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In this paper, a bi-stable piezoelectric energy harvester based on the bi-stable hybrid composite laminate with a new stacking sequence design is proposed. The new stacking sequence enables this bi-stable energy harvester to have some unique features, such as uniform strains of piezoelectric elements and symmetric stable configurations. Meanwhile, the new stacking sequence design enhances the room to adjust its natural frequency such that this proposed harvester allows for adjusting to lower frequency range and increasing the inertia by a tip mass to lower the demand of excitation level in comparison to previous settings. A finite element analysis is developed to investigate the static and dynamic characteristics of this new bi-stable energy harvester. A simple numerical model with a modified version of the Duffing equation is developed based on the unique nonlinear restoring force obtained from finite element analysis to describe the fundamental response characteristics of this nonlinear bi-stable energy harvester. Numerical simulations and experiments are carried out at different harmonic excitation levels ranging from 10 to 40 Hz. The results verify that the proposed model can reasonably capture the dynamic characteristics of this broadband bi-stable energy harvester. The output powers were measured under different vibration patterns. Maximum power of 31.1 mW was generated under large-amplitude and high-energy orbits cross-well vibration pattern at an excitation frequency of 22 Hz and acceleration of 3 g ( g  = 9.8 m/s 2 ). [ABSTRACT FROM AUTHOR]

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]

A bi-stable piezoelectric energy harvester (BPEH) based on bi-stable hybrid symmetric laminate (BHSL) is proposed for energy harvesting. Due to its large deformation and low actuation, BPEH has better energy harvesting performance at low frequencies compared with traditional resonance cantilever-type energy harvester. Two types of stacking sequence and two types of piezoelectric ceramics (PZT) shapes with identical area were considered, and four types of BPEHs were designed. The stable configurations of the BPEHs and the stress states of PZT bonded on the surface of the BSHL were simulated and analyzed by finite element analysis. In addition, the four types of BPEHs were fabricated and experimentally evaluated. The BPEHs were actuated by hand shaking to transition between the two stable configurations. Using this method, the voltage outputs and power outputs were measured at two frequencies (2 Hz and 5 Hz). The results demonstrate that the BPEHs exhibited high output power because the PZTs on their surface were fully utilized due to their double curved shape and uniform deformations. The generated powers from the BPEHs were significantly higher than that observed from a similar sized cantilever-type piezoelectric harvester. Simultaneously, the influences of stacking sequence and shape of PZT on the energy harvesting performance were evaluated. The BPEHs with the second stacking sequence generated higher power than those of first stacking sequence, and the rectangular PZT performed better compared to the square. The measured maximum power output generated by the BPEH with the second stacking sequence and rectangular PZT was 37 mW at 5 Hz. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a bistable twisting CFRP-metal hybrid laminate which has an external isotropic metallic layer. Different from the pure unsymmetric CFRP laminate and the hybrid unsymmetric laminate with an inner metallic layer, the laminate presented can be transformed from one negative curvature to another negative curvature instead of from one negative curvature to another positive curvature. Their room temperature shapes can be a unique paraboloid shape, a twisted cylindrical shape, or a twisted cylindrical shape that can be snapped through to another twisted cylindrical shape. The cured shape of the hybrid laminate is studied using analytical, finite element and experimental techniques. The investigation is focused on the hybrid laminate with lay-up of [0/90/metal]T, and shows that the principal direction of cured curvature is 45°. The predicted cured shape and the snap-through loads agree well with experimental results. [Copyright &y& Elsevier]

This paper lays stress on the equilibrium configurations analysis of a bi-stable unit composed of two cantilever beams with lateral post-buckling deformations. Two equilibrium configurations of the unit are described by deformations of the cantilever beam which is subjected to a shear force and has a boundary condition of zero-twist at the cantilever end. An analytical model based on the perturbation method was established for accurate post-buckling analysis of the beams. Experiments and numerical studies validate the analytical solutions on slender beams. Geometric parameters analysis on beam deformations demonstrates the application and limitation of the theoretical model. Finally, a multi-stable structure assembled by such bi-stable unit is illustrated, whose shapes are predicated by the analytical method. These results can be used to guide the design of shape reconfigurable structures with adjustable mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, a concave-shaped unit composed of two thin-walled beams with cantilever boundary conditions is designed and fabricated. Forces are introduced through the two cantilever ends of the beams whose constraints are hinged joints to get a bi-stable axial or lateral buckled unit. Initial buckling deformations of the concave-shaped units are analyzed theoretically and numerically. Experimental and numerical methods are used to investigate the post-buckling deformations and snap-through behaviors, when the concave-shaped units are axial buckled or lateral buckled. In the case of completing downwards and upwards snapping processes, there is a hysteresis loop in the force–displacement curve for the bi-stable lateral buckled unit, while is not for the bi-stable axial buckled unit. Finally, the influence of transverse displacements and dimension parameters on the snap-through behaviors of the bi-stable lateral buckled units is studied by the simulation method. • A bi-stable lateral buckled unit is designed and fabricated. • There are two symmetric modes for the initial buckled concave-shaped unit. • Post-buckling and snap-through behaviors of the bi-stable units are investigated. • The energy dissipation capacities are influenced by beams parameters. • The assembly bi-stable units are good candidates for energy-related applications. [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]

