Low-velocity impact behavior of fiber metal laminates

The low-velocity impact response of a range of fiber metal laminate (FML) panels was investigated through testing and finite element simulations. The objective of this study was to understand the impact-damage resistance of these novel composites, so that they can be designed optimally for impact-resistant aircraft applications. The FML panels were made up of aluminum alloy 7475 T761 and unidirectional S2 glass/epoxy oriented in a cross-ply configuration. Experimental tests were performed using a free-fall drop dart testing machine. The plate specimens were constrained on a circular edge by the clamping fixture. The shape and the nature of the damage inflicted by impact were evaluated using both destructive cross-sectional microphotography and nondestructive ultrasonic techniques. The tests showed that FML laminates are capable of absorbing energy through localized plastic deformation and through failure at the interface between the layers. In particular, delaminations occurred in the back face of the aluminum-alloy sheet and its adjacent fiber-reinforced epoxy layer and in between adjacent fiber-reinforced epoxy layer. The finite element code, LS-DYNA3D, was used to perform numerical simulations of low-velocity impact to predict the complex damage propagations. The computed post-impact deformed shapes and damage patterns were found to be fairly close to experimental results.