Adhesively bonded scarf joints in 3D-printed structures under four-point bending

Introduction: Additive manufacturing (AM) enables the fabrication of complex polymer components; however, the limited build volume of most printers often requires joining of printed sub-parts. Materials and methods: This work experimentally and numerically evaluates adhesively bonded scarf joints between fused deposition modelling (FDM) between adherends of polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate glycol-modified (PETG) and two structural adhesives with contrasting ductility: Araldite ® 2015 and Sikaforce ® 7752. The joints were tested under four-point bending (4PB) for overlap lengths ( L O ) of 5, 10, and 20 mm. Peak load ( P m ), maximum stiffness ( k max ), absorbed energy to failure ( E max ), and failure modes were compared with finite element method (FEM) predictions using cohesive zone modelling (CZM). Results: Experimentally, L O = 5 mm led to cohesive failures for all material/adhesive combinations, whereas increasing L O promoted a transition to adherend-controlled failure, particularly for ABS and PETG. P m increased from L O = 5 to 10 mm and then stabilized as adherend failure became dominant, with PLA providing the highest P m . k max was weakly affected by L O , and was consistently higher with Araldite ® 2015 due to its higher modulus. E max increased with L O and was generally higher with Sikaforce ® 7752, reflecting its greater ductility. Conclusions: The numerical model reproduced trends and failure patterns, which supports FEM + CZM as a reliable design tool for AM scarf joints under bending.