Acta Mechanica Sinica最新文献

Blasting-induced crack networks considerably impact the extent of rock fragmentation and the evaluative construction qualities of deep underground facilities. Based on the Hoek-Brown criterion, an integrated strategy of the Johnson-Holmquist (JH-2) model, failure criterion, and crack softening failure model was used to numerically explore the influences of borehole distance, time interval, and confining pressure on blasting crack propagation and coalescence. First, one-borehole blasting was used to reproduce the crack propagation results under free and non-reflecting boundaries, and the good results provided compelling evidence of the reliability of this strategy. For the two- and three-borehole blasting, it was discovered that high confining pressure paired with the large time interval was not favorable for crack coalescence. Therefore, simultaneous initiation is an optimal plan, which is not dependent on time interval and confining pressure. Simultaneously, if the borehole distance remains unvaried, the predominant influence on crack coalescence transitions from the time interval to the confining pressure as these two factors increase. Moreover, crack coalescence takes place when the tensile stress field of one crack is not converted into the compressive stress field of another crack, and crack coalescence has two key mechanisms: mutual and indirect modes. In addition, the dependence of controlling parameter on coalescence mode has been discussed.

This paper investigates the interfacial debonding along the fiber-electrolyte interface induced by fiber lithiation in carbon fiber structure batteries using a shear-lag model, with the model validated through finite element simulations. The results demonstrate that as lithiation progresses, the interface transitio00ns from a purely elastic state to a cohesive damage phase, ultimately leading to interfacial debonding. Once debonding initiates, cracks propagate rapidly along the fiber-electrolyte interface, impeding ion and electron transport and significantly degrading the electrochemical performance and load-bearing capacity of the battery. To mitigate interfacial debonding, this study systematically examines the impacts of electrode length, modulus of carbon fiber and solid-state electrolyte, and cross-sectional size ratio. The findings indicate that electrode length and carbon fiber modulus have limited impacts on interfacial debonding, while reducing the modulus of solid-state electrolyte effectively decreases shear stress at the interface, thereby inhibiting debonding. Furthermore, a smaller cross-sectional size ratio alleviates interfacial stress, reducing the possibility of debonding. This research offers theoretical insights for the design of carbon fiber-based batteries, particularly in enhancing their structural stability and performance under electromechanical coupling environment.

Metamaterials are materials whose unique properties are associated with their geometric structure rather than the chemical composition of the base material. These properties can be influenced at various scales but this work focuses on a cell’s topological defect. Samples for mechanical testing were printed using digital light processing lithography technology. One of the characteristics studied in this work is the rotation of the cell’s face under uniaxial loading. For both the regular cell and the cell with topological defect, the rotation was directed clockwise, which corresponds to the direction of twisting of the structures on the lateral faces. The maximum twisting angle of the regular cell is 0.84°. The introduction of topological defect reduced the twist angle of the cell by more than 30%. It was found that the force value in the cell with a topological defect is higher, indicating that the cell with the defect is more rigid than the cell without it.

The deformation of multilayer structures under external loadings provides both opportunities and challenges for modern manufacture. The stress and displacement fields are influenced by the structure’s geometrical configuration, material properties, and bonding conditions at the interfaces between adjoining layers. In this study, we investigate the mechanical response of a perfectly-bonded multilayer structure under normal loading using the Fourier transform. The normal loading is decomposed into symmetric and antisymmetric cases based on the linear superposition principle. Closed-form solutions are obtained in the formation of Fourier integrals with the associated coefficients being determined by the boundary conditions. The effects of Poisson’s ratio, shear modulus, and thickness on the stress distribution and maximum displacement are studied. For a two-layer structure, plastic deformation is most likely to initiate in the soft layer near the interface in the presence of a large shear moduli ratio between the two layers. Although the average normal displacement increases as the soft layer thickens, regardless of the shear modulus ratio, it may not increase monotonically with the total thickness, particularly when the shear modulus ratio is small. Under the thin film approximation, the response with uniform normal loading can be used to estimate the response of the indentation problem. The numerical model presented in this work provides a tool to analyze the deformation of multilayer structures under surface loadings.

Fiber-reinforced composite materials are widely used in engineering fields. The design of curvilinear fiber paths is significant for improving the mechanical and manufacturing performances of the composite materials. Therefore, this paper presents an optimization method for curvilinear fibers with stress and manufacturing constraints. The membrane-embedded model is adopted to simulate the composite materials because it does not require extensive constitutive tests. Curvilinear fiber paths are described using the parametric level set method, which naturally avoids the crossing of fiber tows. The fiber optimization model is to minimize structural compliance with stress and manufacturing constraints. Adjoint method is used to obtain the sensitivity information of the objective and constraint functions. Numerical examples demonstrate the effectiveness of the proposed optimization method. The structural stiffness of the optimized composites has been significantly increased while satisfying the stress and manufacturing constraints.

