Acta Mechanica Solida Sinica最新文献

The ablation behavior of ZrC-coated C/C composites is a complex coupling process involving thermal, mechanical, chemical interactions, formation and propagation of cracks. In the present study, we propose a peridynamic (PD) thermo-mechanical-oxidation-diffusion coupled model to describe such a phenomenon comprehensively. Firstly, motion and heat transfer equations are formulated, incorporating growth strain governed by the Clarke model. The oxidation rate of the material is evaluated using diffusion equilibrium and oxidation equations. In addition, the effects of oxidation on different materials are considered, such as growth strain in ZrC materials and material consumption caused by oxidation of C/C composites. To characterize the material failure caused by mechanical and chemical reactions in ablation, a porosity criterion is proposed and its effect on diffusion is considered. The reliability and accuracy of the proposed PD model are validated by analyzing the oxidation process of C/C composites and ZrC and comparing with experimental results. Further, the model effectively captured the crack propagation and oxidation of ZrC-coated C/C composites in an oxyacetylene environment.

The dynamic deformation behaviors of aluminum alloy sheets often differ from the quasi-static ones. Here, a dynamic biaxial tensile experiment of cruciform specimens has been proposed with electromagnetically actuated punch. A notched cruciform specimen was adopted to obtain heterogeneous deformation covering from equal-biaxial tensile to uniaxial tensile strain path. The inverse identification was used to determine the parameters of Hill48 and YLD2000-2D anisotropic yield functions for 5052-O aluminum alloy sheet. The YLD2000-2D anisotropic yield function was validated by comparison of the simulated and experimental principal strains. By comparison with the anisotropic yield functions under quasi-static loading conditions, the anisotropic yielding behaviors of 5052-O aluminum alloy sheet are alleviated under dynamic loading conditions.

The Hall effect of elastic waves has attracted much attention due to its unique properties. A hexagonal lattice phononic crystal plate model is designed in this paper. By changing the spatial symmetry of the unit cell, a band gap for the A₀ Lamb wave is opened. The existence of the edge state of the phononic crystal plate is obtained by finite element simulation. It is found that both zigzag-type edge and bridge edge are topological edge states by analysis of the band structure of the supercell. A rectangular model with a straight channel is designed and the simulation results show that the two types of channels are topologically protected only for the A₀ mode Lamb wave but not for the S₀ mode. In addition, the results of numerical simulation are verified by experimental data measured by a laser vibrometer. Finally, it is found that neither upside V-shaped channels nor channels with defects will affect the stable propagation of A₀ Lamb waves along the proposed route. This proposed model and method are helpful in broadening the means of regulating elastic waves in phononic crystal structures, and extending practical application of topological edge states in such structures.

Understanding the friction behavior between hexagonal boron nitride (h-BN) and water is critical for the potential applications of h-BN in liquid-related functional devices. By using a density-functional-theory (DFT)-based machine learning (ML) technique combined with long-time ML-parameterized molecular dynamics simulations, we have systematically investigated charge transfer and friction at the interfaces between h-BN and water. The introduction of defects (including Stone-Wales, B-vacancy, N-vacancy, and B-vacancy/N-vacancy defects) into h-BN significantly enhances heterogeneous charge polarization and distribution at h-BN layers, as well as increases the friction coefficients at water/h-BN interfaces compared to perfect h-BN. The observed increase in interfacial friction of defected h-BN can be attributed to stronger charge transfer and higher charge density at the defected h-BN layers induced by interactions with water molecules. Our results offer deeper insights into the role of defects in modulating charge exchange and transfer between water and h-BN, as well as their impact on interfacial friction.

This paper presents a novel fully edge-based smoothed finite element method for free vibration analysis of functionally graded plates, incorporating a quasi-weak form of smoothed integral within an edge-based finite element method framework. Employing first-order shear deformation plate theory, the present method accounts for transverse shear strain and rotary inertia effects while addressing exponentially graded material properties along the plate thickness. The formulation integrates a three-node Mindlin plate element (MIN3) with a shear stabilization technique to prevent shear locking. The quasi-weak form of smoothed integral necessitates the evaluation of indefinite integrals for shape functions, effectively tacking domain integrals related to the shape functions without partial derivatives. By applying both quasi-weak form of smoothed integral and strain smoothing technique, all domain integrals in stiffness and mass matrices are converted into boundary integrals over smoothing domains. Therefore, isoparametric mapping and computing of Jacobian matrix are completely eliminated throughout the solution process. The natural frequencies obtained using the present method are in good agreement with those reported in the literature, highlighting the versatility of the present method for free vibration analysis of functionally graded plates. Notably, the present method demonstrates advantages in eliminating shear locking and reducing sensitivity to mesh distortion.

