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3D printing technologies are widely used in aerospace, automobile, and other fields due to their rapid manufacture of strong and lightweight products without additional molds and components. However, the relatively low mechanical behaviors of 3D printed composites were due to the weak pristine matrix and the inherent porosity of the fused deposition modeling (FDM) technology. This drawback was compensated by the addition of hybrid continuous fibers for improving the comprehensive and designable characteristics. In addition, the properties of the hybrid composites could be influenced by changing the processing parameters. Therefore, this work aims to study the mechanical properties of designed 3D printed hybrid continuous carbon and Kevlar fibers reinforced polyamide (PA)‐based composites with different fiber layer locations and stacking sequences. The quasi‐static indentation (QSI) tests were conducted to evaluate the mechanical behaviors of the printed composites. The deformation and failure mechanisms of the printed composites were revealed by fractography. Results demonstrated that the printed composites with the middle fiber layer locations showed the highest force value (Fmax) and higher energy absorption capabilities than the printed composites with the fiber layers placed in other locations, which was attributed to the delayed cracking propagation and large delamination, respectively.

Fused deposition modeling (FDM) is a promising additive manufacturing technique for fabrication of continuous fiber-reinforced thermoplastic composites. For composite applications, the balance of material properties, including rigidity and toughness, needs to be considered. To overcome the drawbacks induced by single continuous fiber reinforcement, this study focused on the design and characterization of hybrid continuous fiber (continuous carbon and Kevlar fibers)-reinforced polyamide (PA)-based composites, prepared by 3D printing, to achieve comprehensive performance improvements and designable mechanical properties. The deformation and failure behaviors with the effects of hybrid conception, stacking sequences, and raster orientations of composites were investigated. A hybrid effect model was introduced to evaluate the hybrid effect of 3D printed continuous fiber-filled composites. Besides, compared to composites fabricated via conventional methods, a major difference in 3D printed hybrid composites is the performance of interfacial bonding. A roller peeling test was therefore conducted to investigate the interfacial strength of different materials. An analytical approach was developed to predict the tensile modulus of the printed hybrid composites by introducing an interfacial strengthening coefficient into the volume average stiffness model. The combined experimental and predicted results showed that hybrid composite specimens with separated distribution sequence showed a higher tensile modulus compared to hybrid composites with concentrated distribution. The higher tensile properties of the printed hybrid composites with separated continuous fiber-reinforced layers were attributed to the strong interfacial bonding, which delayed crack initiation and propagation. KeywordsFused deposition modeling • Hybrid continuous fiber • Hybrid effect model • Stacking sequence • Raster orientation • Prediction model • Interfacial properties Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.