Search Results (15)

The bistable laminated structure is widely used in many fields due to its unique deformation characteristics. In practical engineering, laminates under different structural constraints will exhibit different steady-state deformation characteristics. This study proposes a novel bistable laminated structure based on applying a variable-stiffness design to the deformation element. By adjusting the laying area of the metal layer in the variable-stiffness zone, the out-of-plane deformation and local curvature distribution can be changed to better meet application requirements. This study adopts the finite element numerical simulation method to systematically investigate the influence of geometric parameters, the proportion of metal layer edge length, and the number of layers on the deformation performance of bistable laminates. Considering the design of a flexible bistable variable-camber wing, the variable-stiffness design proposed in this study was adopted to coordinate the curvature distribution of laminates, making the cambered airfoil of the wing more uniform and smoother and improving aerodynamic efficiency. The research results not only provide new ideas for designing bistable laminates under complex constraints but also offer design references for the lightweight optimization and aerodynamic performance improvement of bistable morphing wings. Full article

A bistable effect on a laminate structure with a piezoelectric patch was tested to harvest kinetic energy. The composite bistable plate was prepared in the autoclave with two different orientations of the glass fibers. The dynamic tests were performed on the universal testing machine using cyclic vertical compression excitation. During the tests, the bottom edge of the plate was clamped firmly while its upper edge was attached with some clearance to enable sliding. In such a configuration, the friction force between the plate and upper clamp element is responsible for the plate excitation. Simultaneously, the plate has enough space to change the shape between the two equilibria. During the harmonic excitation of the testing machine operating mode, a piezoelectric element was placed on the bistable plate and its voltage and normalized power outputs were evaluated. The experiments were repeated with additional mass distribution, which influenced the natural frequency of the plate. Full article

Material properties, geometrical dimensions, and environmental conditions can greatly influence the characteristics of bistable composite laminates. In the current work, to understand how each input feature contributes to the curvatures of the stable equilibrium shapes of bistable laminates and the snap-through force to change these configurations, the correlation between these inputs and outputs is studied using a novel explainable artificial intelligence (XAI) approach called SHapley Additive exPlanations (SHAP). SHAP is employed to explain the contribution and importance of the features influencing the curvatures and the snap-through force since XAI models change the data into a form that is more convenient for users to understand and interpret. The principle of minimum energy and the Rayleigh–Ritz method is applied to obtain the responses of the bistable laminates used as the input datasets in SHAP. SHAP effectively evaluates the importance of the input variables to the parameters. The results show that the transverse thermal expansion coefficient and moisture variation have the most impact on the model’s output for the transverse curvatures and snap-through force. The eXtreme Gradient Boosting (XGBoost) and Finite Element (FM) methods are also employed to identify the feature importance and validate the theoretical approach, respectively. Full article

Deployable extendable booms are widely used in aerospace technology due to many advantages they have, such as high folded-ratio, lightweight and self-deployable properties. A bistable FRP composite boom can not only extend its tip outwards with a corresponding rotation speed on the hub, but can also drive the hub rolling outwards with a fixed boom tip, which is commonly called roll-out deployment. In a bistable boom’s roll-out deployment process, the second stability can keep the coiled section from chaos without introducing a controlling mechanism. Because of this, the boom’s roll-out deployment velocity is not under control, and a high moving speed at the end will give the structure a big impact. Therefore, predicting the velocity in this whole deployment process is necessary to be researched. This paper aims to analyze the roll-out deployment process of a bistable FRP composite tape-spring boom. First, based on the Classical Laminate Theory, a dynamic analytical model of a bistable boom is established through the energy method. Afterwards, an experiment is introduced to produce some practical verification for comparison with the analytical results. According to the comparison with the experiment, the analytical model is verified for predicting the deployment velocity when the boom is relatively short, which can cover most booms using CubeSats. Finally, a parametric study reveals the relationship between the boom properties and the deployment behaviors. The research of this paper will give some guidance to the design of a composite roll-out deployable boom. Full article

Bistable or multi-stable structures have found broad applications in the fields of adaptive structures, flow control, and energy harvesting devices due to their unique nonlinear characteristics and strong local stability behavior. In this paper, a theoretical model based on the principle of minimum potential energy and the Rayleigh–Ritz method is established to study the dynamic characteristics of a bistable unsymmetric laminate with a fixed center. Numerical results of this theoretical model were obtained and verified by an FEA model using ABAQUS. The nonlinear dynamic characteristics and the structural response under different levels of external excitation were investigated and verified by experiments. The realization conditions of single-well vibration and cross-well vibration of bistable laminates were determined, with which the actuation strategies can be optimized for targeting modal frequencies of bistable laminates. Full article

