Continuous carbon fiber reinforced thermoplastic composites (CFRTPCs) fabricated by fused deposition modeling (FDM) exhibit strong anisotropic mechanical behavior, making fiber path design critical for structural performance. However, conventional raster-based path planning strategies do not account for stress redistribution in mechanically joined structures, thereby limiting their load-bearing efficiency. This study shows that aligning continuous fiber paths with the principal stress field significantly enhances the mechanical performance of joining hole structures. Under identical loading conditions, an improvement of up to 39% in ultimate load observed while reducing total fiber usage by 4.2%, compared with conventional 45°/135° toolpaths. In addition, the displacement at ultimate load decreased by 9.8%, indicating improved stiffness and load transfer efficiency. The novelty of this work lies in demonstrating that performance enhancement is primarily governed by stress-path alignment and fiber redistribution toward high-stress regions, rather than by increasing fiber quantity. These findings provide experimental evidence for stress-adaptive reinforcement design in continuous fiber 3D printing and suggest practical potential for lightweight load-bearing composite structures.
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