Thin fiber metal laminates comprising functionally graded ballistic-grade fabrics subjected to mechanical and damping characterization

Fiber metal laminates (FMLs) intended for blast and ballistic resistance applications need to contain ballistic grade plies like aramid (Kevlar®), ultra-high molecular weight polyethylene (Spectra®) as supporting plies in addition to the metallic layers. The order of stacking varies depending on the functional grading of plies. In the current work, five sequences of fiber metal laminates made of AA6061-T6, aramid, ultra-high molecular weight polyethylene, and paperboard have been developed. The novelty of the work is the basis of the layering based on functional grading by the shock impedance of the respective plies. The FML sequences were subjected to mechanical characterization comprising flexural and tensile tests, as well as damping characterization for vibration characteristics. The key metrics of areal density, storage modulus, natural frequency, damping coefficient, tensile strength, tensile modulus, tensile strain-to-failure, flexural strength, flexural modulus, flexural strain-to-failure were considered for comparing the different layups of the FMLs. From the experimental studies, placing a low-impedance ply (paperboard layer) as the penultimate layer before the AA6061-T6 rear skin led to the best mechanical and damping performance as seen in the FML sequences BRSP-II and BRSP-IV.