Abstract: This paper presents a new heating actuation method to induce the snap-through phenomenon of bi-stable laminates by manipulating the residual stress in laminates. The mechanism of the heating actuation method is analyzed, and the snap-through process is simulated by the finite element method. The heating actuation experiments on two types of laminates with different stacking sequences are performed. Good agreement is obtained between the experimental data and the finite element analysis (FEA). Subsequently, the heating actuation method is applied to several different bi-stable laminates and investigated by FEA. The FEA results show that this heating actuation method is an effective way to induce the snap-through phenomenon of bi-stable laminates of different thicknesses, sizes and shapes. [Copyright &y& Elsevier]

The bistable composite is a deformable lightweight structure with two stable states, which are widely used in aerospace and space fields as deployment mechanisms and deformable structures. In this paper, a new application is proposed as an omnidirectional and directional radiation reconfigurable antenna based on a bistable composite tube. The antenna is prepared based on carbon fiber composite (CFRP) and glass fiber composite (GFRP) as the substrate and metal as the antenna layer co-cured. Mechanical behavior and material micro-interface analyses of the bistable structures are performed. Antennas of different materials and different layups are fabricated and analyzed. The results indicate that the designed antenna structure can be stabilized in the unfolded or stowed state without external support, unfolded into an omnidirectional antenna, and stowed into a directional antenna. The electromagnetic analysis is simulated and experimented to verify its performance as a multifunctional and reconfigurable antenna. Meanwhile, this bistable antenna possesses many advantages, including its lightweight, high storage ratio, and rapid reconfiguration, which make it an excellent candidate for satellite and spacecraft antennas. A bistable structure is a lightweight composite that can be deformed and has two stable forms. It is widely used in aerospace and space applications, mainly as a deployment mechanism and deformable structure. A new application direction is proposed, which is used as a multifunctional and reconfigurable antenna. The designed antenna has an ultra-high storage ratio and is ultra-lightweight because it uses carbon fiber composite materials. Due to the first design of a bistable antenna tube, the mechanical and electromagnetic properties of different fiber materials, and layups are simulated and experimentally analyzed, respectively. The results show that the designed metal hybrid antenna tube has two variable stable configurations, and the antenna energy radiation direction map and operating frequency can be switched. Meanwhile the structure can be expanded or stored within 1s. Configuration B is an ultra-wideband antenna with a bandwidth of 1 GHz. By controlling the parameter changes, the antenna frequency can be widened and used within the required range. Besides, the state B can reach a high storage ratio. The structure can be assembled on spacecraft and satellites as a versatile stowable and deployable antenna. [Display omitted] • A bistable composite antenna tube with two stable forms, which can transform into each other quickly. • The omnidirectional/directional patterns and operating frequency of the antenna can be switched. • The multi-function antenna is lightweight and can reach a high storage ratio. • Different composites and metal layups are studied to analyze their different mechanical and electromagnetic properties. [ABSTRACT FROM AUTHOR]

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]

Bi-stable composite shells with initial curvature have obtained much attention due to their lightweight and morphing. The twisting deformation after curing is induced by thermal residual stress generated during the manufacture of the bistable composite shells, which has a significant influence on the mechanical behavior and the cured shape of bistable composite shells with initial curvature. This paper put forward a method to control the twisting by introducing an adjustive angle. An analytical model is developed to capture the suit adjustive angle, which makes the bistable composite shells without twisting. The analytical predictions are verified by results based on the experiments and finite element results. Moreover, the effect of initial radius, ply angle, thermal expansion coefficients, and elasticity modulus on an adjustive angle is considered by the analytical model, which can provide a guide for designing the bistable composite structures without twisting. The curvatures after twisting control are provided to predict the configuration of bistable composite shells with initial curvature. • A method to control the twisting is presented by introducing an adjustive angle. • The bistable composite shells with initial curvature without twisting are obtained by twisting control. • The adjustive angle is directly proportional to the initial radius and has a nonlinearity to the ply angle. • The curvature of bistable composite shells with initial curvature without twisting is investigated. [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]

