Shape memory alloys (SMAs) are a unique class of metallic materials with the ability to recover their original shape at certain characteristic temperatures (shape memory effect), even under high applied loads and large inelastic deformations, or to undergo large strains without plastic deformation or failure (super-elasticity). In this review, we describe the main features of SMAs, their constitutive models and their properties. We also review the fatigue behavior of SMAs and some methods adopted to remove or reduce its undesirable effects. SMAs have been used in a wide variety of applications in different fields. In this review, we focus on the use of shape memory alloys in the context of morphing aircraft, with particular emphasis on variable twist and camber, and also on actuation bandwidth and reduction of power consumption. These applications prove particularly challenging because novel configurations are adopted to maximize integration and effectiveness of SMAs, which play the role of an actuator (using the shape memory effect), often combined with structural, load-carrying capabilities. Iterative and multi-disciplinary modeling is therefore necessary due to the fluid-structure interaction combined with the nonlinear behavior of SMAs.
A coupled, partitioned fluid-structure interaction analysis is introduced for calculation of the deformed equilibrium shape, aerodynamic coefficients, and actuation requirements of the Fish Bone Active Camber morphing concept. The Fish Bone Active Camber concept is a high authority morphing camber architecture with a broad range of applications; including fixed wing aircraft, helicopters, wind turbines, and tidal stream turbines. The low chordwise bending stiffness of the morphing structure, high stiffness of the tendon drive system, and the large changes in aerodynamic loading while morphing necessitate a coupled fluid-structure interaction analysis for determination of the static equilibrium. An Euler-Bernoulli beam theory based analytical model of the structure is introduced and validated. Aerodynamic loads are found using XFOIL software, which couples a potential flow panel method with a viscous boundary layer solver. Finally, the tendons are modeled as linear stiffness elements whose internal strains are found from Euler-Bernoulli theory and whose axial forces create bending moments on the spine at their discrete mounting points. Convergence of the FSI code is stabilized through incorporation of relaxation parameters. Results for two chosen test cases are presented to give insight into the mechanical and aerodynamic behavior of the FishBAC concept. Nomenclature
Tensile and flexural characteristics of corrugated laminate panels were studied using numerical and analytical methods and compared with experimental data. Prepreg laminates of glass fiber plain woven cloth were hand-laid by use of a heat gun to ease the creation of the panel. The corrugated panels were then manufactured by using a trapezoidal machined aluminium mould. First, a series of simple tension tests were performed on standard samples to evaluate the material characteristics. Next, the corrugated panels were subjected to tensile and three-point bending tests. The force-displacement graphs were recorded. Numerical and analytical solutions were proposed to simulate the mechanical behavior of the panels. In order to model the energy dissipation due to delamination phenomenon observed in tensile tests in all members of corrugated core, plastic behavior was assigned to the whole geometry, not only to the corner regions. Contrary to the literature, it is shown that the three-stage mechanical behavior of composite corrugated core is not confined to aramid reinforced corrugated laminates and can be observed in other types such as fiber glass. The results reveal that the mechanical behavior of the core in tension is sensitive to the variation of core height. In addition, for the first time, the behavior of composite corrugated core was studied and verified in bending. Finally, the analytical and numerical results were validated by comparing them with experimental data. A good degree of correlation was observed which showed the suitability of the finite element model for predicting the mechanical behavior of corrugated laminate panels.
Coated composite corrugated panels have wide applications in engineering, especially in morphing skins where extreme anisotropic stiffness properties are required. The optimal design of these structures requires high-fidelity models of the panels that would be incorporated into multi-disciplinary system models. Therefore, numerical and experimental investigations are required that retain the dependence on the nonlinear static and dynamic behavior of these structures. Considering the nonlinear effects due to the material properties and mechanism of deformation, the mechanical behavior of composite corrugated laminates with elastomeric coatings is studied in this paper by means of numerical and experimental investigations. The importance of this work is that it provides detailed experimental and numerical models of the panel that can be used for further static and dynamic homogenization and optimization studies. In this regard, an investigation of the manufacturing method and an evaluation of the mechanical characteristics of the materials are presented. Then the tensile, hysteresis and three-point bending tests of the coated corrugated panels are analyzed and the mechanical behavior of the panel is simulated. The comparison studies demonstrate the accuracy of the finite element model to predict the mechanical behavior of the coated corrugated panels. Finally, two concepts to deal with the non-smooth surface of the panel during bending for the morphing skin application are proposed.
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