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Two types of additive manufacturing (AM) techniques, fused filament fabrication (FFF) and selective laser sintering (SLS), were employed to fabricate specimens from three widely used AM polymers: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyamide (PA): the first two using FFF and PA using SLS. The single‐edge notch bending (SENB) test was employed to measure the mode‐I fracture toughnesses of bulk and AM specimens in three directions relative to the printing direction. Unlike their bulk counterparts, AM polymers exhibited anisotropic fracture toughness. The degree of anisotropy in FFF‐PLA was much larger than FFF‐ABS and SLS‐PA. The smallest fracture toughness value for each AM polymer was achieved along the transverse printing direction. Different AM techniques affect fracture toughness differently. For instance, FFF is shown to increase PLA's plastic deformation, while SLS reduces PA's ductility. The decrease in fracture toughness is consistently observed when transitioning from bulk polymers to AM ones, reaching as much as 75%. This study provides insights into the fracture toughness of AM parts made via popular plastics, which are crucial for designing structural parts using FFF and SLS processes. Highlights: Additively manufactured polymers always exhibit some anisotropic fracture toughnessDifferent additive manufacturing techniques affect the fracture toughness differentlyFused filament fabrication increases polylactic acid's plastic deformationBut selective laser sintering reduces polyamide's ductility [ABSTRACT FROM AUTHOR]

• Commonly used Tsai-Hill strength criterion mainly predicted the yield strength. • Suggested quadratic strength criterion provided a lower bound of the ultimate strength. • These results were verified by anisotropic ultimate strengths of major 3D printing metals. 3D printing metals have an intrinsic building orientation, so they have some anisotropy in their strength due to the failure between the printing layers with direction dependence that was commonly seen in composite materials. Although the Tsai-Hill composite strength criterion predicted the ultimate strengths of some 3D printing metals made with selective laser melting and laser powder bed fusion (SLM/LPBF), the current study showed that the composite strength criterion was not applicable to the ultimate strength predictions of all 3D printing metals. Our suggested quadratic strength criterion without stress interaction provided conservative strength predictions to ensure safe 3D printing metal applications. Moreover, the shear strength plays a critical role in strength predictions and should be measured accurately. [ABSTRACT FROM AUTHOR]