Theoretical and experimental investigations on the impact resistance of fiber polymer cylindrical shells with functional gradient protective coatings

A dynamic model of fiber polymer cylindrical shells covered with functional gradient protective coatings (FGCs) is proposed in this work to predict impact characteristics when low-velocity oblique impact loading is considered. The material properties of the FGCs attached to both the inner and outer surfaces of the structures is defined, and the related failure modes and different energy-absorbing mechanisms associated with penetration damage are clarified. Also, by employing the proposed penetration judgement approach based on impact energy, the solution equations are derived to predict the penetrating or non-penetrating dynamic parameters. After constructing the low-speed drop hammer and high-speed gas gun impact systems, detailed tests are conducted to obtain time-history curves of impact forces, force-displacement curves, structural damage areas, and residual impact energies. These results are analyzed for projectiles with different impact velocities and energies. Moreover, these experimental data are compared to the calculated results to fully validate the developed model as well as evaluate the impact resistance of the structure with and without FGCs. Finally, the influence of crucial coating parameters on structural impact resistance is investigated, with several beneficial design suggestions being refined. The dynamic model and solution techniques developed in this work can be readily extended to the impact resistance evaluation of other advanced composite shell structures with coating materials.