Fuhong Dai

The morphing bi-stable glass fiber–reinforced polymer laminates actuated by embedded electrothermal alloy:

This article develops and proves the concept of morphing bi-stable glass fiber–reinforced polymer laminates using electrothermal alloys to trigger the snap-through from one stable configuration to another. The presented concept considers an alternative to existing morphing bi-stable concepts wherein actuators are used to elastically actuate bi-stable laminates to snap between stable configurations. These existing concepts are restricted to some bi-stable laminates with certain layups and sizes. For the concept discussed here, the electrothermal alloys are embedded in the laminates and are used as internal heating sources. Morphing can be achieved by heating and subsequently cooling the local region of the laminate, and no energy is needed to maintain the deformation. One-way and a two-way morphing bi-stable laminates are designed and manufactured. The finite element simulation is performed to predict the thermally induced morphing process. The experimental morphing process is compared with the simulated process, and good agreement between experiments and predictions is found. The basic principle of this morphing bi-stable structure is discussed. Based on the same principle, more different forms of morphing bi-stable structures can be designed and manufactured.

Cured Shapes of Bi-stable CFRP Composite Laminates with the Side Length Exceeding a Critical Value

Curvature saturation has been observed in bi-stable composite laminates when the side length exceeds a critical value. This is the curvature which the stable cylindrical shell converges to after cooling down. Conventional models of the displacement field fail to predict the correct shapes. This is especially true when the laminate forms a wound-up cylinder which can occur when the longer side is several times the critical length. This paper presents a saturated curvature model to predict the cured shape for bi-stable laminates. The finite element analysis is also carried out to capture the cured shape. Both the analytical model and finite element method give the accurate cured shape. The cured shapes are measured experimentally. The results from the proposed model and finite element analysis are compared with the experimental and show a good agreement.

Static aeroelastic deformation of flexible skin for continuous variable trailing-edge camber wing

The method for analyzing the static aeroelastic deformation of flexible skin under the air loads was developed. The effect of static aeroelastic deformation of flexible skin on the aerodynamic characteristics of aerofoil and the design parameters of skin was discussed. Numerical results show that the flexible skin on the upper surface of trailing-edge will bubble under the air loads and the bubble has a powerful effect on the aerodynamic pressure near the surface of local deformation. The static aeroelastic deformation of flexible skin significantly affects the aerodynamic characteristics of aerofoil. At small angle of attack, the drag coefficient increases and the lift coefficient decreases. With the increasing angle of attack, the effect of flexible skin on the aerodynamic characteristics of aerofoil is smaller and smaller. The deformation of flexible skin becomes larger and larger with the free-stream velocity increasing. When the free-stream velocity is greater than a value, both of the deformation of flexible skin and the drag coefficient of aerofoil increase rapidly. The maximum tensile strain of flexible skin is increased with consideration of the static aeroelastic deformation.

A Morphing Bi-Stable Composite Laminate Actuated by Electric Heating Method

As the “morphing” or “shape adaptive” structural systems are getting considerable attention, a practical realization of a morphing needs substantial effort. This study proposes a concept of morphing bi-stable composite laminate. The morphing bi-stable laminate is locally embedded with electric heating material and has two stable states. The embedded heating material can elevate the temperature and relieve the thermal stress of the region heated by it. With this heating actuation method, an appropriate embedment of heating materials will enable the bi-stable laminate a morphing structure. This morphing bi-stable laminate can transform from one stable state to the other stable state by the heating effect of its heating composition. The FEA of the morphing process of this morphing bi-stable laminate was performed, and the critical temperature of the snap-through phenomenon was predicted. Experiment was conducted to verify the morphing process of this morphing bi-stable laminate, good agreement between the experiment and the FEA results are obtained.Copyright

Study on a new concept of multi-stable lattice structure

A new multi-stable lattice structure which is assembled by rectangular bi-stable composite laminates is designed. The snap-through of rectangular cross-ply composite laminates and a lattice structure is numerically and experimentally studied. The experiments to measure the snapping force levels of rectangular laminates and lattice structures are conducted. A method based on commercial software ABAQUS to simulate the snap-through behaviors of lattice structures is presented. Snap through of lattice structures are successfully described with the use of this method. The same phenomenon between the FEA and experiments are observed. The predicted curvatures show a good agreement with experimental results while there are some errors between predicted and measured critical loads.