Mechanical performance of bi-adhesive single-lap joints produced by FDM with PLA adherends

Purpose This study aims to investigate the mechanical performance of bi-adhesive single-lap joints fabricated using fused deposition modeling (FDM) with polylactic acid adherends. By combining a brittle and a ductile epoxy adhesive in different sequences and area distributions, this study seeks to determine optimal configurations that enhance joint strength and ductility under tensile loading. Design/methodology/approach In all, 14 different joint configurations were produced by varying adhesive lay-up sequences, adhesive area divisions and bondline orientations (perpendicular and parallel). Samples were manufactured using FDM with polylactic acid material and tested according to ASTM D3163-01 under uniaxial tensile loading. Fracture loads, elongations and failure modes were recorded and statistically analyzed. Findings The mechanical performance of single-lap joints was highly dependent on adhesive sequence, area division and orientation. The highest load-bearing capacity was achieved by the Ductile–Brittle–Ductile configuration with a thick central brittle core under parallel loading, reaching a maximum force of 591.1 N and elongation of 0.461 mm. Under parallel loading, the Brittle–Ductile–Brittle configuration with dominant brittle adhesives performed best with 557.6 N and 0.520 mm elongation. Compared to single-adhesive joints (maximum 366.05 N for ductile adhesive), bi-adhesive configurations improved tensile strength by up to 61.5% and elongation by 47.8%. It was also observed that perpendicular lay-up of ductile adhesives at the joint edges effectively delayed failure and improved energy absorption. Originality/value To the best of authors’ knowledge, this work presents one of the first systematic experimental studies examining the combined effects of adhesive sequencing, area distribution and orientation on the mechanical behavior of bi-adhesive joints produced via FDM. The findings of this study demonstrate that intelligently engineered bi-adhesive arrangements can significantly outperform single-adhesive systems in both strength and ductility, offering valuable insights for the design of high-performance three-dimensional-printed bonded structures in lightweight and load-bearing applications.