Design of a composite morphing wing

Morphing aircraft components can increase the possibility of optimising the performance of an aircraft at various flight conditions. A morphing aircraft wing can change the wing shape to modify the lift and drag distribution on the wing surface, allowing the lift-to-drag ratio to be tailored to the desired performance. A camber morphing and a trailing edge morphing wing changes the aerodynamic lift by altering the camber and by deflecting the wing trailing edge, potentially reducing the aerodynamic drag by eliminating the gaps; which exist between the main wing and the control surfaces of a conventional wing. Among the technology used to achieve camber morphing and trailing edge morphing, were mechanical and smart actuations, such as piezoelectrics and shape memory alloys (SMAs). Compliant structures, cellular structures, shape memory polymers, and multi-stable structures were exploited to improve the flexibility of the aerofoil sections or wings. SMA wires were one of the smart actuators which had been extensively utilised to morph various aerofoils/wings, mainly due to the high actuation force and compatibility, which reduce the volume and weight of the actuators and the complexity of moving mechanical components. In this research, a user defined material model (UMAT) was developed within the explicit LS-DYNA FE code, for NiTi shape memory alloy (SMA) wires, and used for actuation of the composite morphing wing. The Tanaka SMA constitutive model was implemented in MATLAB and FORTRAN codes for the SMA-actuation of various structures. The UMAT was used to simulate actuations of various complex morphing structures, including several aluminium and composite aerofoils with corrugated sections, and a pre-curved corrugated plate. Actuations of the two aluminium aerofoils, with corrugated sections in the lower surface and the middle cantilever section, by a 0.5mm-diameter SMA wire with a maximum recoverable strain or a pre-strain of 1.6%, resulted in trailing edge (TE) deflections of 7.8 mm and 65.9 mm, respectively. Actuation of the carbon fibre (CF) composite aerofoil, with the corrugated section as a middle cantilever section, and with 8 layers of CF in ±45° directions, produced a TE deflection of 52.0 mm. To demonstrate the SMA-actuated morphing concept, a composite 3D-printing technology was explored to manufacture a carbon fibre (CF) composite structure, consisted of a flat vertical front plate, a corrugated section, and a rear trailing edge (TE) section. Due to the nature of 3D-printing, two layers of CF were 3D-printed along the circumference of the corrugation and the TE section, and the minimum thickness of the structure was 3 mm. Experimentally, actuation of the CF composite corrugated structure by a NiTi SMA wire with a diameter of 0.2 mm and a pre-strain of 4.77%, and with a diameter of 0.5 mm and a pre-strain of 1.68%, aligned in the chordwise direction, resulted in 1.1 mm and 6.0 mm TE deflections, respectively. Cyclic tests (10 and 30 cycles) of the actuation of the CF composite corrugated structure showed the TE deflection converged after few cycles. A 1.25m-span composite morphing wing was finally designed and manufactured, consisted of a CF composite D-nose spar which resisted the main aerodynamic loading, and rear sections which were made of rigid and flexible foams. CF composite spar flanges, spar web, front and rear ribs, were 3D-printed, and were assembled with a CF composite skin which was autoclave-manufactured, to form the CF composite D-nose spar. Sections of rigid and flexible foams were CNC-machined and were attached to the front CF composite D-nose spar, 3D-printed long rear ribs, trailing edge sections and the morphed corrugated structure, to form a complete composite morphing wing.Open Acces

Finite-element modelling of NiTi shape-memory wires for morphing aerofoils

This paper presents the development and implementation of a user-defined material (UMAT) model for NiTi Shape-Memory Alloy (SMA) wires for use in LS-DYNA commercial explicit finite-element analysis software. The UMAT focusses on the Shape-Memory Effect (SME), which could be used for actuation of aerostructural components. The actuation of a fundamental structure consisting of an SMA wire connected in series with a linear spring was studied first. The SMA thermomechanical behaviour obtained from the finite-element simulation was compared with that obtained from the analytical solution in MATLAB. A further comparison is presented for an SMA-actuated cantilever beam, showing excellent agreement in terms of the SMA stress and strain as well as the tip deflection of the cantilever beam. A mesh sensitivity study on the SMA wire indicated that one beam element was adequate to accurately predict the SMA thermomechanical behaviour. An analysis of several key parameters showed that, to achieve a high recovery strain, the stiffness of the actuated structure should be minimised while the cross-sectional area of the SMA wire should be maximised. The actuation of an SMA wire under a constant stress/load was also analysed. The SMA material model was finally applied to the design of morphing aluminium and composite aerofoils consisting of corrugated sections, resulting in the prediction of reasonably large trailing-edge deflections (7.8–65.9 mm)

Morphing Wing I - finite element modelling of a NiTi SMA wire

This research aims to model the shape memory effect (SME) of a shape memory alloy (SMA) wire in a commercial explicit finite element analysis (FEA) software, Ls-Dyna. A user defined material (UMAT) model was developed by implementing a one dimensional constitutive model into Ls-Dyna. A simple structure consisting of one SMA wire connected to a linear spring in series was analysed using Ls-Dyna. One complete heating-cooling cycle was applied on the SMA wire, and the resulting stress and strain were validated by analytical solutions. This SMA model was further tested for mesh sensitivity, for a range of values of key parameters, and for fully-constrained and constant load cases. Finally, actuation of several morphing aerofoil sections was studied. Among the proposed aerofoil configurations, an aerofoil with a corrugated plate in between the D-nose spar and the trailing edge (TE) section, with one SMA wire in each cell, provided the highest TE deflection. The results show the applicability of the current model in actuation of the morphing aerofoils