Effect of geometric configurations and heat treatment on the tensile properties, joint performance, and failure behavior of 3D-Printed carbon and glass fiber composites

Abstract

This study presents an in-depth investigation into the influence of geometric configuration on the tensile performance, failure behavior of open hole (OH) and bolted joints (BJ) 3D-printed continuous carbon fiber (CF) and glass fiber (GF) composites with heat treatment (HT) and without heat treatment (WHT). Specimens were fabricated with a predefined [90/45/0/−45]2s stacking sequence, incorporating precise hole formation during the printing process. Tensile tests were conducted on unnotched (UN), OH, and BJ specimens with varying width-to-diameter (W/D) ratios (2, 3, and 4). Results show that tensile performance is strongly affected by W/D ratios. As W/D decreased, earlier failure was observed, yet both composites exhibited remarkable notch-insensitivity. GF composites outperformed CF, retaining 70–76 % of strength compared to CF's 49–55 %, due to their superior ductility and stress redistribution near the hole edge. Failure in OH specimens was dominated by transverse and shear-matrix cracking at the hole edge. Bolted joints load-bearing capacity enhanced with HT, enhancing up to 30 % in GF composites. Bearing strength increased with increasing W/D, reaching up to 489 MPa for GF composites and 453 MPa for CF composites with HT. At higher W/D, bearing failure dominated, promoting higher displacement and delayed catastrophic failure, while lower W/D led to net tension failure. Bolted-joint efficiency (BJE) exceeded 250 % in BJ/OH with HT, highlighting the bolt's critical role in stress redistribution. These findings establish the mechanical reliability and design advantages of 3D-printed CF and GF composites for high-performance structural applications requiring robust joint performance and enhanced durability.