Response of hybrid plate-rod lattices to static and dynamic compression–An experimental study

In general, lattices are frequently composed of cells that are defined by struts or plates (shells), and each has its unique advantages and limitations in terms of load-bearing and energy dissipation under gross deformation. The hybrid plate-rod lattice structure in this study combines favorable features of these two basic constituent topologies, to achieve superior energy absorption properties under impact. The hybrid structure is established by combining a semi-open Octet-Plate lattice (SOPL) and a strut or rod-based open-cell lattice, to form a hybrid plate-rod lattice (HPRL), amenable to fabrication via selective laser melting (SLM). To elicit the quasi-static and dynamic mechanical response of the structures investigated, planar compression was applied to both SOPL and HPRL specimens using a universal testing machine, a high-speed compression tester, and a direct-impact Hopkinson pressure bar (DHPB); these generated quasi-static, medium strain rate, and high strain rate deformation respectively. Applicability of the DHPB and single wave data processing technique in obtaining valid experimental results was verified by digital image correlation (DIC). The test results show that the HPRL exhibits superior mechanical behavior and energy absorption compared to its SOPL counterpart, for both quasi-static and impact compression. Significant rate sensitivity of the responses was also observed. For impact at 57 m/s, the plateau stress and energy absorption of the HPRL both increase by approximately 30 %, above their respective values for quasi-static deformation. By using two specimen mounting approaches in DHPB tests, this study also demonstrates fulfillment of specimen stress equilibrium, inertia effects, and strain-rate sensitivity of HPRL lattices during high-speed compression. For impact velocities below 57 m/s, inertia effects are not obvious, and the elevation in stress can be attributed primarily to material strain rate sensitivity; beyond 57 m/s, inertia effects and stress non-uniformity begin to be manifested. In essence, this effort highlights the advantages of combining cells of dissimilar geometrical characteristics to attain enhanced responses, and the potential of applying this approach to other cell configurations.