Experimental and numerical study on the ballistic impact resistance of the CFRP sandwich panel with the X-frame cores

Fiber reinforced composite sandwich structures have wide applications in reducing the weight of high-speed aircrafts due to their processibility and high specific performance. It is of great significance for the safety to study the failure mechanism of composite sandwich structures under the ballistic impact and improve the structural impact resistance. However, the previous researches mainly focus on the performance of the hybrid sandwich structures with foam cores or metal grid cores. The main novelty of this study is to investigate the ballistic impact resistance of a composite composite sandwich panel with the fiber reinforced X-frame cores by using the projectile impact tests and numerical simulations. The impact resistance of this integrally molded fiber reinforced cores is less reported and is expected to be superior than that of the common aluminum, polymer and foam cores. For comparison, the carbon fiber composite cross-ply laminates with the identical areal density and the foam reinforced sandwich panels with the X-frame are tested. The experimental results indicate that the ballistic limit of the X-frame sandwich panel is similar to that of its equivalent laminate under the normal projectile penetration. Filling foams increase the structural ballistic limit velocity and energy absorbing amount by 18.2% and 33.9%, respectively. The widest range of fiber breakage and delamination on the sandwich panel observed appear at impact velocities approaching the ballistic limit, while the local damage is found under the high-speed perforation. The numerical results indicate that the projectile kinetic energy dissipated by the X-frame core accounts for over 50% of the total under the normal impact and the core has the better specific energy absorption capacity than the skins. The impact oblique angle and impact position are found to have a significant effect on the impact resistance of the X-frame sandwich panel through the numerical calculations.