Finite element modeling and design optimization of ceramic and composite structures under ballistic impact

Armors are used to protect aircrafts, vehicles, space crafts, structures, and the human body. The main purpose of the armors is to absorb the kinetic energy of the threat by spreading the impact power to wide areas to reduce the damage. The armors are expected to be lightweight while providing a high level of protection. In addition to their high hardness, ceramic and composite materials are lighter than traditional armor materials. Within the scope of this thesis, ceramic body armors and composite aircraft armors are investigated numerically. The finite element models are developed using LS-DYNA software. Then, the developed models are validated with the literature data. Finally, the validated models are used for design optimization to reduce the weight of the armors without sacrificing from safety. In body armors, ceramic materials are used as a front layer to erode and tear up the threat. Alumina is the most widely used ceramic body armor material. To increase the ballistic protection of the alumina ceramic, there are many options, and one of these options is to create surface profiling on the armor plate. By surface profiling, the penetration power of the threat can be reduced by changing the fly direction. In this thesis, the effect of hemispherical surface profiling on alumina ceramic plates with different diameters is investigated numerically. The effect of surface profiling is investigated through the kinetic energy absorption capacity per unit mass. The alumina plate is modeled by the Johnson Holmquist material model and the Smooth Particle Hydrodynamics (SPH) methods. With the SPH method, the cracks and debris formed by ballistic impact can be modeled without any erosion algorithm. To validate the established finite element model, the flat alumina ceramic plate is modeled and compared with the experimental data obtained from the literature. Then, the ballistic performance of the surface profiled ceramic plate is investigated numerically. With the hemisphere surface profiling, the specific kinetic energy absorption capacity is increased by 56%. Composite materials are preferred especially in the field of aviation. The most widely used composite in the aviation industry is carbon fiber/epoxy composite. The epoxy resin is reinforced with unidirectional carbon fibers so that lightweight but high-strength layers are obtained, and the layers are brought together to form a composite plate. In the design of the composite armor, the thicknesses of plies affect the ballistic performance of the plate. It is therefore important to find the optimum layer thickness with a given ply angle. Carbon fiber/epoxy composite is modeled with the enhanced composite damage material model with a medium-scale modeling method, thin shell elements. To validate the carbon fiber/epoxy composite, low-speed impact analyses are performed and the literature data are verified. Then, the optimum carbon fiber/epoxy armor thickness value is found for the composite armor to withstand the ballistic impact of a threat, which is determined by the standards. By using the support vector machining and genetic algorithm, the optimum thickness values are determined for each ply with different ply angles, and a 6.3% reduction in weight is achived.