Scaling effects in the tensile behavior of fiber-metal laminates

A study of scaling effects in a new lightweight fiber-metal laminate (FML) system has been undertaken. The FMLs were based on an aluminum alloy, a self-reinforced polypropylene composite and a polypropylene film acting as an interlayer adhesive. The investigation focuses on the feasibility of using scale models to predict the full-scale behavior of laminates based on [Aln, 0°/90°n]s and [Aln, ±45°n]s stacking configurations. Tensile tests were undertaken on laminates that were prepared using three different scaling approaches, these being 1D (scaling the thickness dimension), 2D (scaling the in-plane dimensions) and 3D scaling where all of the dimensions were scaled appropriately. Geometrical effects were investigated by monitoring the stiffness, strength, strain to failure and the stress/strain response of the FMLs. In the 1D and 3D-scaled samples, a small decrease in tensile strength was observed with increasing scale size, an effect that was associated with a change in failure mode from tensile fracture to interply delamination. In contrast, the strength of the 2D-scaled samples increased with increasing scale size, an effect that was attributed to the decreasing influence of edge delaminations in the larger test samples. The elastic modulus of the fiber-metal laminates did not exhibit any scale effect, remaining roughly constant over the four sizes of specimen considered here.