Flexural behavior and failure mechanisms of multi-material fused filament fabrication beams: Experimental, microstructural, and numerical analysis

This study investigates the flexural behavior and failure mechanisms of fused filament fabrication (FFF) beams manufactured from pure ABS, pure PLA, and three-layer hybrid configurations (ABS/PLA/ABS and PLA/ABS/PLA). Three-point bending tests were conducted to obtain force–deflection and corresponding stress–strain responses, followed by scanning electron microscopy (SEM) analysis of fracture surfaces to elucidate the governing microstructural damage mechanisms. The results indicate that pure PLA specimens exhibit the highest flexural stiffness and peak load capacity but fail in a predominantly brittle manner, whereas pure ABS specimens display enhanced ductility and deformation capacity at the expense of reduced strength. The multilayer beams exhibited mechanical responses intermediate between those of the monolithic PLA and ABS specimens, with their performance strongly influenced by the stacking sequence. The PLA/ABS/PLA configuration exhibited higher load-bearing capacity, which can be associated with the presence of the stiffer PLA outer layers, while the central ABS material region contributed to a more gradual deformation response. In contrast, the ABS/PLA/ABS configuration showed lower load-bearing capacity but greater deformation before final failure, consistent with the more ductile behavior of the ABS outer layers. SEM observations revealed that failure in multilayer specimens is governed by interfacial debonding, porosity, and void formation, whereas interlayer voids and filament necking dominate fracture in monolithic materials. Finite element analysis (FEA) performed in ANSYS accurately captured the experimental load–deflection trends and stress distributions, showing strong agreement with the measured results. The combined experimental, microstructural, and numerical evaluations demonstrate that tailored multilayer material constructions can efficiently balance strength and ductility in FFF-printed structures.