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Abstract  This paper investigates the design optimisation of a fuel flow vent hole (FFVH) located in the wing pivot fitting (WPF) of an F-111 aircraft assuming a damage tolerance design philosophy. The design of the vent hole shape is undertaken considering the basic durability based design objectives of stress, residual (fracture) strength, and fatigue life. Initially, a stress based optimised shape is determined. Damage tolerance based design optimisation is then undertaken to determine the shape of the cutout so as to maximise its residual strength and fatigue life. For stress optimisation, the problem is analysed using the gradient-less biological algorithm and the gradient-based nonlinear programming methods. The optimum designs predicted by the two fundamentally different optimisation algorithms agree well. The optimum shapes of the vent hole are subsequently determined considering residual strength and fatigue life as the distinct design objectives in the presence of numerous 3D cracks located along the vent hole boundary. A number of crack cases are considered to investigate how the crack size affects the optimal shapes. A semi-analytical method is employed for computation of the stress intensity factors (SIF), and an analytical crack closure model is subsequently used to evaluate the fatigue life. The 3D biological algorithm is used for designing the cutout profiles that optimise residual strength and fatigue life of the component. An improved residual strength/fatigue life (depending on the optimisation objective) is achieved for the optimal designs. The variability in SIF/fatigue life around the cutout boundary is reduced, thereby making the shape more evenly fracture/fatigue critical. The vent hole shapes optimised for stress, residual strength, and fatigue life are different from each other for a given nature and size of the flaws. This emphasises the need to consider residual strength and/or fatigue life as the explicit design objective. The durability based optimal vent hole shapes depend on the initial and final crack sizes. It is also shown that a damage tolerance optimisation additionally produces a reduced weight WPF component, which is highly desirable for aerospace industries. The design space near the ‘optimal’ region is found to be flat. This allows us to achieve a considerable enhancement in fatigue performance without precisely identifying the local/global optimum solution, and also enables us to select a reduced weight ‘near optimal’ design rather than the precise optimal shape. [ABSTRACT FROM AUTHOR]

Unlike a conventional aircraft’s wing, a morphing aircraft’s wing could undergo large deformations in order to fly efficiently. This requires a wing’s skin meeting conflicting requirements such as large deformation capability to allow morphing of the underlying structure and high flexural stiffness to maintain the airfoil shape. In this paper, the design of composite skins with a cellular core is considered for the particular case of one-dimensional morphing. Cellular core topologies are calculated using a multi-objective genetic algorithm coupled with a local search optimizer. Morphological filtering is used to remove small features in the topology. As a multi-objective problem, no single solution emerges as the clear best solution because of conflicting objectives. However, the solutions found help guide the design of cellular-based morphing skins. A design is selected from the set of solutions obtained, and a cellular core under combined in-plane morphing and out-of-plane loading is examined with respect to the local stresses, the energy of deformation and the core’s out-of-plane deformation to validate the approach used. [ABSTRACT FROM AUTHOR]