The impact resistance of polypropylene-based fibre-metal laminates

The high velocity impact response of a range of polypropylene-based fibre-metal laminate (FML) structures has been investigated. Initial tests were conducted on simple FML sandwich structures based on 2024-O and 2024-T3 aluminium alloy skins and a polypropylene fibre reinforced polypropylene (PP/PP) composite core. Here, it was shown that laminates based on the stronger 2024-T3 alloy offered a superior perforation resistance to those based on the 2024-O system. Tests were also conducted on multi-layered materials in which the composite plies were dispersed between more than two aluminium sheets. For a given target thickness, the multi-layered laminates offered a superior perforation resistance to the sandwich laminates. The perforation resistances of the various laminates investigated here were compared by determining the specific perforation energy (s.p.e.) of each system. Here, the sandwich FMLs based on the low density PP/PP core out-performed the multi-layer systems, offering s.p.e.'s roughly double that exhibited by a similar Kevlar-based laminate. A closer examination of the panels highlighted a number of failure mechanisms such as ductile tearing, delamination and fibre failure in the composite plies as well as permanent plastic deformation, thinning and shear fracture in the metal layers. Finally, the perforation threshold of all of the FML structures was predicted using the Reid-Wen perforation model. Here, it was found that the predictions offered by this simple model were in good agreement with the experimental data.