Influence of metal layer distribution on the projectiles impact response of glass fiber reinforced aluminum laminates

The effect of the distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their projectiles impact response is studied using high speed 3D digital image correlation technique (DIC). The FMLs consisting of aluminum alloy 2024-T3 sheets of thicknesses 0.3 mm, 0.4 mm, and 0.6 mm and glass fiber reinforced epoxy layers (two layers with each of 0° and 90°) were prepared by the hand layup process followed by vacuum bagging. The metallic layers are placed at different locations through the thickness of four different layups while keeping the total metal layer thickness constant. The hemispherical and conical nose projectiles of the same mass are impacted normal to the FMLs plate using nitrogen gas gun. The performance of the FMLs is evaluated using different parameters such as the deformation history, residual deformation and also the surface and internal damages. FML 4/3-0.3 in which the two adjacent composite layers with different fiber orientations separating by an aluminum layer exhibited the highest deformation with hemispherical projectile impact for the same impact energy level. The deformation was found to be lower and nearly same for the other three FMLs. This observation is also noticed in the case of drop weight impact (low velocity impact). The FML 2/1-0.6 in which the composite layers were stacked together exhibited a comparatively higher lateral spread of delamination and interlayer opening with hemispherical projectile impact when compared to FML 4/3-0.3, indicating that the lateral spread of damage within the FML can be decreased by distributing the aluminum layers in the FML. This is also observed in the case of drop weight impact.