Acta Mechanica Solida Sinica最新文献

The classical two-scale asymptotic paradigm provides macroscopic and microscopic analyses for the elastodynamic homogenization of periodic composites based on the spatial or/and temporal variable, which offers an approximate framework for the asymptotic homogenization analysis of the motion equation. However, in this framework, the growing complexity of the homogenization formulation gradually becomes an obstacle as the asymptotic order increases. In such a context, a compact, fast, and accurate asymptotic paradigm is developed. This work reviews the high-order spatial two-scale asymptotic paradigm with the effective displacement field representation and optimizes the implementation by symmetrizing the tensor to be determined. Remarkably, the modified implementation gets rid of the excessive memory consumption required for computing the high-order tensor, which is demonstrated by representative one- and two-dimensional cases. The numerical results show that (1) the contrast of the material parameters between media in composites directly affects the convergence rate of the asymptotic results for the homogenization of periodic composites, (2) the convergence error of the asymptotic results mainly comes from the truncation error of the modified asymptotic homogenized motion equation, and (3) the excessive norm of the normalized wavenumber vector in the two-dimensional inclusion case may lead to a non-convergence of the asymptotic results.

Designing materials that mitigate impacts effectively are crucial for protecting people and structures. Here, a single-resonator metamaterial with negative mass characteristics is proposed for impact mitigation, and numerical analysis of wave propagation shows explicitly how the spring stiffness and number of unit cells influence that mitigation. The results show clearly that a metamaterial with differing microstructural stiffness is better at mitigating the effect of a shock wave than one with a unique stiffness. Also, there is a critical number of unit cells beyond which the shock wave is not attenuated further, but the fabrication complexity increases. In the 40 groups of microstructural regions in this example, the attenuation effect no longer increases when there are more than 35 groups. This work offers guidance for microstructure designs in metamaterials and provides new ideas for using metamaterials to mitigate shock waves.

Non-uniform deformation of the dielectric subjected to external forces can induce the flexoelectric effect, a phenomenon that couples electrical polarization to strain gradients. However, limited by the size effects, flexoelectricity is not significant at the macroscale and only becomes catchable at the microscale and nanoscale. In recent work, we obtained a considerable flexoelectric-like response by crumpling the dielectric embedded with charges, i.e., the electret, which significantly improved the flexoelectric effect at the macroscale. In this work, we further optimize the macroscopic performance of the flexoelectric response by applying gradient treatment to the electret films. Specifically, we analytically derive the electromechanical coupling of crumpled electret films with gradients of different thicknesses, charge densities, and Young’s moduli as key design variables. It is shown that the gradient-oriented electret film can be tuned to nearly five times that of a uniform electret film.

Single-phase concentrated solid solution alloys (SP-CSAs), including high-entropy alloys, have received extensive attention due to their excellent irradiation resistance. In this work, displacement cascade simulations are conducted using the molecular dynamics method to study the evolution of defects in Ni-based SP-CSAs. Compared with pure Ni, the NiCr, NiCo, and NiCu alloys exhibit a larger number of Frankel pairs (FPs) in the thermal peak stage, but a smaller number of surviving FPs. However, the NiFe alloy displays the opposite phenomenon. To explain these different observations for NiFe and other alloys, the formation energy and migration energy of interstitials/vacancies are calculated. In the NiFe alloy, both the formation energy and migration energy barrier are higher. On the other hand, in NiCr and other alloys, the formation energy of interstitials/vacancies is lower, as is the migration energy barrier of interstitials. The energy analysis agrees well with previous observations. The present work provides new insights into the mechanism behind the irradiation resistance of binary Ni-based SP-CSAs.

In this paper, the method of polynomial particular solutions is used to solve nonlinear Poisson-type partial differential equations in one, two, and three dimensions. The condition number of the coefficient matrix is reduced through the implementation of multiple scale technique, ultimately yielding a stable numerical solution. The methodological process can be divided into two main parts: first, identifying the corresponding polynomial particular solutions for the linear differential operator terms in the governing equations, and second, employing these polynomial particular solutions as basis function to iteratively solve the remaining nonlinear terms within the governing equations. Additionally, we investigate the potential improvement in numerical accuracy for equations with singularities in the analytical solution by shifting the computational domain a certain distance. Numerical experiments are conducted to assess both the accuracy and stability of the proposed method. A comparison of the obtained results with those produced by other numerical methods demonstrates the accuracy, stability, and efficiency of the proposed method in handling nonlinear Poisson-type partial differential equations.

