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Dielectric elastomers (DE), renowned for their lightweight, rapid response, high energy density, and efficient conversion, have garnered significant attention in the realm of avian flight bionics. However, a lack of understanding of the mechanical principles underlying flapping wing biomimetics has hindered accurate simulations of actual bird flight postures. To address this, a stiffness-variable DE-based wing (DEW) has been designed, inspired by the characteristics of seagulls, to mimic the wing deformations across different bird flight phases. The evolution of the DEW’s deformation is modeled based on the differential equation describing the bending curve of a DE cantilever beam. By applying different voltage cycles, three continuous avian flight postures have been replicated: takeoff, cruising, and hovering. The simulation results demonstrate that the stiffness-variable DEW effectively mimics the wing deformations observed in birds during different flight postures, closely resembling real-world flight conditions. This study has the potential to serve as an important reference for exploring changes in bird flight behavior, thereby advancing the application of DE materials in the field of soft robotics. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators (DEAs) are increasingly recognized as pivotal components in flexible robotic actuators due to their substantial displacement, high energy density, rapid response times, and adaptable design characteristics. Nonetheless, the widespread adoption of DEAs is impeded by challenges such as elevated manufacturing costs and inherent nonlinear characteristics, which obscure a comprehensive understanding of the interplay between dielectric elastomer (DE) related material properties and voltage stimuli governing DEA operation. This study introduces a sophisticated finite element model that integrates Maxwell stress principles with the hyperelastic behavior inherent in DEs, enabling the numerical elucidation of DEA gripper dynamics. Utilizing this model, the minimum energy structure of DEs and their nonlinear actuation behavior under diverse electric field conditions are analyzed. The model's efficacy is validated through a meticulous comparison of simulated angular deflection and displacement with experimental results obtained from a six-segment DEA gripper across varying electric field intensities. Additionally, the impact of dielectric coefficients on the electro-actuated deformation of the DEA gripper is rigorously assessed, revealing a noteworthy enhancement in electro-actuation efficiency with increasing dielectric constants, particularly under high electric field conditions. Furthermore, the deformation differences of multi-segment DEA grippers under different voltage control strategies were investigated. The causes of these differences are discussed through stress analysis, and a sequential voltage application strategy is designed to optimize the gripping effect. The insights gleaned from this study offer valuable guidance for the design and optimization of DEAs tailored to diverse deformation requirements within the field of flexible robotic actuators. [ABSTRACT FROM AUTHOR]

Sodium (Na) dendrite growth poses challenges such as short circuits and capacity loss, and the underlying mechanisms are unclear. Although the experiments of Na dendrite growth were reported, there are very few simulations that can assist in analyzing its morphology evolution mechanism. In addressing this challenge, we develop a phase-field model to explore the influence of current density, anisotropic strength, and Na-ion consumption on the evolution of Na dendrite morphology. It is found that higher current density promotes more dendrite growth and lateral branches. Anisotropy strength influences dendrite growth rates horizontally and vertically, with horizontal growth exceeding or equaling vertical growth, reducing short-circuit risks. Increased Na-ion consumption results in significant lateral branches, kinks, and pores in dendrite structures. These results offer valuable insights into mitigating the formation of erratic dendrites, holding significant implications for the advancement of Na-based batteries with high stability and safety. [Display omitted] • Revealing Na dendrite dynamics intricacies via a novel phase field model. • Exploring effects of multi-factor on Na dendrite morphology evolution. • Mitigating short-circuit risks by controlling dendrite growth dynamics. [ABSTRACT FROM AUTHOR]

