Compressive efficiency of stretch–stretch-hybrid hierarchical composite lattice cores

• Novel stretch-stretch-hybrid hierarchical cores are produced, analyzed and tested.
• Efficiency of hierarchical structures was affected by the ratio of lengths at two scales.
• The optimized hierarchical cores were 5 times stronger than conventional lattice cores.
• Effects of macroscopic and mesoscopic topologies were discussed.

Composite lattice cores featuring structural hierarchy were developed to achieve greater buckling resistance. The stretch–stretch-hybrid hierarchical lattice cores were fabricated with a two-step approach by assembling composite pyramidal lattice (CPL) sandwiches into macroscopic truss configurations. Analysis and experiments were performed to determine the out-of-plane compressive strength. Hierarchical CPL cores were evaluated based on their failure mechanism maps, and the structural efficiency was affected by the ratio of strut length at different scales (e.g. L/l1). With the specific limited L/l1, the optimized hierarchical CPL core was almost 5 times stronger than lower-order CPL cores with rectangular trusses (at relative density 0.01). The fully optimized hierarchical CPL cores can be as efficient as optimized CPL cores with hollow trusses. Effects of topologies at two different length scales on the performance of hierarchical structures were also assessed.