To achieve the synergistic improvement of load-bearing stability and energy absorption in lightweight protective structures, a bio-inspired thin-walled-foam composite structure based on mechanical matching design was proposed. Three configurations of polylactic acid (PLA) bio-inspired shells were fabricated via additive manufacturing, and subsequently filled with polyurethane foam through an in-situ foaming process. Tensile tests, quasi-static compression tests, and drop-weight impact tests were conducted to investigate the foaming-induced thermal effects on the mechanical properties of the PLA shells and the structural response of the composites. Crashworthiness was evaluated using peak crushing force (PCF), plateau force, specific energy absorption (SEA), mean crushing force (MCF), and crushing force efficiency (CFE). Results show that the temperature rise during foaming reduces the elastic modulus and strength of PLA while improving its ductility, thereby enhancing the mechanical compatibility between the shell and foam. Consequently, the composite structures exhibit significantly increased plateau force and MCF, and their collapse mode transforms from local instability to progressive stacked crushing, leading to stable hierarchical energy absorption. Dynamic impact tests further demonstrate the superior load-bearing and energy absorption performance of the composite structures under high-energy impact. The results highlight the synergistic role of geometric configuration, material matching, and thermal-mechanical coupling in regulating the energy absorption behavior, providing guidance for the design of lightweight bio-inspired protective structures.

Fabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramic materials. In nature, mineralized tissues or organisms such as cuttlebones and diatoms have evolved with hierarchical porous structures to overcome this difficulty. A bioinspired design of ceramic lattice structure with pores at multiple length scales, ranging from few nanometers to hundreds of micrometers, is proposed in the present work. These ceramic lattices with hierarchical porous structures were successfully fabricated via 3D cryogenic printing. Under quasi-static compressions, the printed ceramic lattices showed unprecedented long plateau strain (~60%) and a specific energy absorption of ~10 kJ·kg^‒1 with a porosity of ~90%. The resulting energy absorption capability was comparable with most composites and metals, thus overcoming the brittle nature of traditional porous ceramics. This was attributed to the delayed destruction of the lattice structure, as well as the gradual collapse of pores at multiple length scales. Similar trends have also been observed under split Hopkinson pressure bar (SHPB) tests, indicating excellent energy absorption under high strain-rate impacts. The proposed 3D printing technique that produces hierarchical pores was also demonstrated to apply to other functional materials, such as silicon carbide, barium titanate, hydroxyapatite, and even titanium alloy, thus opening up new possibilities for fabricating bioinspired hierarchical porous structures.