USE OF EXPANDABLE MULTI-LAYER METAL LAMINATES AS FIRE PROTECTECTION FOR ALUMINIUM AND CFRP AEROSPACES STRUCTURES

Their relatively poor fire performance under load is a significant drawback for both aluminium and composite structures. Exposed to significant heat flux, aluminium in tension or compression fails by a combination of yield and creep. Carbon composite structures behave well in tension but poorly in compression, where their behaviour is limited by the resin reaching its glass transition temperature. None of the accepted means of fire protection is viable in case of external surfaces of aerospace structures. Passive fire protective coatings, including intumescents, would be unsightly and unlikely to survive flight conditions. Furthermore, these coatings are parasitic as they contribute to the weight of the structure without improving its strength. One attractive solution is the use of multi-layer metal laminates, bonded to the exterior of the structure. Such laminates are weight-effective and do not detract from appearance. Exposed to high temperatures these laminates will debond, producing a multi-layer expanded structure of low thermal conductivity which limits the heat flux passing into the substrate. This paper reports a study of the use of 10- and 20-layer thick aluminium/epoxy laminates to protect aluminium plates and carbon/epoxy laminates. The protection layers were 30 micron thick foils, separated by 10micron layers of epoxy resin. Both the aluminium and the CFRP substrates were 6.35mm thick. 100mm by 50mm regions of the protected surface were subjected to a 50kW/m(2) radiant heat flux. The substrates were clamped in the grips of a testing machine and loaded at a defined fraction of the room temperature failure load. The effect of the fire protection was to significantly reduce the temperature reached in the aluminium and CFRP specimens. Stress-rupture relationships in fire are reported for both sample types in the form of curves of failure time vs. stress. These show considerable improvements in the fire durability of the systems examined.