This paper models the non-linear flexural response of laminates that have piecewise variation of lay-up in the planform, using finite element analysis. Attention is focused on the effects that thermal stresses have on the potential multiple shapes of a composite structure. Unsymmetric laminates may possess more than a single equilibrium configuration, and during the cool-down the solution thus bifurcates at a critical temperature. In static analyses, numerical solutions are often coaxed to converge into one or the other branch of the solution. A methodology to overcome this problem is presented. Such modelling is necessary to allow application of multistable composite within morphing aircraft structures as multistable composites could provide a viable solution for the realisation of shape-adaptable structures.
a b s t r a c tThe non-linear out-of-plane displacements of partially unsymmetric laminates are modelled using both finite element analysis and an analytical method. Attention is focused on the effects that thermal stresses have on the potential multiple shapes of a composite structure. The paper extends previous analytical models which could only take into account ''free-free" boundary conditions. The shape functions that model the out-of-plane displacements are modified to include variations of the curvatures within the domain. The new analytical formulation is compared with literature and finite element analysis for a square plate and then it is tested for laminates with piecewise variation of lay-up in the planform. The results are validated against finite element analysis and experimental tests and a good correlation is obtained. Finally, a parametric study is made on the effect of changing the fibres orientation and the laminate thickness. The results confirm that it is possible to introduce bi-stable composites within structures to obtain systems that are both flexible and stiff depending on the loading environment.
One approach to morphing aircraft is to use bistable or multistable structures that have two or more stable equilibrium configurations to define a discrete set of shapes for the morphing structure. Moving between these stable states may be achieved using an actuation system or by aerodynamic loads. This paper considers three concepts for morphing aircraft based on multistable structures, namely a variable sweep wing, bistable blended winglets and a variable camber trailing edge. The philosophy behind these concepts is outlined, and simulated and experimental results are given.
An experimental investigation into the use of a bistable winglet to enhance the lift characteristics of a wing transitioning from lower to higher subsonic flow speeds is presented in this paper. The concept centers around the use of a specifically designed composite winglet, manufactured with an unsymmetric layup, which, when increasingly loaded, snaps between two stable states. Initially, during low-speed operation, the winglet is fixed in one stable state that is specifically designed to be cambered, thus enhancing the lift capability of the wing. At higher dynamic pressures, the winglet snaps to a configuration more intuitive and conventional to current winglet design. Results presented in this paper show the concept to be viable at enhancing the lift produced by a swept wing as aerodynamic loading increases before snap-through. During snap-through, however, the absence of any method of controlling the snap-through process generated significant dynamic loading that was transmitted, unhindered, throughout the entire test rig.c tip = root and tip chords, m h = winglet height S = wing area, m 2 V = freestream velocity, m s 1 = angle of attack, deg = cant angle, measured as dihedral angle relative to wing plane, deg = sweep angle, deg Subscripts bs = before snap max = maximum min = minimum rms = root mean square tip = tip spanwise location wl = winglet
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