Melikasadat Alavi - Mechanical Engineering Department, Amirkabir University of Technology, Tehran
Mojtaba Sadighi - Mechanical Engineering Department, Amirkabir University of Technology, Tehran
Reza Hedayati - Department of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran

This paper explores the impact responses of sandwich structures employing diverse core designs, including pure honeycomb, pure auxetic, and gradient structures including negative-to-positive (NTP), positive-to-negative (PTN), negative-to-positive-to-negative (NTPTN), and positive-to-negative-to-positive (PTNTP). The investigation utilizes the LS-DYNA code to simulate impact loading inducing bending in sandwich panels. Notably, in the gradient NTP and gradient PTN cases, the core layers' Poisson's ratio varies from negative to positive and positive to negative, respectively. This variation is similarly applied to symmetric gradient structures (gradient NTPTN and gradient PTNTP). The results of numerical models exposed to impactors with initial velocities of ۱۰ and ۳۰ m/s reveal that structures with negative Poisson's ratio at their top surface exhibit minimal penetration in both impact velocities. Remarkably, symmetric gradient structures (gradient PTNTP and gradient NTPTN) demonstrate superior energy absorption capabilities, indicating their potential in impact-resistant applications. The study concludes that structures such as gradient NTPTN and gradient NTP excel in situations requiring simultaneous maximum energy absorption and minimal damage to the sandwich structure, providing valuable insights into the design and application of these innovative materials.

Sandwich panels, Gradient cores, Impact loading, Bending-induced behavior, Energy absorption