Anisotropic and elastoplastic mode-I fracture toughnesses of three additively manufactured polymers fabricated via material extrusion and powder bed fusion

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. 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