Mechanical and damage behavior of short and continuous carbon fiber reinforced additively manufactured multiscale composite

In this study, a novel fused filament fabrication (FFF)-based additive manufacturing technique is developed to fabricate carbon fiber-reinforced (CFR) multiscale composites. The multiscale composites are fabricated by embedding macro-scale continuous woven carbon fibers (CCF) between the micro-scale short carbon (SC) fiber reinforced acrylonitrile butadiene styrene (ABS) polymer laminates. An experimental investigation is performed to observe the effect of raster orientations (+45°/-45°, 0°/90°, and 0°) and fiber content on the tensile and flexural properties of the fiber-reinforced multiscale composites. Digital image correlation (DIC) is used to obtain strain components on the surface of the specimens. Multiscale reinforced composites show superior mechanical properties as compared to short fiber reinforced composites. The CFR multiscale composites show 180 % higher ultimate tensile strength and 225 % higher tensile modulus, along with 61 % higher flexural strength and 107 % higher flexural modulus compared to the short carbon fiber-reinforced composite. The full-field strain distribution from DIC analysis shows strain concentration at void-rich regions, leading to transverse matrix cracking and eventual fiber and matrix failure under tensile loading. In contrast, flexural tests reveal tensile and compressive strain zones on the bottom and top parts of the specimen, respectively, with an upward shift of the neutral axis as tensile strain increases. Matrix cracking initiates at the tensile surface and propagates along the fiber-matrix interface, causing interfacial delamination. Morphological analysis identifies fiber breakage and pull-out, matrix failure, and fiber-matrix debonding as the dominant tensile failure loading, whereas flexurally loaded composites experience delamination, laminates buckling, and matrix failure.