Alternative Manufacturing Route of Fibre Metal Laminates

Abstract

Fibre metal laminates (FML) are manufactured by stacking metal sheets and fibre reinforced prepreg in an alternating fashion, and curing it in an autoclave. The most well-known FML is Glare, which has been successfully applied on Airbus A380 for its fuselage skin. It consists of aluminium sheets and glass fibre prepregs. FMLs have a better impact and fatigue performance compared to the bare metal and are therefore more damage tolerant. The drawback of Glare is the high manufacturing cost because of the use of an autoclave and the expensive prepregs. This study investigates the feasibility of vacuum infusion for the manufacturing of FMLs to reduce costs, while keeping an acceptable fibre volume content of 45% to 60%. An experimental approach is taken to explore the manufacturing process to determine under which conditions an infusion is possible, and to analyse which process parameters influence the duration of the infusion. Three variables: resin viscosity, vacuum infusion pressure and the reinforcement permeability are identified from Darcy’s law, which can influence the infusion process. The experimental data was gathered through multiple infusion process tests by adjusting these variables. Because the resin flow on the composite layers cannot be monitored visually through the metal sheets, glass plates are used to investigate these variables’ effect on the process. Through the analysis of the experimental data, the vacuum infusion process including the material selection, equipment and processing details are determined. Aluminium and dry glass fibre sheets are used to conduct the Vacuum Infusion process. The product is used to verify how the process parameters adhere to actual FML product fabrication. It can be concluded that during the experimental study, the Vacuum Infusion process has successfully been applied on the manufacturing of Fibre Metal Laminates with a satisfying fibre volume content of 54% to 65%, and a void content of 0.5% to 1.5%. By extrapolating the experimental infusion length curves, it was estimated that under the current conditions a maximum infusion length of 1.4 m most likely is possible when infused over the 0º direction, and a maximum infusion length of 1.0 m is expected to be possible when infused over the $90\degree$ direction. The total manufacturing cost of Vacuum Infusion process was found to be reduced 43% compared to the autoclave manufacturing process. These results show that vacuum infusion is a promising technique for the manufacturing of low cost FML, and it opens a door for future research on this topic to reduce the manufacturing cost of Glare.