For the last three decades, bistable composite laminates have gained publicity because of their outstanding features, including having two stable shapes and the ability to change these states. A common challenge regarding the analysis of these structures is the high computational cost of existing analytical methods to estimate their natural frequencies. In the current paper, a new methodology combining the Finite Element Method (FEM) and Multi-Objective Genetic Programming (MOGP) is proposed for the analysis of bistable composite structures, leading to some analytical relations derived to obtain the modal parameters of the shells. To achieve this aim, the data extracted from FEM, consisting of the ratio of the length to width (a/b) and the thickness (t) of the laminate, is split into Train and Validation, and Test, subsets. The former is used in MOGP, and four formulas are proposed for the prediction of the free vibration parameters of bistable laminates. The formulas are checked against the Test subset, and the statistical indices are calculated. An excellent performance is observed for all GP formulas, which indicates the reliability and accuracy of the predictions of these models. Parametric studies and sensitivity analyses are conducted to interpret the trend of input parameters in the GP models and the level of sensitivity of each natural frequency formula to the input parameters. These explicit mathematical expressions can be extended to the other bistable laminates to obtain their natural frequencies on the basis of their geometrical dimensions. The results are validated against the experimental data and verified against FEM outcomes. Full article

Bistable polymer composite structures are morphing shells that can change shape and maintain two stable configurations. At present, mainly two types of bistable polymer composite structures are being studied: cross-ply laminates and antisymmetric cylindrical shells. This paper proposes a unified semianalytical model based on the extensible deformation assumption and nonlinear theory of plates and shells to predict bistability. Moreover, the higher-order theoretical model is extended for better prediction accuracy, while the number of degrees of freedom is not increased; this ensures a lower computational cost. Finally, based on these theoretical models, the main factors affecting the stable characteristic of the two bistable polymer composite structures are determined by comparing the models of various orders. The main challenges in describing the bistable behavior, such as bifurcation points and the curvatures of stable states, are addressed through prediction of the corner transversal displacement in stable configurations. The results obtained from the theoretical model are validated through nonlinear finite element analysis. Full article

This paper proposes a multi-objective optimization model for anti-symmetric cylindrical shell in the bionic gripper structure. Here, the response surface method is used to establish multiple surrogate models of the anti-symmetric cylindrical shell, and the non-dominated sorting genetic algorithm-II (NSGA-II) is used to optimize the design space of the anti-symmetric cylindrical shell; the design points of the anti-symmetric cylindrical shell are verified by experimental methods. The optimization goals are that the first steady state transition load (the transition process of the bionic gripper structure from the open state to the closed state) of the anti-symmetric cylindrical shell is minimized, and the second steady state transition load (the transition process of the bionic gripper structure from the closed state to the open state) is the largest. At the same time, in order to prevent stable instability caused by stress concentration in the second steady state of the anti-symmetric cylindrical shell, the maximum principal plane stress is given as the constraint condition. The validity of the optimization results is verified by finite element and experimental methods. Due to the stable transition load of the anti-symmetric cylindrical shell being significantly larger than that of the orthogonal laminated plate, therefore, the anti-symmetric cylindrical shell has potential application prospects in the application of deformable structures and bionic structures that require composite functions such as having light weight, high strength, and large clamping force. The novelty of this paper lies in the multi-objective optimization of the application of the antisymmetric bistable cylindrical shell in the bionic gripper structure. Full article

Bistable energy harvesters have been extensively studied. However, theoretical research on the dynamics of bistable energy harvesters based on asymmetric bistable composite laminated plate and shell structures has not been conducted. In this paper, a theoretical model on the dynamics of an energy harvester based on an asymmetric bistable composite laminated shell is established. The dynamic snap-through, the nonlinear vibrations and the voltage output with two potential wells of the bistable energy harvester are studied. The influence of the amplitude and the frequency for the base excitation on the bistable energy harvester is studied. When the frequency for the base excitation with a suitable amplitude in the frequency sweeping is located in a specific range or the amplitude for the base excitation with a suitable frequency in the amplitude sweeping is located in a specific range, the large-amplitude dynamic snap-through, nonlinear vibrations and voltage output with two potential wells can be found to occur. The amplitude and the frequency for the base excitation interact on each other for the specific amplitude or frequency range which migrates due to the softening nonlinearity. The vibration in the process of the dynamic snap-through behaves as the chaotic vibration. The nonlinear vibrations of the bistable system behave as the periodic vibration, the quasi-periodic vibration and the chaotic vibration. This study provides a theoretical reference for the design of energy harvesters based on asymmetric bistable composite laminated plate and shell structures. Full article

As bistable composite laminated plate and shell structures are often exposed to dynamic environments in practical applications, the global and local dynamics of a bistable asymmetric composite laminated shell subjected to the base excitation is presented in this paper. Temperature difference, base excitation amplitude, and detuning parameters are discussed. With the change of temperature difference, the super-critical pitchfork bifurcation occurs. Three equilibrium solutions corresponding to three equilibrium configurations (two stable configurations and one unstable configuration) can be obtained. With the increase of excitation amplitude, local and global dynamics play a leading role successively. The global dynamics between the two stable configurations behave as the periodic vibration, the quasi-periodic vibration, the chaotic vibration and dynamic snap-through when the excitation amplitude is large enough. The local dynamics that are confined to a single stable configuration behave as 1:2 internal resonance, saturation and permeation when the excitation amplitude is small. Dynamic snap-through and large-amplitude vibrations with two potential wells for the global dynamics will lead to a broad application prospect of the bistable asymmetric composite laminated shell in energy harvesting devices. Full article

