Acta Mechanica Solida Sinica最新文献

Attributing to the noteworthy volume change of silicon active particles upon cycling, the porosity of the coated silicon composite electrode can vary significantly and therefore be expected to affect the apparent mechanical response of the composite electrode. However, direct experimental evidence is still lacking. By stripping the active layer from the current collector and performing quasi-static stretching tests, this work shows a direct correlation between the variation of tensile properties and related coating porosity of the silicon composite electrode during lithiation. Although silicon particles soften when lithiated, it is found that the increased particle volume can significantly lower the porosity of the coating, resulting in the densification of the silicon composite electrode and thus reducing the toughness of the silicon composite electrode and making the electrode more prone to lose its mechanical integrity under small strain in service. Based on finite element simulation and experimental data analysis, analytical expressions of equivalent modulus and strength of the porous silicon composite electrode were also constructed and are in good agreement with the experimental values. Moreover, the maximum tensile stress of the electrode was found to be amplified by at least 1.8 times when the coating-dependent porosity is considered, indicating the necessity in the design of electrode structural integrity and optimization in service. The results of work are expected to provide important experimental data and model basis for the mechanical design of silicon composite electrodes upon usage.

The insertion and extraction of lithium ions in active materials lead to significant volumetric deformation, resulting in stresses that drive the mechanical degradation of these materials. This accumulation of mechanical degradation ultimately leads to mechanical failure in lithium-ion batteries (LIB). This paper summarizes the experimental characterization techniques used to observe the mechanical degradation of lithium battery cells, electrodes, and particles across macro, micro, and nano scales. Additionally, the mechanical failure model for LIB that spans from the microscopic to the macroscopic scale has been outlined. Finally, we analyze the current challenges and opportunities, including the standardization of battery measurements, the quantification of mechanical failures, and the correlation between mechanical failures and electrochemical performance.

The advancement of electron microscopy technology has driven the development of electron microscopes that can apply mechanical loading while observing samples, providing a valuable tool for In-Situ mechanical characterization of materials. In response to the need to characterize the evolution of the mechanical behavior of structural materials, such as aerospace materials, in real cryogenic service environments, and to provide an experimental basis for improving their macroscopic cryogenic mechanical properties, the advancement of In-Situ characterization techniques capable of offering both cryogenic environments and mechanical loading has become imperative. There have been scholars using this technique to carry out cryogenic mechanical In-Situ studies of related materials, with experimental studies dominating in general, and a few reviews of mechanical characterization techniques mentioning cryogenic temperatures. In order to make it easier to conduct research using such characterization techniques and to further promote the development of related characterization techniques, this review compiles the previous work and summarizes the electron microscope-based In-Situ characterization techniques for cryogenic micro- and nanomechanics. These techniques primarily include transmission electron microscopy-based cryogenic tensile and indentation methods, as well as scanning electron microscopy-based cryogenic tensile, indentation, compression, and bending methods. Furthermore, the review outlines the prospective future development of In-Situ characterization techniques for cryogenic micro- and nanomechanics.

Natural biomaterials with staggered structures exhibit remarkable mechanical properties owing to their unique microstructure. The microstructural arrangement can induce size-dependent and viscoelastic responses within the material. This study proposes a strain gradient viscoelastic shear-lag model to elucidate the intricate interplay between the strain gradient and viscoelastic effect in staggered shells. Our model clarifies the role of both effects, as experimentally observed, in governing the mechanical properties of these biomaterials. A detailed characterization of the size-dependent responses is conducted through the utilization of a microstructural characterization parameter alongside viscoelastic constitutive models. Then, the effective modulus of the staggered shell is defined and its formula is derived through the Laplace transform. Compared to classical models and even the strain gradient elastic model, the strain gradient viscoelastic model offers calculated moduli that are more consistent with experimental data. Moreover, the strengthening-softening effect of staggered structures is predicted using the strain gradient viscoelastic model and critical energy principle. This study contributes significantly to our understanding of the mechanical behavior of structural materials. Additionally, it provides insights for the design of advanced bionic materials with tailored properties.

Kirigami, through introducing cuts into a thin sheet, can greatly improve the stretchability of structures and also generate complex patterns, showing potentials in various applications. Interestingly, even with the same cutting pattern, the mechanical response of kirigami metamaterials can exhibit significant differences depending on the cutting angles in respect to the loading direction. In this work, we investigate the structural deformation of kirigami metamaterials with square domains and varied cutting angles of 0° and 45°. We further introduce a second level of cutting on the basis of the first cutting pattern. By combining experiments and finite element simulations, it is found that, compared to the commonly used 0° cuts, the two-level kirigami metamaterials with 45° cuts exhibit a unique alternating arrangement phenomenon of expanded/unexpanded states in the loading process, which also results in distinct stress–strain response. Through tuning the cutting patterns of metamaterials with 45° cuts, precise control of the rotation of the kirigami unit is realized, leading to kirigami metamaterials with encryption properties. The current work demonstrates the programmability of structural deformation in hierarchical kirigami metamaterials through controlling the local cutting modes.

