Iman Dayyani

A review on shape memory alloys with applications to morphing aircraft

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.

Numerical and Experimental Investigations on Mechanical Behavior of Composite Corrugated Core

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.

The mechanical behavior of composite corrugated core coated with elastomer for morphing skins

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.

Fluid/Structure-Interaction Analysis of the Fish-Bone-Active-Camber Morphing Concept

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 the 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 str...

The design of a coated composite corrugated skin for the camber morphing airfoil

One of the critical components of a morphing wing is the anisotropic skin, which has to be stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. This work presents the design of an elastomer coated composite corrugated skin for the camber morphing airfoil. The good in-plane strain capability and highly anisotropic behaviour of composite corrugated panels make them very effective in morphing wing applications. The behaviour of these corrugated skins must be investigated comprehensively and optimized in terms of aero-elastic effects and the boundary conditions arising from the internal wing structure. In this article, the geometric parameters of the coated composite corrugated panels are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the corrugated skin. A finite element code for thin beam elements is used with the aggregate Newton’s method to optimize the geometric parameters of the coated corrugated panel. The advantages of the corrugated skin over the elastomer skin for the camber morphing structure are discussed. Moreover, a finite element simulation of the internal structure with the corrugated skin is performed under typical aerodynamic and structural loadings to check the design approach.

The Design of a Corrugated Skin for the FishBAC Compliant Structure

The curvature of an airfoil has a significant effect on the generated aerodynamic forces. Researchers have long pursued continuous changes to airfoil camber as an alternative to discrete trailing edge flaps with the potential to significantly reduce drag. The critical components of such morphing structures are mainly the compliant internal structure and an anisotropic skin, both of which have to be stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. In terms of the internal structure, the investigated design employs a variation of the biologically inspired compliant structure known as the FishBAC to create large continuous changes in airfoil camber and section aerodynamic properties. In terms of the skin, the highly anisotropic behavior of composite corrugated panels is very effective in morphing wing applications where the panels are stiff along the corrugations to withstand the aerodynamic loads and flexible transverse to the corrugations to allow deformation. Recently, the static behaviour of composite corrugated panels has been investigated independently of the internal wing structure through experimental analysis, numerical simulations and analytical equivalent modelling. However, as a proposed candidate for the skin of a morphing wing, the behaviour of these corrugated panels must be investigated comprehensively and optimized in terms of aeroelastic effects and the boundary conditions arising from the internal wing structure. In this paper, the geometric parameters of the coated composite corrugated panels are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the corrugated skin. The effect of the stringers of the FishBAC as the boundary conditions for the elastomer coated corrugated panel is considered in the optimization process. A finite element code for thin beam elements is used with the aggregate Newton based method to optimize the geometric parameters of the coated corrugated panel.

Hyperelastic tension of graphene

In this paper, we investigate the hyperelastic tensile behaviour of single layer graphene sheets (SLGSs). A one-term incompressible Ogden-type hyperelastic model is chosen to describe the mechanical response of C-C bonds. By establishing equality between the Ogden strain-energy and the variation of the Tersoff-Brenner interatomic potential, three different geometries of SLGSs are studied under tensile loading. We compute the Youngs modulus, the finite-deformation Poissons ratio, ultimate strains, total reactions, and the variation of the potential energy per carbon atom for large strains. Numerical simulations are compared with results obtained by molecular mechanics and molecular dynamics simulations, finite elements, continuum mechanics theory, and experiments. Our predictions are validated, revealing the potential predictive capabilities of the present hyperelastic framework for the analysis of graphene in the context of infinitesimal and large deformations. The good agreement found between our calcu...

Development and Testing of a Corrugated Skin for a Camber Morphing Aerofoil

This work presents the development and testing of a corrugated skin for the Fish Bone Active Camber (FishBAC) morphing airfoil concept. This novel biologically inspired morphing structure consists of a compliant skeletal core composed of a thin chord wise bending beam with periodic stringers, a compliant external skin structure and an actuation mechanism. One of the critical components of this morphing structure is the anisotropic skin which has to be stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. The good in-plane strain capability and highly anisotropic behavior of composite corrugated panels makes them very effective in morphing wing applications where the panels are stiff along the corrugations to withstand the aerodynamic loads and flexible transverse to the corrugations to allow deformation. Recently, the static behaviour of composite corrugated panels has been investigated independently of the internal wing structure through experimental analysis, numerical simulations and analytical equivalent modeling. However, as a proposed candidate for the skin of a morphing wing, the manufacturability of the corrugated panels and the feasibility of integration must be investigated comprehensively with different materials. Hence, the paper is structured in three parts. The first part gives a summary of the geometric parameters of the corrugated panels that are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the corrugated skin. The second part is mainly focused on the development of the composite corrugated skin using commercially available Kevlar. Finally, standard tensile tests were performed on the manufactured corrugated samples to evaluate their material characteristics. The advantages of the proposed technique used for the composite corrugated skin manufacture for the FishBAC morphing structure are discussed.