Tailoring grain size can improve the strength of polycrystals by regulating the proportion of grains to grain boundaries and the interaction area. As the grain size decreases to the nanoscale, the deformation mechanism in polycrystals shifts from being primarily mediated by dislocations to deformation occurring within the grains and grain boundaries. However, the mechanism responsible for fine-grain strengthening in ferroelectric materials remains unclear, primarily due to the complex multi-field coupling effect arising from spontaneous polarization. Through molecular dynamics simulations, we investigate the strengthening mechanism of barium titanate (BaTiO₃), with extremely fine-grain sizes. This material exhibits an inverse Hall–Petch relationship between grain size and strength, rooting in the inhomogeneous concentration of atomic strain and grain rotation. Furthermore, we present a theoretical model to predict the transition from the inverse Hall–Petch stage to the Hall–Petch stage based on strength variations with size, which aligns well with the simulation results. It has been found that the piezoelectric properties of the BaTiO₃ are affected by polarization domain switching at various grain sizes. This study enhances our understanding of the atomic-scale mechanisms that contribute to the performance evolution of fine-grain nano-ferroelectric materials. It also provides valuable insights into the design of extremely small-scale ferroelectric components.

Most existing treatments for origami-folding simulations have focused on regular-shaped configurations. This article aims to introduce a general strategy for simulating and analyzing the deformation process of irregular shapes by means of computational capabilities nowadays. To better simulate origami deformation with folding orders, the concept of plane follow-up is introduced to achieve automated computer simulation of complex folding patterns, thereby avoiding intersection and penetration between planes. Based on the evaluation criteria such as the lowest storage energy with tightening and the fastest pace from tightening to unfolding, the optimal crease distribution patterns for four irregular (‘N’-, ‘T’-, ‘O’-, and ‘P’-shaped) origami configurations are then presented under five candidates. When the dimensions of the origami are fixed, it is discovered that simpler folding patterns lead to faster deformation of the origami configuration. When the folding complexity is fixed, higher strain energy results in more rapid origami expansion.

Piezoelectric semiconductors (PSs), such as ZnO and GaN, known as the third-generation semiconductors, have promising applications in electronic and optoelectronic devices due to the coexistence and interaction of piezoelectricity and semiconductor properties. Theoretical modeling of PS structures under external loads, such as thermal and mechanical loads, plays a crucial role in the design of PS devices. In this work, we propose a nonlinear fully coupling theoretical model and investigate the multi-field coupling behaviors of PS structures and PN junctions under thermal and mechanical loads, considering physical and geometric nonlinearities. The electromechanical and semiconducting behaviors of a PS rod-like structure with flexural deformations under different combinations of temperature changes and mechanical loads are evaluated. The tuning effect of temperature changes and mechanical loads on multi-field coupling behaviors of PSs is revealed. The current–voltage characteristics of PS PN junctions are studied under different combinations of temperature changes and mechanical loads. The obtained results are helpful for the development of novel PS devices.

To reduce the damage of the pressurizing panel structure of a fuselage caused by an explosion at the “least risk bomb location” in an aircraft structure, a new pre-separation panel structure was designed to resist blast loading. First, the dynamic strain response and morphology of impact damage of the new pre-separation panel were measured in an impact damage test. Second, the commercial software LS-DYNA was used to calculate the propagation of the blast shock wave, and the results were compared with empirical equations to verify the rationality of the numerical calculation method. Finally, the fluid–structure coupling method was used to calculate the damage process of the pre-separation panel structure under the impact of an explosion wave and an impact block. The calculated results were in good agreement with the test results, which showed the rationality of the calculation method and the model. The residual strength of the damaged pre-separation panel was significantly higher than that of the original damaged panel. The results show that the new pre-separation panel structure is reasonable and has certain significance for guiding the design of plenum chambers with strong resistance to implosion for aircraft fuselages.

Auxetic metamaterials, which exhibit the negative Poisson’s ratio (NPR) effect, have found wide applications in many engineering fields. However, their high porosity inevitably weakens their bearing capacity and impact resistance. To improve the energy absorption efficiency of auxetic honeycombs, a novel vertex-based hierarchical star-shaped honeycomb (VSH) is designed by replacing each vertex in the classical star-shaped honeycomb (SSH) with a newly added self-similar sub-cell. An analytical model is built to investigate the Young’s modulus of VSH, which shows good agreement with experimental results and numerical simulations. The in-plane dynamic crushing behaviors of VSH at three different crushing velocities are investigated, and empirical formulas for the densification strain and plateau stress are deduced. Numerical results reveal more stable deformation modes for VSH, attributed to the addition of self-similar star-shaped sub-cells. Moreover, compared with SSH under the same relative densities, VSH exhibits better specific energy absorption and higher plateau stresses. Therefore, VSH is verified to be a better candidate for energy absorption while maintaining the auxetic effect. This study is expected to provide a new design strategy for auxetic honeycombs.