Ballistic resistance of spaced multi-layer plate structures: Experiments on Fibre Reinforced Plastic targets and an analytical framework for calculating the ballistic limit

As the use of complex multi-layer structures in defense, marine, aerospace and automotive applications becomes increasingly common, it is vital that the response of such structures to impact loading is better understood and that engineers have adequate analysis tools to design structures optimised for resistance to ballistic penetration. This paper presents the results of a series of ballistic impact experiments carried out on a range of spaced multi-layer fibre reinforced-plastic (FRP) composite targets, with a constant total number of plies per target, but varying numbers of plies per layer and varying layer arrangements. It is shown that varying the ratio of plies between layers can have a significant effect on resistance to ballistic penetration. In light of these experimental results, the validity of applying the Lambert–Jonas equation to spaced multi-layer structures is discussed and an extended framework developed to determine the ballistic limit of a projectile impacting such a structure. The extended Lambert–Jonas framework is then validated with data from the literature. It is hoped that this framework will allow engineers to quickly determine the optimum layer arrangement to maximise the ballistic resistance of complex spaced multi-layer structures.