A nonlinear device is presented for simultaneous vibration absorption and energy harvesting. This device is composed of a nonlinear energy sink and a piezoelectric energy harvester (NES-EH), and its core component is the simply-supported bi-stable piezoelectric composite laminate (BPCL). Its outstanding advantages are light weight, simple and reliable structure. The theoretical model is developed to model a harmonically excited linear oscillator coupled with NES-EH. The Runge–Kutta method and the harmonic balance method (HBM) are used to solve the theoretical model numerically and analytically. The vibration suppression efficiency is utilized to quantify the vibration absorption performance, while the energy harvesting performance is assessed by bandwidth for energy harvesting and maximum voltage within the bandwidth. The effects of the excitation amplitude, the concentrated mass of NES-EH, the length and width of BPCL, and the load resistance are considered on the performances of NES-EH. The vibration absorption and energy harvesting performances of NES-EH can be improved by adjusting these parameters. In addition, the proposed NES-EH can achieve the goal of higher power density and normalized power density under low-amplitude excitation and simultaneously have a good vibration absorption effect. Finally, approximate analytical solutions are obtained by using HBM to exhibit various bifurcations and singularities. • Simply-supported bi-stable piezoelectric composite is first used to integrate vibration absorption and energy harvesting. • NES-EH has advantages of light weight, simple and reliable structure dueto no high strength frame or external device. • Mathematical modeling is developed to forecast the performances of NES-EH. • The effects of excitation amplitude, concentrated mass of NES-EH, geometries of BPCL, and load resistance are considered. [ABSTRACT FROM AUTHOR]

Unlabelled Image In this paper, a novel design concept and manufacturing method for the compliant bistable structure is proposed. The pulsed laser technique is utilized as the manufacturing method for both the fabrication and the introduction of desired pre-stresses, simultaneously. Based on this concept, a novel bistable structure consisted of one pre-compressed main beam, and a pair of supporting beams is designed and fabricated. The deformation difference between the main beam and the supporting beams induced by laser heating residual stress make the main beam to buckle under the constraints of two supporting beams and possess a bistable feature. The bistable structures can be implemented into other devices in the form of cantilevers thanks to the internal integration of the buckled beam and the boundary conditions. The characteristics of this new bistable structure, including its stable shape and snap-through response, are investigated both experimentally and numerically. During the snap forth and back process with the snapping load of 19 mN and the required energy of 77 mN·mm, an impressive energy dissipation with a loss factor value of 0.3 exists. Finally, a parametric study was carried out to find the critical performance parameters. • A novel bistable structure is designed and fabricated successfully by the pulsed laser machining technique. • The bistable structure can be mounted under the cantilever boundary and exhibits strong hysteresis and feature of energy dissipation. • The bistability of the proposed structure can be adjusted by processing parameters and geometry parameters. [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]

In this work, a bistable piezoelectric wind energy harvester (BPEH) is proposed, which is primarily made of bistable hybrid symmetric laminate (BHSL) and PZT, manufactured through a curing process. The air-solid-electric coupled finite element analysis model is established to simulate the dynamic response behavior of the BPEH and investigate the effects of varying airflow velocities on the flow field characteristics and performance output. A series of experimental studies on BPEH were conducted in the wind speed range of 8.5 m/s-16.5 m/s. The results show that at a wind speed of 14.5 m/s, the BPEH has an optimum external load of 60 k Ω , a maximum power output of 7.21 mW and a maximum amplitude of 93.065 mm. Therefore, the simple structure of the harvester proposed in this work may open a new way for bistable composite structures to acquire wind energy widely in natural environments. [Display omitted] [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]

This paper presents a multistable variable cross-section laminate (MVCL), which is designed by applying the displacement constraint at the two opposing ends of the laminate. A theoretical model describing the MVCL as rigid bars connected with compliant hinges is built to predict the equilibrium configurations and snap-through loads of the MVCL. The snap-through process of the multistable structure is investigated via experiment and finite element analysis (FEA). Subsequently, the theoretical model is improved by simplifying the middle segment of the MVCL as an elastic beam. Good agreement is obtained between the experimental test, FEA, and improved theoretical model results. It is shown that the current approach can be successfully applied to predict the equilibrium configurations and snap-through loads of an MVCL. The snap-through loads can be adjusted by changing the middle segment length of an MVCL. [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]

