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In this paper, an equivalent model on coefficient of hygrothermal expansion for composite layer and a multi-scale model for calculating the strain and stress of composite plates are proposed. These two models also can be applied to thermal expansion problems and guide the structure design of the composite materials. A model descripting the coupling behavior of moisture diffusion and stress in composite laminates is proposed based on the second Fick’s law. Compared to other models, this model can accurately predict the anomalous behavior in the process of moisture absorption. A number of experiments and finite-element simulations are conducted to validate this model. A comparison of the model’s predictions with experimental data shows a good agreement. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops a multi-stable lattice structure consisting of tri-stable lattice cell which is made by bistable laminates. The multi-stable lattice structure with N tri-stable lattice cells, which can exhibit 2 N stable states, is successfully designed and fabricated. The critical loads snapping lattice structure are investigated by the experimental and finite element techniques. The method to simulate the behaviors of contact and constraint between the neighboring bistable laminates are presented. The snap through process of multi-stable lattice structures among multiple states are numerically simulated and experimentally validated. The multiple stabilities highlight the potential to achieve a smooth shape variation in the large area multi-stable structures. [Copyright &y& Elsevier]

Bi-stable composite laminates with piezoelectric transducers have been shown to capture energy over a wide frequency range and deliver significantly greater energy than resonant devices. In this work, the influence of lay-up design on the performance of bi-stable piezoelectric energy harvester (BPEH) based on bi-stable hybrid symmetric laminate (BHSL) is analyzed and verified. The initial voltage induced by stable configuration and longitudinal curvature of BPEH with different lay-up and hybrid width were calculated and analyzed by a static finite element analysis. The lay-up can vary initial voltage and longitudinal in opposite directions, and hybrid width can adjust these two variables in the same direction. The strain variations of piezoelectric transducer between two stable configurations were also analyzed. The initial voltage of BPEH depends on strain variations in the two directions. And then the finite element results are verified by experiment. Three types of BPEH were manufactured and actuated by two methods to measure their output powers. These BPEHs presented different dynamic responses, and the output powers under different vibration modes were measured. The highest output power of BPEH in this work is 42.2 mW and the highest power density is 78.1 mW/cm 3 . [ABSTRACT FROM AUTHOR]

Bistable composite laminates have the potential advantage in the fields of wind energy harvesting and deformable wings, which involve many fluid–structure interaction issues. This paper presents the fluid–structure interaction analysis of a cantilevered bistable hybrid symmetrical laminate (BHSL) in the uniform wind. In this work, a finite element model based on the Lattice Boltzmann Method (LBM) is used to analyze the wind-induced response of the BHSL and its variations with respect to wind speed and laminate length. Then, the wind-induced vibration behavior of BHSL is verified by wind tunnel tests. The finite element analysis (FEA) results are in good agreement with the experimental results. The results show that as the wind speed increases, the BHSL transitions from a single-well vibration response to a cross-well vibration response. The wind-induced vibration analysis of BHSL will provide analytical methods for its application in deformable wings and energy harvesting for wind-induced vibration. [ABSTRACT FROM AUTHOR]

A micromechanical model to predict the stress relaxation of composite bolted connections based on viscoelastic theory has been presented. A number of experiments were conducted to validate the model. The influence of the initial clamp forces and the plate thicknesses of GFRP and CFRP on the stress relaxation were investigated. The stress relaxation predicted showed a good agreement with the experimental data with the deviation of about 6%. It shows that there exists a certain time, which is approximately 5 times of the relaxation time, and the contribution of the composites’ viscoelasticity could be ignored when the time is greater than the certain time. The loss of the clamp forces was primarily caused by the increase in plasticity. [ABSTRACT FROM AUTHOR]

This paper focuses on a study of the snap-through behavior of a family of bi-stable plates constructed by hybrid symmetric laminates with a cantilever boundary. Involving shape change and actuation demand, a deep understanding of the snap-through behavior is of particular importance since this bi-stable laminate is often served as a host structure of energy harvester or a morphing structure. The snap-through behavior is obtained using two displacement-controlled finite element procedures provided in the commercial software ABAQUS and the results are verified by experiments. The entire equilibrium path of reaction force-displacement response with a couple of zero load crossings is captured by the 'Static, Riks' procedure to reveal the potential nonlinear structural behavior. The practical situation of the reaction force-displacement curve is obtained by the 'Static, General' procedure which exhibits consistent results with experiments. Several characteristics, such as snap-down, hysteresis, negative stiffness, and even zero stiffness are captured. A parametric study including lay-up design and length is also carried out using the finite element model and verified by experiments. The results show that the lay-up design not only can fundamentally change the snap-through response but also influences other characteristics of this bi-stable laminate including stable shape, and the length is a relatively reliable parameter to alter the snap-through features, e.g. peak force and hysteresis performance. [ABSTRACT FROM AUTHOR]

