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Fibre metal laminates were developed at Delft University during the last two decades as a family of new hybrid materials consisting of bonded thin metal sheets and fibre/adhesive layers. This laminated structure provides the material with excellent fatigue, impact and damage tolerance characteristics and a low density. While the 20 per cent weight reduction was the prime driver behind the development of this new family of materials, it turns out that additional benefits like cost reduction and an improved safety level have become more and more important. The combination of these aspects in one material makes fibre metal laminates a strong candidate material for fuselage skin structures of the new generation of high capacity aircraft. The focus on this application currently leads to industrialization and qualification that makes this material available to the aircraft designer.

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Fatigue crack propagation tests were carried out in different environments on 7075-T6 and 2024-T3 centre-cracked sheet specimens. Observations were made on the macroscopic transition from tensile mode to shear mode. The transition is suppressed by an aggressive environment, whereas it is promoted by an inert environment. As a consequence there is no unique correlation between the state of stress and the mode of cracking. Both the state of stress and the environment have a significant effect on the mode of cracking. A simple model for the effect of environment on fatigue crack growth is presented. The implications for crack growth under corrosion fatigue conditions are discussed. a daldn AK R t 0 7 0 c r

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A new material for aircraft structures with several promising properties is described. The material is obtained by the adhesive bonding of a number of thin aluminum alloy sheets and aramid layers to produce an aramid reinforced aluminum laminate (ARALL). ARALL shows very favorable fatigue crack growth properties and has a high tensile yield strength. This is especially true if suitable residual stresses are introduced into a laminate with an optimum thickness of metal sheets. In spite of the use of structural fibers in the laminates, nearly all advantages of metals over pure composites are preserved such as plasticity, impact strength, formability, and easy machining.

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