With the 3:1 internal resonance, the primary and secondary resonances of an axially moving thin circular cylindrical panel are investigated in the present work. The governing equation and the compatibility equation are established based on the Donnell's nonlinear shell theory and solved to obtain the nonlinear steady-state responses by combining the Galerkin method and the method of multiple scales. The analytical solutions are verified by numerical solutions based on the Runge-Kutta Method. The governing equation includes both the quadratic nonlinearity and the cubic nonlinearity, so the perturbation solutions need to consider three time scales. The quadratic nonlinearity causes the softening behavior of the system. Natural frequencies and the 3:1 internal resonance condition are obtained by the linear analysis. Under the primary resonance, the internal resonance causes the coupling of the first two modes to complicate the nonlinear dynamic response. The response for the second mode possesses an extra bulge or peak due to the internal resonance. The quadratic nonlinearity results in the zero frequency drift and the second-order harmonic. Under the secondary resonance, the exciting force only arouses the second mode. Results are shown to examine the effects of the internal resonance, the exciting force and viscous damping coefficients on the nonlinear dynamic response of an axially moving thin circular cylindrical panel. • Axially moving circular cylindrical panels is non-linearly modeled. • Both primary and secondary resonances under 3:1 internal resonance are investigated. • Energy transfer among first two modes，zero frequency drift and second-order harmonic is found. [ABSTRACT FROM AUTHOR]

With the development of materials science and technology into the nano-/micro-world, multi-scale problems have become a research focus. Multi-scale calculations usually select a periodic structure as a representative unit with a certain physical meaning and can represent the material properties at a given scale. However, due to the large number of representative elements with complex shape and boundary conditions, the workload of multi-scale calculations is normally huge. In the present effort, a novel virtual scale method is proposed for multi-scale calculations. To demonstrate the validity and significance of the new algorithm, multi-scale calculations have been carried out for the prediction of properties of the ever-popular fiber reinforced composite materials. The equivalent elastic modulus, Poisson's ratio and coefficient of thermal expansion (CTEs) of fiber reinforced plastic in different scales predicted by the new method have been compared with those predicted by the well-established finite element method (FEM) and checked against the experimental results. The good agreements offer solid proof in terms of the validity of the newly developed virtual scale method. In principle, the method can be extended to tackle all multi-scale problems. • The concept of virtual scale for the purpose of multi-scale calculation is proposed. • The thermal residual stress of the composite is calculated. • The workload of multi-scale calculations of composite materials is greatly reduced by introducing virtual algorithm. [ABSTRACT FROM AUTHOR]

The woven composite twisted structure under cantilever load is studied using experimental and multiscale numerical methods. The uncertain geometry parameters inside the twisted specimen are identified using Micro-CT scanning technology, and quantified using multivariate Gaussian random field theory. A high-fidelity meso-Representative Volume Cell (RVC) database after data clustering is established using these uncertainties, in which the warp and weft yarns are no longer regular orthogonality, the yarn cross-sectional area and the yarns gap exhibit variability. The statistical uncertainty quantification and propagation are further integrated into the coupled Finite Element-Fast Fourier Transformation (FE-FFT) concurrent multiscale method to reveal the damage and failure mechanisms of the woven composite twisted structure. The numerical results are in good agreement with the experiment results. This study can be helpful of designing the woven composite blade structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• A baseline-free defect localization method based on the mode conversion and reciprocity principle. • A model function with five parameters to model the conversed wave packets. • Verify the feasibility on aluminum plates via the numerical and experiment methods. Guided wave (GW) plays an important role in nondestructive testing and structural health monitoring. In the general Lamb wave inspection, difference between the baselines and the measured signals are used for structural damage evaluation. However, the baselines are unavoidably influenced by operational and environmental conditions leads to an increased error during inspection. To deal with this issue, this paper presents a base-line free method based on the mode conversion and reciprocity principle of Lamb wave. Once the defect is asymmetrical with respect to the transducer pair (two identical piezoelectric transducers used as actuator and receiver respectively), the elastic wave path length of the converted mode will be different, resulting in failing of the reciprocity principle. By processing the signals received by the transducer pair and extracting the time parameters of the wave packets in mode conversion signals, the defect can be localized. Results from the signals generated by numerical simulation are presented to verify the feasibility of the method, and the effectiveness of the proposed baseline-free method is demonstrated with experimental results. [ABSTRACT FROM AUTHOR]