DAMOCLES 2 – STRUCTURAL ANALYSIS AND OPTIMISATION OF AN ‘ALL COMPOSITE’ DAMAGE TOLERANT WINGBOX

Carbon fibre reinforced plastics (CFRP) are widely used in aerospace structures because they offer excellent properties, such as resistance against fatigue and corrosion, with significant weight savings. However, when in service, they are subject to impact threats such as dropped tools, runway debris or hail and the induced damage which may not be visible, can lead to significant strength reductions. Currently, individual methods for design, inspection, damage assessment and repair of composite structures are available, used albeit at various levels of confidence. Since a cost-effective, through life, service performance is a primary requirement, a need exists for a comprehensive methodology to allow the damage management of composite aircraft structures, based on an integrated approach towards design, inspection, assessment and repair. This paper describes this process with respect to a representative CFRP wingbox structure. This programme of work has been conducted under the WEAG THALES Joint European Programme JP 3.29 DAmage Management Of Composite Structures for Cost Effective Life Extensive Service (DAMOCLES) collaborative agreement between the UK, Italy and the Netherlands. The results presented consider alternative manufacturing methods and through-thickness enhancement (stitching and Z-pins) to optimise a monolithic stiffened structure in terms of weight, performance and damage tolerance. The paper is divided into three sections and summarises the design optimisation; linear and non-linear buckling analysis of the structure and impact event: and the manufacture and structural verification. Conclusions to date are presented, that show the limitations and structural advantages of through-thickness reinforcement in suppressing delamination growth.