Acta Mechanica Solida Sinica最新文献

Microcracks are common in compact bone, but their continued propagation can lead to macroscopic fractures. These microcracks cannot be visualized radiographically, necessitating alternative noninvasive methods to identify excessive microcracking and prevent fractures. In this study, terahertz time-domain spectroscopy (THz-TDS) was used to examine bone interiors near cracks resulting from loading in bovine tibia samples. Various loading configurations, such as impact, quasi-static loading, and fatigue loading, known to induce different types of micro-scale damage, were applied. The values of refractive index and absorption coefficient of the bone samples were then determined from the THz-TDS spectra acquired before loading and after fracture. The study revealed that different loading configurations led to varying terahertz optical coefficients associated with various types of bone fractures. Specifically, the refractive index notably increased under fatigue loading but remained relatively stable during quasi-static bending. The absorption coefficient of bone decreased only under fatigue loading. Furthermore, samples were subjected to axial and radial impacts without sustaining damage. Results indicated that in the undamaged state, the change in refractive index was smaller compared to after impact failure, while the change in absorption coefficient remained consistent after failure. Under radial impact loading, changes in refractive index and absorption coefficient were significantly more pronounced than under axial loading. Prior to loading, the measured value of refractive index was 2.72 ± 0.11, and the absorption coefficient was 6.33 ± 0.09 mm⁻¹ at 0.5 THz.

Elasto-capillarity phenomena are prevalent in various industrial fields such as mechanical engineering, material science, aerospace, soft robotics, and biomedicine. In this study, two typical peeling processes of slender beams driven by the parallel magnetic field are investigated based on experimental and theoretical analysis. The first is the adhesion of two parallel beams, and the second is the self-folding of a long beam. In these two cases, the energy variation method on the elastica is used, and then, the governing equations and transversality boundary conditions are derived. It is shown that the analytical solutions are in excellent agreement with the experimental data. The effects of magnetic induction intensity, distance, and surface tension on the deflection curve and peeling length of the elastica are fully discussed. The results are instrumental in accurately regulating elasto-capillarity in structures and provide insights for the engineering design of programmable microstructures on surfaces, microsensors, and bionic robots.

Adhesion plays an important role in miniaturized devices and technologies, which depends not only on indentation depth but also on the history of contact making and breaking, giving rise to adhesion hysteresis. In the present work, adhesion hysteresis has been investigated via molecular dynamics simulations on approaching and retracting a rigid tip to and from a substrate. The results show that hysteresis in the force–displacement curve that depends on approaching and retraction velocities arises under both elastic and plastic deformation. The underlying mechanisms have been analyzed. The implications of the results in friction have been discussed briefly.

In this paper, a transversely isotropic piezoelectric half-space with the isotropy axis parallel to the z-axis is considered under rotation on a rigid circular disk bonded to the surface of the piezoelectric medium. This is a type of Reissner–Sagoci mixed boundary value problem. By utilizing the Hankel transform, the mixed boundary value problem is simplified into solving a pair of dual integral equations. Full-field analytical expressions for displacement, stresses, and electric displacement inside the half-space are obtained. The shear stresses and electric displacement on the surface are found to be singular at the edge of the rigid circular disk, and the stress intensity factors and electric displacement intensity factor are defined. Numerical results show that material properties and geometric size have significant effects on displacement, shear stresses, and electric displacement.

Within the context of Gurtin–Murdoch surface elasticity theory, closed-form analytical solutions are derived for an isotropic elastic half-plane subjected to a concentrated/uniform surface load. Both the effects of residual surface stress and surface elasticity are included. Airy stress function method and Fourier integral transform technique are used. The solutions are provided in a compact manner that can easily reduce to special situations that take into account either one surface effect or none at all. Numerical results indicate that surface effects generally lower the stress levels and smooth the deformation profiles in the half-plane. Surface elasticity plays a dominant role in the in-plane elastic fields for a tangentially loaded half-plane, while the effect of residual surface stress is fundamentally crucial for the out-of-plane stress and displacement when the half-plane is normally loaded. In the remaining situations, combined effects of surface elasticity and residual surface stress should be considered. The results for a concentrated surface force serve essentially as fundamental solutions of the Flamant and the half-plane Cerruti problems with surface effects. The solutions presented in this work may be helpful for understanding the contact behaviors between solids at the nanoscale.