Bidirectional functionally graded (BDFG) beams are a promising solution for spacecraft structures subjected to extreme thermal and vibrational environments due to their superior thermal performance and design flexibility. Therefore, developing an efficient and highly convergent thermal vibration analysis method for BDFG beams under complex temperature fields is of paramount importance. This paper proposes a Chebyshev spectral method based on Reddy’s higher-order shear deformation theory (HSDT) to investigate the thermoelastic vibrations of BDFG beams. The material properties are temperature-dependent and vary with both thickness and length. The proposed method is validated by comparing the results with those in the existing literature. The analysis reveals that the critical buckling temperature rise is primarily influenced by the ceramic content, but thermal buckling can be mitigated by adjusting the material distribution. A trade-off exists between suppressing thermal buckling and relaxing thermal stresses, necessitating a balanced approach. The titanium alloy BDFG beam offers a broader design envelope compared to the metal-ceramic BDFG beam. The method presented in this study will provide theoretical support and guidance for the design of BDFG beams.

The recovery stress of materials has a great potential application in the field of road crack self-repair, composite material self-repair, and so on. Taking into account the diversity of practical application environments, the recovery stresses of constrained shape memory alloy (SMA) materials in the initial state of austenite and twinned martensite are given respectively in this paper. As for the experimental research, the austenitic SMA is loaded and constrained. The recovery stresses at different stages are observed by increasing the temperature. In terms of the theoretical research, constitutive models with the initial state of austenite and martensite are established respectively based on the one-dimensional macroscopic phenomenon theoretical model and constraints of SMA. These constitutive models can describe the relationship between recovery stress and volume fraction of martensite under temperature loading with different pre-strains. The theoretical model and experimental data in this paper can provide specific support for the practical engineering application of SMA recovery stress.

Fretting fatigue in bolted joints within aero-engine fan and compressor structures, characterized by multi-layered, thin-walled components and high preload, poses a significant structural safety challenge. This study investigates fretting fatigue in a bolted joint configuration simulating compressor axis contact with sealing disk ends, analyzing hysteresis loops, fretting scars, and fracture surfaces. Numerical simulation, incorporating a UMESHMOTION subroutine, and a critical plane approach utilizing the Smith-Watson-Thorpe parameter and Miner’s law, alongside wear morphology simulation, were employed to evaluate fretting fatigue life. Results revealed a non-monotonic relationship between surface quality and fretting fatigue life, demonstrating an initial life decrease followed by an increase, primarily due to a transition from partial to gross slip. The study highlights the significant impact of fretting on the life prediction of aero-engine bolted joints, demonstrating that improved surface quality does not always guarantee enhanced fatigue performance. The accuracy of the life prediction approach was validated through experimental correlation with wear-aware simulation results.

Polyethersulfone (PES) can be widely used in extreme environments due to its exceptional strength and stability. In this study, molecular dynamics (MD) simulations were used to construct tribological models of PES under varying pressures. The variations of PES molecular chains and frictional interface properties were explored for understanding microscopic tribological mechanism. The simulation results show that high pressure and high vacuum conditions reduce the coefficient of friction and wear rate. The variations in radial distribution function (RDF), relative concentration of atoms, friction interface temperature, and atomic motion velocity were analyzed. It was found that high pressure and high vacuum promote PES molecular chains moving away from the surface of the iron atomic layer, decreasing interaction energy, RDF, temperature, and velocity at the friction interface. This work offers novel methodologies and theoretical insights for studying the friction and wear of polymer composites in complex environments.

Fluid-conveying pipes have been widely used in diverse engineering fields, particularly in aerospace systems, nuclear power plants, oil transportation infrastructure, and biomedical devices. The recent advancements in 3D printing and materials science have increased research interest in the stability and vibration characteristics of slender pipes fabricated from hard magnetic soft (HMS) materials for magnetic control applications. Although several theoretical investigations have been conducted on magnetically controlled cantilevered fluid-conveying pipes, the understanding of their dynamical behavior in vascular environments remains incomplete. In this study, we investigate the buckling and dynamical behaviors of an HMS pipe under the combined effects of an applied magnetic field and nonlinear distributed spring constraints. By solving the nonlinear governing equation, natural frequencies, critical flow velocities, buckling displacements, and dynamic responses of the HMS pipe conveying fluid are obtained. The analysis reveals that the addition of distributed spring constraints leads to a substantial reduction in both buckling and dynamic displacements of the pipe system. Under constant magnetic field conditions, the pipe exhibits static deformation characteristics even when exposed to flow velocities exceeding the critical threshold for buckling instability. When subjected to an alternating magnetic field, the pipe system exhibits periodic oscillatory behavior across a wide range of flow velocities. This periodic response is characterized by displacement variations that show direct correlation with changes in the magnetic declination angle. Notably, nonlinear resonance phenomena associated with the first-mode natural frequency can occur even when the flow velocity is below the threshold for buckling instability. These results demonstrate that both magnetic field strength and declination angle offer a possible means for adjusting the stability, buckling behavior, and dynamic response of an HMS pipe.