• A multi-physics and multi-scale framework for electrochemo-mechanical behavior of ASSBs was established. • The role of gradient plasticity in the governing equation for multiple physical fields was discussed. • An upscaling homogenization procedure was proposed to boost efficiency of buckling analysis. All-solid-state batteries (ASSBs) are high-energy, high-power batteries. To enhance the understanding of the electrochemical-mechanical behavior in ASSBs across different scales, we developed a multi-physics and multi-scale modeling framework. This framework incorporates elastoplastic finite deformation and electrode microstructures of ASSBs, and the role of gradient plasticity in the governing equation for multiple physical fields was discussed. Utilizing X-ray computed tomography, we reconstructed the microstructure through a machine learning (ML)-informed image segmentation process. Our study clarifies the impact of electrode microstructures on concentration, stress, voltage, delamination and buckling from AM to electrode scale. Comparative analysis of the Feret diameter distribution of active materials (AMs) shows that ML-informed image segmentation outperforms two traditional segmentation methods. We observed that the asynchronous diffusion saturation of AMs, varying in shape and size, significantly influences the electrochemical-mechanical behavior of ASSBs, resulting in complicated debonding indices and J-integral distribution at the interface. The proposed upscaling homogenization procedure is demonstrated to be efficient for buckling analysis, with the shape mode closely matching existing experimental observations. These results shed light on the critical multi-physics and multi-scale coupling mechanisms in ASSBs. [ABSTRACT FROM AUTHOR]

The optimization of traction-separation parameters within the cohesive zone model (CZM) is crucial for accurately simulating electrode peeling failure in lithium-ion batteries. This study performed 180° peeling tests on NCM electrodes and used Abaqus software alongside the sim-flow optimization tool for simulation analysis, aiming to accurately replicate the failure behavior at the lithium-ion battery electrode interface. Experimental results were used to determine the fracture energy of the electrode interface, while numerical simulations analyzed the peeling performance of the electrode. By fitting the force-displacement curves from both simulation and experiment, the traction-separation parameters within the bilinear CZM were optimized. Additionally, the study analyzed the effects of traction-separation parameters, as well as the modulus and thickness of the current collector, on peeling behavior. The results showed that a significant increase in the interface stiffness and strength increased the steady-state peeling force. Among these, the fracture energy had the most significant influence on the steady-state peeling force. Furthermore, while the modulus and thickness of the current collector affected the maximum peeling force, their effect on the steady-state peeling force was negligible. These findings enhance the accuracy of simulating the failure behavior of the electrode interface. [Display omitted] [ABSTRACT FROM AUTHOR]

A general model was developed to predict the temperature-dependent modulus and yield strength of different thermoplastic polymers. This model, which depends on only two parameters with clear and specific physical meanings, can describe the temperature-dependent modulus and yield strength of thermoplastic polymers over the full glass transition region. The temperature-dependent modulus and yield strength of three thermoplastic polymers were measured by uniaxial tension tests over a temperature range of 243–383 K. The predictions showed excellent agreement with the experimental data. Sensitivity analysis of model input parameters showed negligible effect on the present general model. The universality of the present general model was further validated, showing excellent agreement with published experimental data on other thermoplastic polymers and their composites. [ABSTRACT FROM AUTHOR]

The effects of hydrostatic pressure and modulus softening on electrode curvature and stress in a bilayer electrode plate are studied. It is found the hydrostatic pressure facilitates Li-ion diffusion. Modulus softening can weaken the stress assisted diffusion, promote the electrode to bend and reduce the stress. The electrode would nearly reach a lock-up state of deformation in the late charging process for potentiostatic charging, but the electrode bends continuously for galvanostatic charging. It is also found the electrode curvature firstly increases, and then reduces as current collector thickness increases, but decreases continuously by increasing the modulus of current collector. The thicker current collector and higher rigidity of current collector can block Li-ion diffusion for potentiostatic charging. Finally, the optimized charging procedure for reducing the bending deformation is galvanostatic first followed by potentiostatic, the current collector should be as thin and soft as possible when its own strength and role are satisfied. [ABSTRACT FROM AUTHOR]

Temperature-dependent modulus of glass fiber/epoxy composite laminates was studied at temperatures ranging from room temperature up to 120℃. The storage modulus, loss modulus, loss factor, and glass transition temperature of two layer-up composite laminates were investigated by dynamic mechanic analysis. Static flexural modulus was also measured by control force mode in dynamic mechanic analysis. A new and simple temperature-dependent model both for the dynamic storage modulus and static flexural modulus was developed. This model depends only on one parameter which has specific physical meaning. The model prediction showed excellent agreement with our own experimental results over the full range of transition region. Furthermore, comparing our model’s prediction and other experimental data of many types of composites, which were studied by other researchers, we point to the fact that our model can be applied to many different polymer matrix composites. [ABSTRACT FROM AUTHOR]

