Research On Dynamic Response And Damage Characteristics Of Heterogeneous Composite Sandwich Structure Under Projectile Penetration

Composite sandwich structure has been widely applied to various fields,such as aerospace,automotive and shipbuilding,because of its excellent mechanical properties and lightweight characteristics.High-speed penetration,as one of the main dynamic loads facing engineering structures,could cause the structure deformation and damage under the condition of instantaneous high strain rate.How to ensure the reliability of lightweight sandwich structures under such loads is the key for improving the vitality effectively.Based on the above background and combined with the protective characteristics of composite sandwich structure,the study on the dynamic response,damage mechanism and energy absorption characteristics under strong dynamic load is the key for further explaining the protective mechanism of composite sandwich structure and promoting the engineering protection application.Through the experimental,numerical and theoretical analysis methods,the dynamic response,failure and energy absorption protection mechanism of heterogeneous composite sandwich structure under the spherical projectile penetration are studied.The main research contents and results are as follows:(1)Through the light-gas gun loading experiment,the mechanical response of the heterogeneous composite sandwich structure under the forward penetration of the spherical projectile is studied.The dynamic response history of the aluminum alloy/PVC heterogeneous composite sandwich structure after being loaded is clarified by the three-dimensional digital speckle correlation measurement technology(3D-DIC).The results show that the out-of-plane deformation of the sandwich structure under the impacting of projectile is mainly concentrated near the penetrated area,and the deflection value gradually decreases from the center of the rear panel to the periphery,and the distribution is approximately symmetrical.(2)In view of the influence of different penetration angles of the projectile on the response characteristics of the heterogeneous composite sandwich structure,the projectile oblique penetration experimental and simulation studies for the sandwich structure are carried out.Compared with the forward penetration,the deformation of the back panel of the sandwich structure under the oblique penetration gradually evolves from the approximately symmetrical distribution at the initial stage of penetration to the longitudinally asymmetric distribution,and the deformation in the penetrated area decreases with the increase of the penetrated angle.(3)The failure mode and damage mechanism of the heterogeneous composite sandwich structure under the projectile penetration are studied.Based on the experimental and simulation results,the damage map of the sandwich structure of the heterogeneous composite material is established.The results show that the damage modes of the front and rear panels of the sandwich structure show the obvious differences under the forward penetration by projectile.The front and rear panel of the sandwich structure are damaged by shearing and petals,respectively.The front panel under the oblique penetration present the damage of "reverse flaps",and the rear panel breaks away from the center of sandwich panel with the penetration angle increasing.The increase of the density and thickness of the core layer would reduce the final deformation of the sandwich structure but not affect the failure mode of the structure.(4)Considering the factors such as the penetration speed,penetration angle,core layer density,core layer thickness and core layer connected method,the research on the penetration energy absorption characteristics of heterogeneous composite sandwich structures is carried out.The results show that within the speed range in this study,the density and thickness of the core layer could improve the energy absorption efficiency and anti-penetration performance of the sandwich panel at different penetration angle.As the penetration angle increasing,the projectile penetrating path in the core layer of the sandwich structure increases,effectively increasing the dissipation of the projectile kinetic energy for the overall structure.The tendency of energy absorption of composite sandwich structure shows firstly decreasing and then increasing,when the velocity of projectile reaches the ballistic limit velocity of the plate.