Effects of Pre- and Post-Processing on Pin-Bearing Strength of 3D-Printed Composite Specimens with Circular Notches

To apply 3D printing-based continuous fiber composites in shipbuilding and marine applications, the pin-bearing fastening method with notch holes can be considered as an effective method. In this study, pin-bearing strength tests were performed on a 3D-printed composite consisting of carbon fiber and Onyx to evaluate the effect of hole notches fabricated through pre- and post-processing. The experimental results showed the difference in the mechanical fastening strength of the specimens, depending on the method used to fabricate the hole notch. As the width-to-diameter ratio (W/D) decreased, ultimate bearing strength, strain, and toughness decreased. The post-treated specimens exhibited higher initial stiffness than the pre-treated specimens, and their bearing stress was up to 23% higher at smaller hole diameters (≤6 mm). In particular, for specimens with 0° fiber orientation, the post-processed specimens showed markedly higher toughness than the pre-processed ones, with increases at 5 mm and 6 mm hole diameters, respectively, thereby demonstrating superior performance in both strength and energy absorption. The damage modes of the circular notches were also found to depend on the pre- and post-processing conditions. These results suggest that fiber orientation, W/D ratio, and processing method should be considered when designing mechanical fasteners for 3D-printed composites in marine structures.