Abstract: The fiber Bragg grating (FBG) sensors have been well studied and used to monitor strain, temperature, or damage in engineering structures which were serviced at ambient temperatures. In order to monitor structure responses which were operated at cryogenic environments, the strain and temperature performance of fiber Bragg grating (FBG) sensors were studied in the temperature range of 123–273K by three FBG experiments. The temperature sensitive coefficient, strain sensitive coefficient and cross-sensitivity coefficient were derived analytically and verified by experiments. The relationship between the wavelength shift and temperature could be characterized by three-order polynomial. The wavelength shift was linear with the longitudinal strain. Cross sensitivity increased with lower temperature. [Copyright &y& Elsevier]

The cure characterization of a new BMI resin was investigated to ascertain a suitable cure model for the material. A series of isothermal differential scanning calorimetry (DSC) runs from 170°C to 220°C provided information about the cure characterization. All “kinetic triplet” (i. e., Arrhenius parameters A, activation energy E, and the reaction model, f (α)) of this new BMI system were calculated. It was found that the cure characterization of this new BMI could be expressed by n th‐order cure reaction. [ABSTRACT FROM AUTHOR]

Abstract: The development of temperature field of thick thermoset matrix laminates manufactured by autoclave vacuum bag process were measured and compared with the numerically calculated results. The finite element formulation of the transient heat transfer problem was carried out for polymeric matrix composite materials from the heat transfer differential equations including internal heat generation produced by exothermic chemical reactions. The finite element analysis software, which was based on the general finite element software package, was developed for numerical simulation of the entire composite process. From the experimental and numerical results, it was found that the measured temperatures profiles were in good agreement with the numerical ones, and conventional cure cycles recommended by prepreg manufacturers for thin laminates should be modified to reduce out-of-plane temperature gradient. [Copyright &y& Elsevier]

[Display omitted] Diffusion-induced stress (DIS) generation in the microstructure and contact loss at the active material (AM)/solid electrolyte (SE) and active layer/current collector interfaces strongly affect the electrochemical and mechanical stabilities of all-solid-state batteries (ASSBs). A fully coupled chemo-mechanical model based on the 3D microstructure of ASSBs reconstructed via synchrotron transmission X-ray microscopy tomography was established to analyze the voltage profile of different Young's modulus matching factors for AM and SE, singular DIS generation, and interfacial failure in ASSBs. The working voltage plateau of the ASSBs increases with the Young's modulus of the SE, while the voltage oscillation at the beginning of the delithiation process was attributed to the chemical potential difference between the various points of the active particles. Stress and deformation are key factors affecting the interfacial stability of ASSBs. A singular stress field, in which strain localization preferentially occurs in AM particles, results in complex interfacial failures in ASSBs. Theoretical considerations suggest that an interlayer combining high interfacial toughness with a sufficient electron transport coefficient will prevent the delamination of ASSBs by making strain localization away from the current collector. The established model explains the electrochemo-mechanical behavior in response to different mechanical properties of AM and SE and the interfacial failure mechanism of ASSBs, which in turn will offer guidance in the design of future ASSBs. [ABSTRACT FROM AUTHOR]

The microstructure of electrodes is intrinsically complex and thus should be determined prior to the analysis of the chemo-mechanical performance during charge/discharge cycles. In this study, a microstructurally resolved, fully coupled chemo-mechanical model was developed to investigate the structure–property relationship of electrodes in the framework of elastoplastic finite deformation. The active particles, binder, and pores of real electrode images were segmented and reconstructed using the region-growing method. The effects of the electrode microstructure on the diffusion-induced stress (DIS) distribution, local electric potential and electrical resistance, interaction between the binder and particles, and mechanical failure of the particle–binder interface (PBI) were elucidated considering the finite concentration effect, concentration-dependent modulus and yield strength. The results indicate that the microstructure of electrodes significantly influences the distribution of DIS, local electric potential, and electrical resistance. The elastoplastic finite deformation theory can accurately describe the stress singularities that occur near sharply concave regions. Additionally, the use of a relatively soft binder was found to accommodate the expansion of active particles and mitigate the effects of particle interaction. Furthermore, being able to ensure that the active particles maintain a simple convex shape can reduce the likelihood of particle pulverization and PBI debonding. These results will enhance the understanding of the evolution of stress generation, the local electric potential and electrical resistance, and the mechanical failure of the PBI within the microstructure of porous electrodes; the results also emphasize the need for an optimized microstructure design for porous electrodes. [ABSTRACT FROM AUTHOR]