This paper presents a theoretical investigation into the dynamics of a transverse domain wall within a bilayer multiferroic heterostructure composed of a thick piezoelectric actuator and a thin magnetostrictive layer of hexagonal crystal symmetry. The study is based on the Landau-Lifshitz-Gilbert equation, accounting for the interplay of axial and transverse magnetic fields, spin-polarized electric currents, magnetoelastic effects, crystal symmetry, and piezo-induced strains. Explicit analytical expressions for key parameters, including polar angle, domain wall width, velocity, and displacement, are derived using a trial function inspired by the Schryer and Walker approach and employing the small-angle approximation. The results reveal that transverse magnetic fields, crystal symmetry, and piezo-induced strain are instrumental in modulating domain wall dynamics in the steady-state propagation regime. To be precise, the domain wall width directly depends on the transverse magnetic field strength, while the velocity is significantly enhanced under field-driven conditions, though it remains largely unaffected in current-driven motion. We emphasize that our findings align qualitatively well with recent theoretical and experimental observations, offering insights into tuning the dynamics of magnetic domain walls in multiferroic heterostructures.

This paper presents an experimental and theoretical study on Richtmyer-Meshkov instability at a light/heavy single-mode gaseous interface under reflected shock wave (reshock) conditions. Particular emphasis is placed on the influence of initial conditions (including shock strength, interface density ratio, and amplitude-to-wavelength ratio) on the perturbation growth following reshock. The results reveal that, for all cases, the interface amplitude exhibits a long-term linear growth with time after reshock, followed by a rapid decay in growth rate, highly similar to the perturbation growth behavior after single shock. Higher Mach numbers intensify transverse wave interactions with the interface, significantly affecting the interface morphology. Additionally, the interface is driven closer to the end wall, increasing the frequency of interactions between reverberating waves and the interface. This results in significantly enhanced mixing, as evidenced by the notably larger interface thickness, making the prediction of post-reshock growth rates across varying shock strengths particularly challenging. Interfaces with different density ratios demonstrate similar growth patterns, with the normalized perturbation growth showing near independence from the density ratio. As the amplitude-to-wavelength ratio increases, distinct transverse shock waves are generated after reshock, which produce high-pressure regions near the interface, causing the bubble head to present a cavity structure. For all cases, the early-stage post-reshock perturbation growth, when appropriately normalized, collapses well at the early stage but diverges at the late stage, especially for cases with varying Mach numbers. The linear superposition model, incorporating a reduction factor, effectively predicts the post-reshock growth rate for cases with different density ratios and initial amplitudes but loses precision for cases with varying shock strengths. Among existing models, the Sadot model (Sadot et al. 1998) offers the most reliable predictions for late-stage post-reshock perturbation growth.

Lateral jets play a crucial role in controlling the trajectory and aerodynamic heating of hypersonic vehicles. However, the complex interaction between turbulent and rarefaction effects has rarely been examined. This study fills this knowledge gap by employing the newly developed GSIS-SST method (Tian and Wu (2025)), which combines the shear stress transport (SST) model for turbulent flow and the general synthetic iterative scheme (GSIS) for rarefied gas flow. It is found that, at altitudes from 50 to 80 km, the maximum relative difference in the pitch moment between the GSIS-SST and pure GSIS (SST) reaches 28% (20%). While the jet is supposed to reduce the surface heat flux, its turbulence significantly diminishes this reduction, e.g., the GSIS-SST predicts a heat flux about one order of magnitude higher than the GSIS when the jet pressure ratio is 1.5. Increasing the angle of attack intensifies local turbulence, resulting in expanded discrepancies in shear stress and heat flux between GSIS-SST and GSIS. These insights enhance our comprehension of lateral jet flows and highlight the importance of accounting for both turbulent and rarefaction effects in medium-altitude hypersonic flight.

This paper investigates the dynamics of a railway wheelset system subjected to random excitation and governed by a displacement delay feedback controller. Initially, the delay component of the wheelset system was estimated utilizing standard form theory and center manifold theory. Subsequently, the differential equation characterizing the stochastic wheelset system was reformulated into a form that incorporates both amplitude and phase, employing the random averaging technique. The local stability of the wheelset system was subsequently assessed using the Lyapunov exponent method, while global stability was evaluated through singular boundary theory. Additionally, the random bifurcation characteristics of the wheelset system were examined using probability density function diagrams. Ultimately, numerical simulations were performed to analyze the influence of velocity and delay on the stochastic dynamics of the wheelset system, and the theoretical results were validated.

This paper investigates the contact problem of an air-inflated circular membrane with a finite rigid indentor having three different geometric profiles, namely flat-face, conical, and spherical. Initially, the axisymmetric inflation problem of a thin circular membrane is studied under uniform pressurization. The material is assumed to be homogeneous, isotropic, and incompressible, which is described by the two-parameter Mooney-Rivlin hyperelastic model. An indentor with finite radius is pressed quasi-statically against the inflated membrane, preserving the axisymmetric nature of deformation. The contact problem is formulated for both frictionless and no-slip contact conditions. A set of coupled nonlinear second order partial differential equations for both contact and non-contact regions are solved using a shooting method coupled with an optimization algorithm. The inflated membrane profiles in contact with different indentor geometries, principal stretch ratios, and Cauchy stress resultants are obtained. The possibility of having multiple contact zones and their interaction on different faces of the indentor is also explored. The force-displacement (stiffness) curves for this finite indentor contact problem show the existence of a critical contact force, which limits the force bearing capacity of the inflated structure. This critical force is found to be higher for larger strain-hardening of the material and higher indentor radius. The junction of contact and non-contact regions for flat-faced and conical indentors is found to be the critical section due to slope discontinuity. However, for the spherical indentor, the pole of the membrane is most prone to rupture due to membrane thinning effect.