Mechanical response and energy absorption of architected granular media

• Introduce architected granular media (AGMs) as new energy absorbing composites. • AGMs can increase energy absorption by approximately 700% over the empty lattice. • AGM mechanical response depends on lattice geometry and granular media parameters. • Propose a mechanical interpretation of constituent interactions during AGM compression. • Hybrid AGMs can be designed to exhibit unnatural deformation modes and fracture. Both architected materials and granular media have been independently shown to significantly improve mechanical energy absorption by intentionally leveraging different energy dissipation mechanisms. Yet it is almost completely unknown how these two classes of materials can be combined to beneficially interact under compression to failure. Herein, we propose the concept of “architected granular media”, or AGMs, where an architected lattice is filled with granular media and show their combination can increase specific energy absorption up to 80% over the empty lattice. We experimentally characterize the quasi-static stress-strain compressional response to failure of auxetic and non-auxetic AGMs filled with different types of granular media, supported by image analysis, flowability measurements, and micro-CT. Results show that the auxetic AGMs preferentially activate the embedded granular media to increase specific energy absorption, and the embedded granular media properties dictate failure modes and stress-strain response. Finally, we show that patterned AGMs, where different granular media are filled in different portions of the lattice, can control failure in a predictable way, opening the possibility of engineered failure with AGMs. This paper demonstrates AGMs are promising for certain energy absorbing applications and could improve critical protective devices such as wave shielding, mechanical impact and crashworthiness, aerospace materials, and sports gear.