The fracture properties of a fibre–metal laminate based on magnesium alloy

Abstract

A range of fibre–metal laminates (FML) based on a lightweight magnesium alloy have been manufactured and tested. Two types of composite reinforcement have been investigated, a woven carbon fibre reinforced epoxy and a unidirectional glass fibre reinforced polypropylene. Initial tests using the single cantilever beam geometry (SCB) have shown that little or no surface treatment is required to achieve a relatively strong bond between the composite plies and the magnesium alloy. Tests on both types of laminate indicated that increasing the volume fraction of composite, V c, in the FML resulted in a significant increase in its tensile strength. Similar tests showed that the addition of the woven carbon fibre/epoxy plies did not have any effect on the Young's modulus of the FML whereas increasing the V c of the glass/polypropylene plies resulted in a continuous decrease in the modulus of these thermoplastic–matrix systems. Fatigue tests on both types of laminate highlighted the positive contribution of the composite plies in the FMLs. Here, the crack growth rates in centre-notched tension specimens were significantly lower in the FMLs than in the plain magnesium alloy system. Low velocity impact tests on the FMLs highlighted their excellent energy-absorbing characteristics relative to two aluminium-based FMLs. The specific perforation energy of the glass fibre/PP laminate was higher than that offered by a similar aluminium alloy FML and significantly higher than that for a glass reinforced epoxy/aluminium FML. Here, extensive delamination and shear fracture in the outer magnesium alloy plies were found to contribute to the energy-absorbing capacity of these laminates.