Glare Design Aspects and Philosophies

The very nature of Glare is its crack bridging mechanism, which provides superior damage tolerance properties. Depending on the property, Glare shows either monolithic metal or composite behaviour, which challenges the definition of strength justification and certification procedures. Airworthiness regulations have to be interpreted for Glare in order to guarantee the same level of safety as obtained for aircraft structures made of other materials and to take at the same time benefit of its particular properties. Cut-outs are highly fatigue sensitive due to the stress concentrations they cause. In aircraft fuselages these cut-outs are quite large in the case of the windows and doors. The stress level may be increased through the application of Glare in the doubler packages, due to the improved fatigue behaviour compared to conventional aluminium. Glare also presents the possibility of tailoring the material to the load, i.e. fibres aligned with the load, e.g., a 45 degree orientation. FE analysis defined the total doubler package and a test programme was run to confirm the behaviour of the material and to predict the crack behaviour of the Glare door corner. Some aspects of the detailed design of aircraft structures in Glare, the design of splices and riveted joints are discussed. In order to apply Glare in very large fuselage panels, a splice concept was developed, which allows a number of longitudinal splices to be cured in the same curing cycle as the basic material. Through the introduction of this splicing concept, the width of a panel is no longer limited to the maximum width of the aluminium sheet. Internal local reinforcements (doublers) can be integrated into the panel during lay-up. A discussion on the design of riveted joints in Glare is held.