The aim of the paper is to experimentally validate a numerical design methodology for optimizing composite wings subject to gust and fatigue loading requirements and to assess the effect of fatigue on the aeroelastic performance of the wing. Traditionally, to account for fatigue in composite design, a knockdown factor on the maximum stress allowable is applied, resulting in a conservative design. In the current design methodology, an analytical fatigue model is used to reduce the conservativeness and exploit the potential of composite materials. To validate the proposed analytical model, a rectangular composite wing is designed and manufactured to be critical in strength, buckling and fatigue. An experimental campaign comprising wind tunnel and fatigue tests is performed. In the wind tunnel, both static and dynamic aeroelastic experiments are conducted to validate the numerical dynamic aeroelastic model. The fatigue test is used to validate the analytical fatigue model and to understand the effect of fatigue on aeroelastic properties of the wings. The results from experimental campaign validated both the aeroelastic predictions as well as fatigue predictions of the numerical design methodology. However the fatigue process resulted in degradation of the wing stiffness leading to change in the aeroelastic response of the wing. 

More then 10 years ago a large investment was made in extending the NSMB Navier Stokes Multi Block (NSMB) Computational Fluid Dynamics (CFD) towards Fluid Structure Interaction (FSI) simulations (Guillaume et al. in Fluid structure interaction simulation on the F/A-18 vertical tail, 2010 [1], Guillaume et al. in Aeronaut J 115:285–294, 2011 [2]). At that time a segregated approach was adopted using a loosely coupled approach. More recently NSMB was coupled to the open-source Finite Element Analysis environment B2000++ (http://www.smr.ch/products/b2000/ [3]) in a strongly coupled approach. This has led to the possibility to perform both static and dynamic FSI simulations using either a modal or a FEM approach without the need to interrupt the simulation. Results of aero-elastic simulations for the MDO-aircraft, the AGARD445.6 wing and for a Strut Braced Wing configuration will be presented.

An analytical model to predict the fatigue life of a composite laminate is formulated. The model calculates stresses in each ply using classical lamination theory, degrades the residual strength using the linear wear-out law and predicts failure based on Tsai Wu failure theory. The cycles to failure are predicted using the updated cycle-by-cycle probability of failure. The predictions are validated for both a constant amplitude and a variable amplitude loading on a Glass/Epoxy laminate. Additionally the analytical model is extended to work with laminates described using lamination parameters instead of ply angles and stacking sequence. The analytical fatigue model is then integrated in the TU Delft aeroelastic and structural optimization tool PROTEUS. A thickness and stiffness optimization of the NASA Common Research Model (CRM) wing has been carried out. Results show that fatigue, strength and stiffness are the design drivers in the aeroelastic optimization of a composite wing. Furthermore, by including the analytical fatigue model instead of using a traditional knockdown factor to account for fatigue, a lighter wing is obtained.

The research and innovation AGILE project developed the next generation of aircraft Multidisciplinary Design and Optimization processes, which target significant reductions in aircraft development costs and time to market, leading to more cost-effective and greener aircraft solutions. The high level objective is the reduction of the lead time of 40% with respect to the current state-of-the-art. 19 industry, research and academia partners from Europe, Canada and Russia developed solutions to cope with the challenges of collaborative design and optimization of complex products. In order to accelerate the deployment of large-scale, collaborative multidisciplinary design and optimization (MDO), a novel methodology, the so-called AGILE Paradigm, has been developed. Furthermore, the AGILE project has developed and released a set of open technologies enabling the implementation of the AGILE Paradigm approach. The collection of all the technologies constitutes AGILE Framework, which has been deployed for the design and the optimization of multiple aircraft configurations. This paper focuses on the application of the AGILE Paradigm on seven novel aircraft configurations, proving the achievement of the project’s objectives.

The paper describes the deployment of the AGILE Development Framework to investigate the Strut Braced Wing aircraft configuration. The design process consists of a multilevel multidisciplinary architecture, progressing from the initial conceptual synthesis to the physics based analysis. All the main disciplinary domains, including on board system design and cost assessment, are accounted for in the assembled workflow. Due to the specific characteristics of the Strut Braced Wing configuration, the aeroelastic analysis is the main focus of the study and it is addressed at both high and low fidelity levels. The integration of the engine-wing system is also included in the design process. All the design competences, which are hosted at the different partners, communicate via CPACS (Common Parametric Aircraft Configuration Schema) data schema. All the results generated, including the multidisciplinary design process itself, will be published and made available as part of the AGILE Overall Aircraft Design database.

An analytical model to predict the fatigue life of a composite laminate is discussed. It is based on the method developed by Kassapoglou to predict fatigue failure. The analytical model calculates stresses in each ply using classical lamination theory, degrades the residual strength using the linear degradation law and predicts failure based on Tsai Wu failure theory. The cycles to failure are predicted using the updated cycle-by-cycle probability of failure. The predictions are validated for both a constant amplitude and a variable amplitude loading on a Glass/Epoxy laminate. Furthermore the analytical model is extended to work with laminates described using lamination parameters instead of ply angles and stacking sequence. The analytical fatigue model is then integrated in the TU Delft aeroelastic and structural optimization tool PROTEUS. A thickness and stiffness optimization of the NASA Common Research Model (CRM) wing has been carried out. Results show that fatigue may play an important role in the aeroelastic optimization of a composite wing.