Acta Mechanica Solida Sinica最新文献

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.

It has been experimentally observed that, in the perforation of metal plates by a flat-nosed projectile, there exists a plateau phenomenon where the ballistic limit increases slightly with increasing plate thickness, which is related to a change in the mode of failure. No theoretical model has so far explained this phenomenon satisfactorily. This paper presents a combined numerical and theoretical study on the perforation of 2024-T351 aluminum plates struck by flat-nosed projectiles. First, numerical simulations are performed to investigate the failure mechanisms/deformation modes of the aluminum plates. Then, a theoretical model is proposed based on the numerical results and the experimental observations within a unified framework. The model takes into account the main energy absorbing mechanisms and the corresponding energies absorbed are determined analytically. In particular, a dimensionless equation is suggested to describe the relationship between global deformations and impact velocity. It transpires that the model predictions are in good agreement with the test data and the numerical results for the perforation of 2024-T351 aluminum plates struck by rigid flat-nosed projectiles in terms of residual velocity, ballistic limit, relationship between global deformations and impact velocity, and transition of failure modes. It also transpires that the present model can predict the “plateau” phenomenon, which shows a slight increase in ballistic limit as plate thickness increases. Furthermore, the energy absorption mechanisms are discussed on the basis of the theoretical analysis.

This paper presents a novel element differential method for modeling cracks in piezoelectric materials, aiming to simulate fracture behaviors and predict the fracture parameter known as the J-integral accurately. The method leverages an efficient collocation technique to satisfy traction and electric charge equilibrium on the crack surface, aligning internal nodes with piezoelectric governing equations without needing integration or variational principles. It combines the strengths of the strong form collocation and finite element methods. The J-integral is derived analytically using the equivalent domain integral method, employing Green's formula and Gauss's divergence theorem to transform line integrals into area integrals for solving two-dimensional piezoelectric material problems. The accuracy of the method is validated through comparison with three typical examples, and it offers fracture prevention strategies for engineering piezoelectric structures under different electrical loading patterns.

Chiral metamaterials are manmade structures with extraordinary mechanical properties derived from their special geometric design instead of chemical composition. To make the mechanical deformation programmable, the non-uniform rational B-spline (NURBS) curves are taken to replace the traditional ligament boundaries of the chiral structure. The Neural networks are innovatively inserted into the calculation of mechanical properties of the chiral structure instead of finite element methods to improve computational efficiency. For the problem of finding structure configuration with specified mechanical properties, such as Young’s modulus, Poisson’s ratio or deformation, an inverse design method using the Neural network-based proxy model is proposed to build the relationship between mechanical properties and geometric configuration. To satisfy some more complex deformation requirements, a non-homogeneous inverse design method is proposed and verified through simulation and experiments. Numerical and test results reveal the high computational efficiency and accuracy of the proposed method in the design of chiral metamaterials.

The measurement field of view of the conventional transmission electron microscopy (TEM) nano-moiré and scanning transmission electron microscopy (STEM) nano-moiré methods is limited to the hundred-nanometer scale, unable to meet the deformation field measurement requirements of micrometer-scale materials such as transistors and micro-devices. This paper proposed a novel measurement method based on scanning secondary moiré, which can realize cross-scale deformation field measurement from nanometers to micrometers and solve the problem of insufficient measurement accuracy when using only the TEM moiré method. This method utilized the electron wave in the TEM passing through the atomic lattice of two layers of different materials to generate TEM moiré. On this basis, the TEM was tuned to the STEM mode, and by adjusting parameters such as the amount of defocusing, magnification, scanning angle, etc., the electron beam was focused on the position near the interface of the two layers of materials, and at the same time, the scanning line was made approximately parallel to the direction of one of the TEM moiré fringes. The scanning secondary moiré patterns were generated when the scanning spacing was close to the TEM moiré spacing. Through this method, the deformation field, mechanical properties, and internal defects of crystals can be detected by a large field of view with high sensitivity and high efficiency. Compared to traditional methods, the advantages of scanning secondary moiré method lie in significantly improving the measurement field of TEM moiré and STEM moiré methods, realizing the cross-scale visualization measurement from nanometers to micrometers, and possessing atomic-level displacement measurement sensitivity. It can also simplify and efficiently identify dislocations, offering a new method for large-area visualization observation of dislocation density in broad application prospects.

