Impact response of FFF-printed bio-inspired multi-material helicoidal structures: An experimental investigation

Bio-inspired structures that achieve high stiffness, strength, and toughness, such as nacre and spider silk, are characterized by unique architectures that integrate rigid and flexible components. This study investigates the mechanical performance of a core-shell dual-material (DM) filaments Fused Filament Fabrication (FFF) printed bio-inspired helicoidal structure under impact loading. Polylactic Acid (PLA) and Thermoplastic Polyurethane (TPU) were selected as the stiff and soft phases, respectively. DM filaments with PLA and TPU as the shell materials were fabricated and printed into specimens for testing. Single-twisted Bouligand-type structure (SBS) and double-twisted Bouligand-type structure (DBS) specimens, made from PLA-shell DM filament, were tested using a drop tower. Tensile tests revealed that the core-shell configuration significantly enhances energy dissipation along the axial direction, while using the stiff material as the shell presents better transverse mechanical performance. Drop tower tests demonstrated that the stiff-shell DM-printed SBS structure delivered the highest impact performance, exhibiting at least 59.8% and 148.5% enhancements in impact performance compared to its conventional printing pattern and the monolithic stiff specimens, respectively. This study highlights the potential of multi-material bio-inspired structures to enhance mechanical performance in both tension and impact loading scenario, offering valuable insights for the design of advanced composite material.