| Due to the objective existence of local conflicts and terrorist attacks, high speed impact dynamics and protective structure design has recently been one of the most active research fields in weapon science. With the increasing mobility and flexibility of tanks, vehicle, warplanes in modern wars, research on new materials and structural designs have already become a heated focus in terms of protective armors. Aluminum alloy material has been widely used in lightweight armor design because of its high strength and low density. Meanwhile, polymer materials have been applied in personal protection techniquesdue to its lower density compared to aluminum and great ductility. In the present dissertation, the impact response and perforation resistance of aluminum/polyethylene bi-layered plates are investigated to provide guidance and instruction for the structural design and application of the doubled-layered composite plates made from 6082-T6 aluminum alloy, low-density polyethylene(LDPE) and ultra-high molecular weight polyethylene(UHMWPE).Combined with material tests and literature review, the parameters of Johnson-cook model to describe the dynamic mechanical behavior of 6082-T6 aluminum can be obtained through fitting; while the C-S models for LDPE and UHMWPE are obtained by quasi-static tensile tests and Split-Hopkinson Bar(SHPB) tests, and verified using finite code Abaqus for further numerical simulations.Rigid projectiles of three different noses(flat, sharp, and semi-spherical) are launched by the ballistic gun system to conduct impact experiments on monolithic and bi-layered plates. The initial-residual velocity curves and ballistic velocities for different configurations of plates can be derived from the experimental data with projectile penetrating plates with different velocities, which are recorded by the high-speed camera system. Later, intensive analysis has been made on the deformation/failure modes of the plates, including shapes of the holes on plates after perforation, the high-speed photography during penetration, and characteristics of plugs.From the ballistic experiments, it indicates that typical deformation/failure mode for monolithic aluminum plates is plugging perforation with regular holes and cylindrical plugs. Under the impact of projectiles with sharp and semi-spherical noses, aluminum plates show radical cracks, which are not shown in cases with flat-nose projectiles. For LDPE and UHMWPE plates with small thicknesses, brittle features can be observed and the typical deformation/failure mode is plugging perforation; while viscoelastic characteristics dominate for the cases with thick plates. Considering penetration resistance within the velocity range of experiments, the composite plates are superior to the monolithic polythene plates with identical areal density, but inferior to the monolithic aluminum plates. Also, a finite element(FE) model is developed based on the typical configuration of composite plates to analyze the energy dissipation. It is found that under projectile impact, the impact energy is mainly dissipated through plastic deformation of aluminum panels, and the polythene panels can also work as a cushion of certain degrees as well. |