Determining the optimal ceramic content of the ceramics-in-polymer composite electrolytes and the appropriate stack pressure can effectively improve the interfacial contact of solid-state batteries (SSBs). Based on the contact mechanics model and constructed by the conjugate gradient method, continuous convolution, and fast Fourier transform, this paper analyzes and compares the interfacial contact responses involving the polymers commonly used in SSBs, which provides the original training data for machine learning. A support vector regression model is established to predict the relationship between the content of ceramics and the interfacial resistance. The Bayesian optimization and K-fold cross-validation are introduced to find the optimal combination of hyperparameters, which accelerates the training process and improves the model’s accuracy. We found the relationship between the content of ceramics, the stack pressure, and the interfacial resistance. The results can be taken as a reference for the design of the low-resistance composite electrolytes for solid-state batteries.

This study investigates the nonlinear dynamic properties of rotating functionally graded sandwich rectangular plates in a thermal environment. The nonlinear vibration equations for a rotating metal-ceramic functionally graded sandwich rectangular plate in a thermal environment are derived using classical thin plate theory and Hamilton’s principle, considering geometric nonlinearity, temperature-dependent material properties, and power law distribution of components through the thickness. With cantilever boundary conditions, the flexural nonlinear differential equations of the rectangular sandwich plate are obtained via the Galerkin method. Since the natural vibration differential equations exhibit nonlinear characteristics, the multiscale method is employed to derive the expression for nonlinear natural frequency. An example analysis reveals how the natural frequency of a functionally graded sandwich rectangular plate varies with rotational speed and temperature. Results show that the nonlinear/linear frequency ratio increases with rotational angular velocity Ω and thickness-to-length ratio h/a, follows a cosine-like periodic pattern with the setting angle, and shows a sharp decrease followed by a rapid increase with increasing width-to-length ratio b/a. The derived analytical solutions for nonlinear frequency provide valuable insights for assessing the dynamic characteristics of functionally graded structures.

Layered materials, such as graphite and molybdenum disulfide, are promising for electrode materials and microelectronic devices due to their excellent ion-intercalating properties. However, the intercalation and de-intercalation of ions, causing structural deformation and material property variations, would affect battery performance and alter external field responses. The complex problem coupling multiphysics is significant for study and poses a crucial research challenge. This paper reviews the coupling between mechanics, electrochemistry, and electrics during the reaction process, including in situ experimental characterization, theoretical modeling, and design considerations at various scales. Current research has focused on experimental observations beyond the nanoscale and continuum phenomenological models. Further advancements in characterizing layered structural evolution, electron cloud interactions at the atomic level, and developing physics-based multi-field models are essential.

High-entropy alloys (HEAs) exhibit the excellent elevated-temperature performance and irradiation resistance due to the important core effect of serious lattice distortion for impeding dislocation motion, as candidate materials for nuclear applications. Despite the growth of the nuclear power sector, the effects of high-temperature and high-dose irradiation-induced voids on the mechanical properties of HEA in higher power nuclear reactors remain insufficiently researched, hindering its industrial application. In this study, we establish a consistent parameterization crystal plastic constitutive model for the hardening and creep behaviors of HEA, incorporating the spatial distribution of void size and shape effects, in contrast to traditional creep models that rely on temperature-related fitting parameters of the phenomenological power law equation. The model matches well with experimental data at different temperatures and irradiation doses, demonstrating its robustness. The effects of irradiation dose, temperature, and degree of lattice distortion on irradiation hardening and creep behavior of void-containing HEA are investigated. The results indicate that HEA with high lattice distortion exhibits better creep resistance under higher stress loads. The yield stress of irradiated HEA increases with increasing irradiation dose and temperature. The creep resistance increases with increasing irradiation dose and decreases with increasing irradiation temperature. The increase in irradiation dose causes a specific morphological transformation from spherical to cubic voids. The modeling and results could provide an effective theoretical way for tuning the yield strength and alloy design in advanced HEAs to meet irradiation properties.

The potentiostatic intermittent titration technique (PITT) is widely used to determine the diffusion coefficient of ions in electrode materials for rechargeable batteries such as lithium-ion or sodium-ion batteries, predicated on the assumption that the insertion/extraction of ions in the host materials is governed by diffusion. However, in practical scenarios, the electrochemical process might be dominated by interfacial reaction kinetics rather than diffusion. The present work derives analytical equations for electric current by considering the finite interfacial reaction kinetics and small overpotentials during PITT measurements and further studies the chemical stress field induced by the interfacial reaction-controlled ion insertion. The exchange current density (({j}_{0})) can be ascertained using the analytical equation, which dictates the magnitude and decay rate of the electric current during a PITT process. The electric current decays more rapidly, and consequently, the lithium concentration reaches equilibrium faster for larger values of ({j}_{0}). The magnitude of the chemical stress is independent of ({j}_{0}) but depends on the overpotential.