Stretch–bend-hybrid hierarchical composite pyramidal lattice cores

Hierarchical composite pyramidal lattice (CPL) cores with foam-core sandwich struts were designed, and two stacking patterns were fabricated and tested in out-of-plane compression. Analytical expressions for five possible failure modes were derived considering not only stretching and bending deformation but also shear deformation of struts. Core shear failure was absent from collapse mechanism maps for both Patterns-I and II CPL cores. Optimized Pattern-I hierarchical CPL cores were more efficient than Pattern-II cores. The following comparison with almost all competing composite sandwich cores revealed that the hierarchical CPL structures here, the assembly of both stretch- and bend-dominated constructions, could perform among the most efficient sandwich cores. Meanwhile, the construction concept can also enable multifunctionality by judicious selection of strut core materials without compromising structural efficiency.