Numerical Modelling and Interaction of Crack and Aeroelastic Behaviour of Composite Structure for Aerospace Applications

Aeroelasticity and fracture mechanics are two fields that commonly known will result in a structural failure. However, small attention is given in assessing the structural integrity of any flying object in aerospace application subjected to aerodynamic or aeroelastic loads especially the aircraft wing. The current research in the aircraft industry is focusing on the development of advanced composite wing structure, which there are still not well explored widely. Due to the higher strength of composite materials, a stronger wing could be designed to sustain the aerodynamic loads or any gust turbulence during flying at high altitude. This situation will be severely dangerous in the event of having a crack or damage on the surface of the cruising wing structure. This research aims at investigating the structural integrity of composite plate, either undamaged or with damage (with crack) subjected to the aerodynamic loads. The purpose of this study is to provide a novel numerical modelling in predicting the application of aerodynamic loads, by observing the flight maneuver safety margin including the flutter speed determination. Initially, the flutter speed was computed based on the coupled of finite element method (FEM) for the structural modelling and the doublet lattice method (DLM) in MSC Nastran for the unsteady aerodynamic modelling. Both structural and aerodynamic models were connected by interpolation using spline. In the end, the safety flight envelope for the composite plate was plotted based on the regulations provided by the Federal Aviation Regulations (FAR) 23. The numerical predictions of crack propagations of the damaged composite structure were determined by implementing the extended finite element model (XFEM), subjected to the aerodynamic loads intercorrelated through Fourier Series Function (FSF). Significantly, the aerodynamic loads were predicted by the implementation of gust, which produced the same level of maximum deflection analysed via aero-static analysis. The results show that the fibre orientation of the composite plate contributes significant crack propagations under the cruising aerodynamic loads. The same procedures were repeated to the wing box prototype developed under the joint program of Indonesian Aerospace, National Institute of Aeronautics and Space of Indonesia and Agency for Assessment and Application of Technology of Indonesia. For this work, the wing fracture was investigated
by the influence of turbulence, called discrete 'gust loads'. From here, FSF was used to combine the wingtip deflection under the gust load influence, and hence applied XFEM to model the crack propagations. The results show that the crack propagated at the lower-front skin near to the wing root.