Brittle materials, such as silicon, glass, and ceramics, are widely used in engineering via adhesive bonding. The assessment of adhesive strength of brittle materials to other adherends is essential for their applications. Compared with metals and composites, for which standard testing methods have been established, the experimental method for brittle adherends has been much less explored. During the adhesive strength test, the brittleness of these materials makes them prone to failure, rather than the interface. It remains a challenge to measure the adhesive strength of brittle adherends. Here we develop an experimental method to address this issue by using a strap joint specimen with a backing layer. We use a single crystal silicon wafer and two PCB (printed circuit board) strips as adherends to make a strap joint specimen. A steel backing layer is glued to the silicon wafer to prevent the failure of silicon. This method enables the measurement of adhesive strength up to 35 MPa. In contrast, that without backing layer can only measure the adhesive strength below 10 MPa. It is found that the backing layer can reduce the stress in the silicon remarkably, while it has much less effect on the stress in the adhesive layer. We confirm that the backing layer has a negligible effect on the measured adhesive strength but expands the working space greatly. Combining finite element analysis and experiments, we establish the phase diagram for the failure modes. This work provides guidance for the measurement of adhesive strength of brittle materials.

The inflation tests of rubbery membranes have been widely employed as an efficient method to characterize the stress response as biaxial loading states. However, most of the previous theoretical works have employed classic hyperelastic models to analyze the deformation behaviors of inflated membranes. The classic models have been demonstrated to lack the ability to capturing the biaxial deformation of rubbers. To address this issue, we have combined the analytical method and the finite element simulation to investigate the deformation response of soft membranes with different constitutive relationships. For the analytical method, the governing ordinary differential equations have been set up for the boundary value problem of inflation tests and further solved using the shooting method. The analytical results are consistent with those obtained from finite element simulation. The results show that the deformation belongs to the unequal biaxial condition rather than the equi-biaxial state unless a neo-Hookean model is adopted. We also perform a parameter study using the extended eight-chain model, which shows that a change in different parameters affects the mechanical response of inflation tests variously. This work may shed light on the future experimental characterization of soft materials using inflation experiments.

With the advancement of micro- and nano-scale devices and systems, there has been growing interest in understanding material mechanics at small scales. Nanowires, as fundamental one-dimensional building blocks, offer significant advantages for constructing micro/nano-electro-mechanical systems (MEMS/NEMS) and serve as an ideal platform for studying their size-dependent mechanical properties. This paper reviews the development and current state of nanowire mechanical testing over the past decade. The first part introduces the related issues of nanowire mechanical testing. The second section explores several key topics and the latest research progress regarding the mechanical properties of nanowires, including ultralarge elastic strain, large plastic strain, ‘smaller is stronger’, cold welding, and ductile-to-brittle transition. Finally, the paper envisions future development directions, identifying possible research hotspots and application prospects.

This study investigates the nonlinear resonance responses of suspended cables subjected to multi-frequency excitations and time-delayed feedback. Two specific combinations and simultaneous resonances are selected for detailed examination. Initially, utilizing Hamilton’s variational principle, a nonlinear vibration control model of suspended cables under multi-frequency excitations and longitudinal time-delayed velocity feedback is developed, and the Galerkin method is employed to obtain the discrete model. Subsequently, focusing solely on single-mode discretization, analytical solutions for the two simultaneous resonances are derived using the method of multiple scales. The frequency response equations are derived, and the stability analysis is presented for two simultaneous resonance cases. The results demonstrate that suspended cables exhibit complex nonlinearity under multi-frequency excitations. Multiple solutions under multi-frequency excitation can be distinguished through the frequency–response and the detuning-phase curves. By adjusting the control gain and time delay, the resonance range, response amplitude, and phase of suspended cables can be modified.

This research investigates the bending response of folded multi-celled tubes (FMTs) fabricated by folded metal sheets. A three-point bending test for FMTs with circular and square sections is designed and introduced. The base numerical models are correlated with physical experiments and a static crashworthiness analysis of six FMT configurations to assess their energy absorption characteristics. The influences of thickness, sectional shape, and load direction on the bending response are studied. Results indicate that increasing the thickness of the tube and radian of the inner tube enhances the crashworthiness performance of FMT, yielding a 20.50% increase in mean crushing force, a 55.53% increase in specific energy absorption, and an 18.05% decrease in peak crushing force compared to traditional multi-celled tubes (TMTs). A theoretical analysis of the specific energy absorption indicates that FMTs outperform TMTs, particularly when the peak crushing force is prominent. This study highlights the innovative and practical potential of FMTs to improve the crashworthiness of thin-walled structures.