The nonlinear behaviors and energy harvesting of an unsymmetric cross-ply square composite laminated plate with a piezoelectric patch is presented. The unsymmetric cross-ply square composite laminated plate has two stable equilibrium positions by applying thermal stress, thus having snap-through with larger amplitude between the two stable equilibrium positions relative to the general laminated plate. Based on the von-Karman large deformation theory, the nonlinear electromechanical coupling equations of motion of the unsymmetric composite laminated plate with a piezoelectric patch are derived by using Hamilton’s principle. The influence of the base excitation amplitude on nonlinear behaviors and energy harvesting are investigated. For different base excitation amplitudes, the motions of the system demonstrate periodic motion, quasi-periodic motion, chaotic motion and snap-through, and two single-well chaotic attractors and a two-well chaos attractor coexist. Moreover, the power generation efficiency is optimal when the excitation amplitude is in a certain range due to its own unique nonlinear characteristics. The unsymmetric cross-ply square composite laminated plate subjected to thermal stress can actually be called a kind of bistable composite shell structure that has a broad application prospect in combination with morphing aircraft, large deployable antenna and solar panel, which are very likely to have nonlinear vibration. Full article

Multistable structures that possess more than one elastically stable equilibrium state are highly attractive for advanced shape-changing (morphing) applications due to the nominal control effort required to maintain the structure in any of its specific stable shapes. The aim of the paper is to develop a bistable cross-shaped structure consisting of symmetric and unsymmetric laminate actuated using Macro Fibre Composite (MFC) actuators. The critical snap-through voltages required to change the shapes are investigated in a commercially available finite element package. The use of MFC actuators to snap the bistable laminate from one equilibrium shape to another and back again (self-resetting) is demonstrated. A new cross-shaped design of active bistable laminate with MFC actuators is proposed where the cross-shape consist of four rectangles on the four legs and a square on the middle portion. All the rectangles are made up of unsymmetric laminates, and the central portion is designed with a symmetric laminate. MFC actuators are bonded on both sides of the four legs to trigger snap-through and snap-back actions. An attempt is made to address the possible design difficulties arising from the additional stiffness contribution by MFC layers on the naturally cured equilibrium shapes of cross-shaped bistable laminates. Full article

Morphing structures suitable for unmanned aerial vehicles (UAVs) have been investigated for several years. This paper presents a novel lightweight, morphing concept based on the exploitation of the “lever effect” of a bistable composite plate that can be integrated in an UAV horizontal tail. Flight dynamics equations are solved in Simulink environment, thus being able to simulate and compare different flight conditions with conventional and bistable command surfaces. Subsequently, bistable plates are built by using composite materials, paying particular attention to dimensions, asymmetric stacking sequence and total thickness needed to achieve bistability. NACA0011 airfoil is chosen for proving this concept. Wind tunnel tests demonstrate that the discrete surface is capable of withstanding the aerodynamic pressure. A remotely piloted vehicle is employed to test the discrete horizontal tail command during the take-off. The results show that, choosing a proper configuration of constraints, stacking sequence and aspect ratio for the bistable laminate, it is possible to tailor the snap-through mechanism. The proposed concept appears lighter and increases aerodynamic efficiency when compared to conventional UAV command surfaces. Full article

It has been found that certain asymmetric composite laminates exhibit bistability, where the composite laminate exhibits multiple stable static equilibrium states. If the bistable composite is actuated, it will snap to its secondary equilibrium state and then remain there without further actuation. This study investigates how the amount of symmetry in a combined symmetric asymmetric rectangular laminate under an imposed clamped edge boundary condition affects the bistability and the curvature of the laminate. Laminates with varying amounts of asymmetry were fabricated and then measured using a profilometer to capture the curvatures of the equilibrium shapes. The results showed that up to 20% symmetry can be introduced in the laminate without a substantial loss in snap through curvature, and that up to 83% symmetry can be introduced in the laminate before bistability is lost. Finite element simulations were conducted in Abaqus and showed good correlation with the experimental results. Full article

Shape-adaptive or morphing capability in both aerospace structures and wind turbine blade design is regarded as significant to increase aerodynamic performance and simplify mechanisms by reducing the number of moving parts. The underlying bistable behavior of asymmetric cross-ply composites makes them a suitable candidate for morphing applications. To date, various theoretical and experiential studies have been carried out to understand and predict the bistable behavior of asymmetric laminates and especially the curvature obtained in their stable configurations. However, when the bi-stable composite plate is integrated with shape memory alloy wires to control the curvature and to snap from a stable configuration to the other (shape memory alloy composite, SMAC), the identification of the design parameters, namely laminate edge length, ply thickness and ply orientation, is not straightforward. The aim of this article is to present the formulation of an optimization problem for the parameters of an asymmetric composite laminate integrated with pre-stressed shape memory alloys (SMA) wires under bi-stability and a minimum deflection requirement. Wires are modeled as an additional ply placed at the mid-plane of the composite host plate. The optimization problem is solved numerically in MATLAB and optimal design variables are then used to model the SMAC in ABAQUS™. Finite element results are compared against numerical results for validation. Full article