Progressive delamination driven by Li-ion diffusion in elastic disk-like thin film electrodes of Li-ion batteries is modeled based on the cohesive model. Axisymmetric diffusion model is considered under both galvanostatic and potentiostatic operations. The effect of edge diffusion on the delamination process is evaluated. It is found that the diffusion from edge leads to an earlier delamination initiation. The edge effect is significant for active disks with a small aspect ratio, but negligible for the case of large aspect ratio. The edge diffusion is weaker in the potentiostatic operation than in the galvanostatic operation. [ABSTRACT FROM AUTHOR]

In-plane compressive strength of z-pinned unidirectional composites is predicted by using variational principle and maximum shear strength criterion. The fiber waviness and the fiber volume content concentration, which are inhomogeneously distributed, as well as the resin-rich pocket, are taken into account. The predicted results are in good agreement with the test data. The effects of pin parameters on the compressive strength of z-pinned laminates are discussed in detail. The results showed that in-plane compressive strength of laminates decreases as the diameter of pin increases under the same pin volume content. Compressive strength decreases as the pin volume content increases under the same pin diameter. The non-linear shear property of matrix has relatively remarkable influence on compressive strength of unidirectional z-pinned laminates when pin diameter is small. [ABSTRACT FROM AUTHOR]

Thick electrodes whose active materials have high areal density may improve the energy densities of lithium-ion batteries. However, the weakened rate abilities and cycle lifetimes of such electrodes significantly limit their practical applications. In this study, a modified two-dimensional model was built to evaluate the influence of the electrode structure on the lithiation process. Gradient electrodes with different particle sizes along the thickness direction are designed and fabricated via a two-layer coating process. The gradient design in the thickness direction is confirmed by three-dimensional digital microscopy, energy-dispersive spectroscopy, X-ray diffraction, and scanning electron microscopy. Galvanostatic charge/discharge cycling tests and electrochemical impedance spectroscopy are performed to investigate the electrochemical properties of the fabricated gradient electrodes. The simulation results indicate that the gradient electrode structure can enhance the utilization of electrode particles on the current collector side and alleviate the nonuniformity of the solid-phase Li concentration along the thickness direction. High electrochemical performance and long-term cycling stability of the designed gradient electrodes are verified by electrochemical test. The gradient structure fabricated via multi-layer coating processes can be used to improve the electrochemical performance of thick electrodes. [ABSTRACT FROM AUTHOR]

• An analytical model was established to characterize the mode-II energy release rate. • A novel plasticity-assisted zero-degree peeling test was proposed to obtain a stable crack propagation stage. • The effect of dimensionless stress, indices of hardening, and load transfer length on energy release rate were analyzed. • An excellent agreement between the theoretical calculation and numerical result was demonstrated. Lithium-ion batteries integrate heterogeneous materials such as active layers and current collectors, resulting in interfaces prone to delamination during the charge/discharge process. The mode-II energy release rate is a key index to evaluate the interfacial adhesion properties and structural integrity of electrodes. In this study, an analytical model considering the energy balance principle and a nonlinear constitutive model was established to characterize the mode-II energy release rate. A novel plasticity-assisted zero-degree peeling test (PAZDPT) is proposed to obtain a stable crack propagation stage where the peeling force is determined to calculate the mode-II energy release rate. Several parameter studies were conducted to verify the approximation of the stress distributions and simplification of the analytical model. The accuracy of the analytical model was validated against finite-element calculations. The results demonstrated an excellent agreement between the theoretical calculation and numerical results. Moreover, PAZDPT is conducive to steady crack propagation because it restricts the energy accumulation around the crack tip. The analytical model and newly proposed PAZDPT can also be extended to determine the mode-II energy release rate of other types of interfaces in bilayer thin-film materials. [ABSTRACT FROM AUTHOR]