A unified approach to predicting failure in composite structures with geometrical discontinuities

Advanced composite materials continue to find increased use in the development of new lightweight aerostructures. This technology will play a major role in realising the European Union's 2020 vision of Aeronautics which aims to reduce fuel consumption by 50% and Nitrous Oxide emissions by 80%. Numerous challenges need to be overcome before a structural design capability is developed to meet these targets. Central to this is the joining of composite components. These are not well suited to mechanical fastening and bonding is the preferred option. This bonding may be achieved through co-curing, where the components making up a section are positioned in place and cured in one operation; co-bonding, where one part is cured and other parts are positioned in their pre-cured state and then the whole assembly is cured, or secondary bonding where the individual components are cured separately and then bonded together using an adhesive. These bonding schemes need to be used with caution, particularly in the presence of geometric discontinuities where high interlaminar stresses are only resisted by the relatively weak through-thickness strength of the adhesive or resin. Damage initiation and progression in these vulnerable regions is still difficult to predict and this has lead to conservative composite designs in aerostructures including a 'no-buckling' criterion up to ultimate design load in some instances. To date, no effective unified capability exists in the UK (and possibly elsewhere) to capture the various possible failure mechanisms which may occur within a realistic aerospace composite structure. Particularly important are the large variety of geometrical discontinuities which may induce significant through-thickness stresses. The aim of this proposal is to develop a robust and user-friendly modelling tool to allow the prediction of damage initiation followed by propagation, which may be unstable to failure or arrested at a structural feature.This will reduce the extent of component testing currently necessary to verify structural integrity, as well as providing a powerful tool to be used for the creation of non-conventional airframes with superior performance.