Yuying Xia

Variable stiffness biological and bio-inspired materials

This article reviews the main mechanisms of stiffness variation typically found in nature. The temporal changes in stiffness may be fully or partially reversible, or completely irreversible, and can be very slow or fast in time depending on the strategy adopted to alter the mechanical properties. It is also possible to observe changes in the stiffness in order to recover the original mechanical properties in damaged natural materials by means of self-healing mechanisms. In addition to stiffness variations in time, natural materials can also exhibit stiffness changes in space. These variations can be represented by alterations in the spatial distribution of the microscopic constituents across multiple hierarchical scales, from very small physical scales to large macroscopic dimensions. In order to optimise the strength and multifunctionality of these materials, spatial changes can also occur over larger areas at one single scale. In addition, several examples are provided to illustrate how natural materials have been exploited further in order to develop new bio-inspired materials.

The effect of corrugated skins on aerodynamic performance

Corrugated skins provide a good solution to morphing wings due to their highly anisotropic behavior. If the low stiffness corrugation plane is aligned in the chordwise direction, the airfoil shape change is possible. In contrast to the traditional smooth skin of an airfoil, a corrugated skin influences both the local and global aerodynamics of a wing. The aim of this study is to investigate the effect of a corrugated skin on the global aerodynamics of an airfoil, particularly lift and drag characteristics. First, the aerodynamic analysis of a NACA 0012 airfoil with a smooth profile is conducted, both in the wind tunnel and by computational fluid dynamics, at different Reynolds numbers and compared to the data in the literature. The lift and drag coefficients at different angles of attack, between −10° and 10°, are considered. Next, two NACA 0012 airfoils with different sized corrugated profiles are investigated both experimentally and by numerical simulation. The effects of corrugation size and Reynolds number are analyzed and quantified relatively to the standard NACA0012 airfoil with a smooth skin. Preliminary numerical results are validated using the experimental data.

Equivalent models of corrugated laminates for morphing skins

The design of the skins has been identified as a major issue for morphing aircraft wings. Corrugated laminates provide a good solution due to their extremely anisotropic behavior. However, the optimal design of a morphing aircraft requires simple models of the skins that may be incorporated into multi-disciplinary system models. This requires equivalent material models that retain the dependence on the geometric parameters of the corrugated skins. An analytical homogenization model, which could be used for any corrugation shape, is suggested in this paper. This method is based on a simplified geometry for a unit-cell and the stiffness properties of original sheet. This paper investigates such a modeling strategy and demonstrates its performance and potential.

Efficient solution of the fuzzy eigenvalue problem in structural dynamics

Purpose – Many analysis and design problems in engineering and science involve uncertainty to varying degrees. This paper is concerned with the structural vibration problem involving uncertain material or geometric parameters, specified as fuzzy parameters. The requirement is to propagate the parameter uncertainty to the eigenvalues of the structure, specified as fuzzy eigenvalues. However, the usual approach is to transform the fuzzy problem into several interval eigenvalue problems by using the α-cuts method. Solving the interval problem as a generalized interval eigenvalue problem in interval mathematics will produce conservative bounds on the eigenvalues. The purpose of this paper is to investigate strategies to efficiently solve the fuzzy eigenvalue problem. Design/methodology/approach – Based on the fundamental perturbation principle and vertex theory, an efficient perturbation method is proposed, that gives the exact extrema of the first-order deviation of the structural eigenvalue. The fuzzy eigen...

Estimating Mechanical Properties of Bi-continuous Two-Phase Composites for Optimised Multi-functionality

Composites with multiple (bi-) interpenetrating phases are ideally placed to realise multi-functionality and certain multifunctional and smart materials may be modeled as bi-continuous two-phase composites. This paper estimates the mechanical properties of such materials using finite element analysis and homogenization. The effect of phase volume fraction and contiguity on the properties is investigated for a range of microstructures with triply periodic minimal P interfaces between the two phases. The results show that the properties of the composite depend on not only the overall volume fraction but also the contiguity of the constituent phases.

Development of a morphing wingtip based on compliant structures

Compliant structures, such as flexible corrugated panels and honeycomb structures, are promising structural solutions for morphing aircraft. The compliant structure can be tailored to carry aerodynamic loads and achieve the geometry change simultaneously, while the reliability of the morphing aircraft can be guaranteed if conventional components and materials are used in the fabrication of the morphing structure. In this article, a compliant structure is proposed to change the dihedral angle of a morphing wingtip. Unsymmetrical stiffness is introduced in the compliant structure to induce the rotation of the structure. Trapezoidal corrugated panels are used, whose geometry parameters can be tailored to provide the stiffness asymmetry. An equivalent model of the corrugated panel is employed to calculate the deformation of the compliant structure. To provide the airfoil shape, a flexible honeycomb structure is used in the leading and trailing edges. An optimisation is performed to determine the geometry variables, while also considering the actuator requirements and the available space to instal the compliant structure. An experimental prototype has been manufactured to demonstrate the deformation of the morphing wingtip and conduct basic wind tunnel tests.