Decomposing Contributions to Energy Dissipation in Impact of Architected Materials

Ultralight mechanical metamaterials enabled by advanced manufacturing processes have previously achieved density-normalized strength and stiffness properties that are inaccessible to bulk materials, but the majority of this work has focused on static loading while the mechanical properties of these metamaterials under dynamic loading conditions have remained largely unexplored. Properties such as energy absorption of these metamaterials are of high interest for protective applications and recent works on their dynamic response have demonstrated the benefit of architecture for impact mitigation.<br/><br/>Here, we systematically study the response of periodic mechanical metamaterials under microprojectile impact using two-photon lithography as a rapid prototyping technique for microscopic polymeric microlattices. We fabricate suspended thin-plate lattice architectures of varying thicknesses and morphologies to characterize their response to microparticle impact. We employ the laser-induced particle impact test method to accelerate ~30 μm-diameter microparticles to velocities of up to 900 m/s, and use ultra high-speed imaging of the impact process to measure impact energetics across multiple architectures and varying lattice plate thicknesses. We compare impact performance to an array of quasistatic uniaxial compression experiments to decompose the effects of lattice compaction and fracture on energy dissipation during impact. Additionally, we analyze our experiments in a dimensionless framework to provide a first-order estimate of impact response across materials and length scales and investigate how the energy dissipation components scale with the regime of impact. Lastly, we study the impact response using an explicit dynamics finite-element representation to provide insight on the impact mechanisms. This investigation provides a framework for the rapid design and characterization of future mechanical metamaterials for a variety of energy absorption applications.