Crashworthiness properties of fused filament fabrication (FFF)-3D printed wood-polylactic acid (wood-PLA) biocomposites depend strongly on their internal architecture, while a systematic multi-criteria assessment of different infill patterns is still lacking. In this study, the crashworthiness performance of tubular wood-PLA biocomposites with eight different infill patterns was experimentally investigated. Six crashworthiness criteria were considered: energy absorption (EA), specific energy absorption (SEA), initial peak force (IPF), mean crushing force (MCF), crushing force efficiency (CFE), and undulation of load-carrying capacity (ULC). The experimental results were evaluated using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Grey Relational Analysis (GRA). The robustness of the obtained rankings was further assessed through sensitivity analysis under different criterion-weighting scenarios. Among the investigated infill patterns, Zig-zag exhibited the highest EA (141 J), MCF (7.05 kN), and CFE (95.2%). Under the baseline equal-weighting condition, Zig-zag achieved the highest ranking in both TOPSIS and GRA, with a closeness coefficient of 0.802 and a grey relational grade of 0.827, respectively. The sensitivity analysis further demonstrated the robustness of the overall ranking, with Zig-zag maintaining the leading position in most weighting scenarios and in all GRA-based scenarios. The proposed experimental-MCDM framework provides an effective approach for the systematic evaluation and selection of infill architectures for lightweight, energy-absorbing FFF-3D printed wood-PLA biocomposites.
