Theoretical-experimental investigation on mechanical response of Al honeycomb sandwich under static compression and high-velocity impact

• Performing quasi-static and ballistic characterization of Al honeycomb sandwich panel • Determining the ballistic limit by a theoretical-experimental integrated approach • Modelling the energy dissipation and mechanical response to perforation • Outlining the roles of honeycomb core in energy absorption and impact load attenuation This paper reports a theoretical-experimental investigation aimed at characterizing the penetration behavior and ballistic limit, the energy absorption capabilities, and the impact force attenuation effect of an Al alloy sandwich panel with honeycomb core 50 mm thick, under normal impact by spherical projectiles. The analytical model used to estimate the ballistic limit has been developed according to the energy conservation-based approach, which allows to evaluate the effect of dissipation mechanisms through the elements constituting the sandwich panel. The experimental investigation has been conducted under quasi-static and high-velocity impact conditions (150-250 m/s), characterizing the out-of-plane compressive behavior and the dynamic response (ballistic limit, absorbed energy, impact force). The theoretical and experimental investigations as a whole outline an integrated approach where analytical modeling, calibrated and validated by experimental results, can be adapted to each specific application, and allows to characterize and predict the potential of the honeycomb core as an effective element for energy dissipation, and impact force attenuation, so to define the actual role for the overall penetration behavior. As main results of the investigation, for the starting configuration of the sandwich a ballistic limit of 195 m/s, an average value of energy absorption of 40.37 J, with about only 15% due to the honeycomb, and an average value of maximum impact load of 0.776 kN has been found, with substantial consistency between experimental and theoretical results. Projections by varying the main geometric parameters of the honeycomb allow to define high-potential conditions for energy absorption increase and further impact force attenuation.