Deformation stabilization of lattice structures via foam addition

Stochastic foams are soft but absorb energy efficiently under compressive loading; in contrast, periodic lattice structures are strong but generally exhibit poor energy-absorbing characteristics. Here we present and assess a hierarchical composite concept that aims to combine the desirable attributes of stochastic foams and lattice structures. The composite comprises a low-density polymer lattice structure with centimeter-scale voids and stochastic foam with pores in the sub-millimeter scale in the spaces between the lattice struts. The assessment is made on the basis of compressive response. We show that the post-yielding strength of the lattice can be doubled with the addition of even a weak (low-density) foam: the strength exceeds the combined contributions from the lattice structure and the foam alone. Addition of slightly denser foams can lead to an even larger strength increase. Using X-ray computed tomography, we show that the strength elevation is attributable to the stabilization of the strut members against buckling when surrounded by foam. Finite-element calculations of lattice structures alone and lattice/foam composites show similar characteristics. This composite concept may allow attainment of combinations of strength and energy absorption capacity that cannot be accessed by either foams or lattice structures alone.