Additively manufactured high-energy-absorption metamaterials with artificially engineered distribution of bio-inspired hierarchical microstructures

There is an increasing demand of protective lightweight components in aerospace industries, and the high flexibility of additive manufacturing (AM) enables the design of complex structures to achieve such goal. In this study, a novel high-energy-absorption spherical hollow structure (SHS) was first engineered with a layer-wise failure mode and crystal-inspired grain boundaries through the variation of its hierarchical microstructures. To engineer the strength distribution of SHS, the mechanical properties of its spherical unit cells with bendingdominated and stretch-dominated honeycomb microstructures was experimentally studied with respect to different microstructural densities. Simulations were also performed to further reveal their failure mechanisms. Based on the relationship between the microstructural densities and the mechanical responses of these unit cells, a failure mode engineering method was proposed to artificially control the failure sequence of the lattice structure through a microstructural-controlled strength distribution. Here, we demonstrated a laminated failure mode composite hierarchical SHS lattice with crystal-inspired bending and stretch-dominated grains was developed using AM. Compared to different energy-absorption material designs with similar density, the quasistatic compressive results indicated that a hierarchical SHS lattice possesses a 72% improvement in the specific energy absorption, a 50% higher density-normalized plateau stress owing to the constraining effect of its mesoscale grain boundaries, and an increased number of intensively engineered laminated failure levels. This manuscript proposes a new design paradigm of AM high energy-absorption lattice structure for different protective applications.