The resulting oscillation of bi-stable hybrid symmetric laminate could enable broadband energy harvesting via piezoelectric transduction. The aim of this work is to investigate its dynamic behaviors to provide the basis for designing broadband energy harvester. This paper proposes the dynamic analysis of this bi-stable laminate, focusing on the intra-well dynamics around its stable states and the inter-well dynamics between two stable states. Two types of stacking sequence are performed for this bi-stable laminate, and experimental testing with different harmonic excitations is carried out for each type of this bi-stable laminate. The strain responses at three positions are monitored to investigate the dynamic responses. A finite element model is also developed to analyze the static strain distribution and capture the dynamics. The results show that the laminates exhibit intra-well response under low-level excitation, and the inter-well response at a particular range frequency appears when excitation level increases. Different types of inter-well response mode involving the snap-through behavior are obtained in experiments, such as intermittent inter-well vibration and chaotic vibration. The presented results essentially highlight the need for considering the stacking sequence associated with the dynamics while designing the hybrid bi-stable symmetric laminate to obtain the desirable nonlinear response. [ABSTRACT FROM AUTHOR]

A bi-stable device is presented for simultaneous vibration absorption and energy harvesting by introducing the piezoelectric element into the bi-stable nonlinear energy sink (BNES), which is called the bi-stable piezoelectric absorber (BPZA). BPZA only consists of the cantilever bi-stable piezoelectric composite laminate (BPCL) and tip masses. This BPZA is a lightweight, simple and reliable structure since it does not need any external devices to maintain bistability. A finite element model (FEM) and an equivalent theoretical model are developed to model a harmonically excited linear oscillator coupled with BPZA. The Runge-Kutta method is used to solve the theoretical model numerically. The effects of the excitation amplitude, the tip mass of BPZA and the load resistance are considered on the vibration suppression efficiency and energy harvesting of BPZA. The results show adjusting these parameters can improve the vibration suppression efficiency and energy harvesting of BPZA. In addition, the experimental prototype is prepared and verifies the rightness of the finite element model and theoretical model. The BPZA achieves the goal of higher power density at lower acceleration and simultaneously has a good vibration absorption effect. Maximum power of 15.8mW is generated at an excitation frequency of 22 Hz and acceleration of 0.5 g. [ABSTRACT FROM AUTHOR]

The mechanical behaviors of the twisted profiled textile composite structures with different twist angles were studied by using a novel cantilever beam experiment. The strain distributions on the upper surface of the specimen were monitored by using DIC. Several strain gauges were located at different positions on the lower surface of the specimen. With the increase of cantilever load, the deformation of twisted specimen experienced from the initial torsion to the bending-torsion coupling deformation. The effects of twist angles on stiffness and strength of the twisted composite structures were analyzed. The stiffness distributions of the twisted composite structures are determined by using the finite element analysis (FEA) combining with the experimental results. There is a cubic polynomial function relationship between the macroscopic local twisted angle and the local material stiffness. The stiffness and strength of 135° twisted specimen are higher than that of 45°twisted specimen. The dominant failure mode was the compression fracture at the edge of the lower right corner of the twisted specimen. This study can be helpful of guiding the design of the twisted profiled textile composites structures. [ABSTRACT FROM AUTHOR]

The quasi-zero-stiffness (QZS) vibration isolator is usually composed of positive and negative stiffness elements in parallel. The negative stiffness element usually requires specific constraint boundaries to form negative stiffness characteristics, which cannot meet the lightweight design of spacecraft structures. So the bi-stable hybrid symmetric laminate (BHSL) is presented as a negative stiffness element. A finite element model (FEM) is developed to carry out static and dynamic analyses of this vibration isolator. An equivalent theoretical model is developed based on the restoring force–displacement curve of BHSL. The approximate analytical solutions and direct numerical solutions are obtained by employing the averaging method and the Runge-Kutta method, respectively. Different types of the steady-state response are obtained, namely the symmetrical multi-harmonic response, the asymmetric multi-harmonic response and the single-harmonic response. There exists a small gap between the analytical solutions and the Runge-Kutta solutions or the FEM results only at the low frequency excitation due to the super-harmonics. The displacement transmissibility is used to quantify the vibration isolation performance of this vibration isolator. The experiment is designed to verify the theoretical and FEM models from static and dynamic analysis perspectives. The results show adjusting geometric parameters and lay-up designs can improve the vibration isolation performance. [ABSTRACT FROM AUTHOR]

Tool-part interaction during the manufacture of the bistable composite shells with initial curvature is inevitable, which has a noticeable influence on stable configurations. The effect of tool-part interaction is considered by introducing a shear layer whose parameters are determined by a series of experiments. This paper develops an analytical model with shear layer effect based on the Rayleigh-Ritz model to capture the configuration variation with bistable composite shell with initial curvature. The model reveals the rule of curvature change in different radii and plies, which provides a criterion for the existence of bistability. The results show tool-part interaction has a significant influence on thin bistable composite shells with initial curvature whose prediction accuracy is improved. The analytical predictions are verified by results based on the experiments and finite element models. Moreover, the influences of initial radius, cross-section angle, stacking sequence, and twisting response are analyzed. The twist behavior of two stable configurations is investigated, which can provide a guide for designing the bistable composite structures. [ABSTRACT FROM AUTHOR]