30° corners, the breakage took place at the middle of the corner, while sharp corners (150°) showed that breakage happened and skewed on one side of the corner. This difference suggests that the corner centre is not necessary the weakest point even with the disrupted fibre orientation. Instead, plastic