This paper presents isogeometric analysis (IGA)-based topology optimization for electrical performance of three-dimensional (3D) flexoelectric structures. IGA is employed to provide ({C}^{1}) continuity in shape function, which is required in treating high-order electromechanical coupling equations. To improve the computational efficiency in treating 3D problems, the redundant degrees of freedom removal technique is introduced. Regularization treatments are also implemented to avoid the numerical singularity induced by flexoelectricity. Both virtual loads and strain energy constraints are taken into consideration to prevent unexpected structural disconnection. Numerical examples and experiments on optimized structures demonstrate that the flexoelectric performance can be effectively improved using the proposed approach.

Based on the three-dimensional (3D) basic equations of piezoelectric semiconductors (PSs), we establish a two-dimensional (2D) deformation-polarization-carrier coupling bending model for PS structures, taking flexoelectricity into consideration. The analytical solutions to classical flexure of a clamped circular PS thin plate are derived. With the derived analytical model, we numerically investigate the distributions of electromechanical fields and the concentration of electrons in the circular PS thin plate under an upward concentrated force. The effect of flexoelectricity on the multi-field coupling responses of the circular PS plate is studied. The obtained results provide theoretical guidance for the design of novel PS devices.

In this study, the penetration resistance of a polyurethane elastomer (PUE)/honeycomb aluminum composite structure was investigated. A finite element analysis model was constructed to predict the residual velocity of the projectile after penetrating the PUE/honeycomb aluminum composite structure, and the accuracy of the model was verified through experiments. Both the residual velocity of the projectile and the failure appearance of the target plate were accurately predicted by the model. In addition, the Cowper–Symonds model was used to describe the material properties of the PUE layer, effectively simulating the damage appearance of the PUE layer after penetration. Subsequently, based on the validated model, three different configurations of the PUE/honeycomb aluminum composite structure were designed on the basis of the original honeycomb aluminum composite structure with a polyurethane elastomer coating, maintaining constant mass of the composite structure, and the ballistic performance was predicted using the finite element model. The anti-penetration performance of the PUE/honeycomb aluminum composite structure was analyzed by examining the velocity changes of the projectile, the energy changes of each component, and the crushing of the honeycomb core layer. Finally, the influence of different projectile shapes on the ultimate ballistic performance of the structure was studied, and the reasons for the influence of warhead shape on the appearance of target plate failure were analyzed.

The flexoelectric effect describes the interplay between material polarization and strain gradient. While much research has focused on control strategies for flexoelectricity, the impact of ferroelectric domain structure on the flexoelectric effect remains elusive. Through phase field simulations, we conduct a comparative study on the flexoelectric response of two types of BaTiO₃–SrTiO₃ binary films: BaTiO₃–SrTiO₃ multilayers and (Ba,Sr)TiO₃ solid solutions. Our findings reveal that the flexoelectric response of these two systems, at the same Ba/Sr ratio, differs not only in magnitude but also in other aspects like temperature dependence, linearity, and hysteresis, due to their different ferroelectric domain structures and evolution dynamics. Our study deepens our current understanding of flexoelectricity in ferroelectrics and suggests “domain engineering” as a potential way to tailor this effect.

Skin tissue is a kind of complex biological material abundant with fibers. A new constitutive model, relating macroscopic responses with microstructural fiber configuration alteration, is developed to investigate the stress softening behaviors of skin tissue observed during cyclic loading–unloading tests. Two influential factors are introduced to describe the impact of fiber configuration change and stretch-induced damage. The present model achieves good agreement between predicted stress distribution of human skin and corresponding ex vivo experimental data obtained from the literature, affirming its capability to effectively capture the characteristic softening behaviors of human skin under cyclic loading conditions.