Acta Mechanica Solida Sinica最新文献

Honeycomb structures of shape memory alloy (SMA) have become one of the most promising materials for flexible skins of morphing aircraft due to their excellent mechanical properties. However, due to the nonlinear material and geometric large deformation, the SMA honeycomb exhibits significant and complex nonlinearity in the skin and there is a lack of relevant previous research. In this paper, the nonlinear properties of the SMA honeycomb structure with arbitrary geometry are investigated for the first time for large deformation flexible skin applications by theoretical and experimental analysis. Firstly, a novel theoretical model of SMA honeycomb structure considering both material and geometric nonlinearity is proposed, and the corresponding calculation method of nonlinear governing equations is given based upon the shooting method and Runge–Kutta method. Then, the tensile behaviors of four kinds of SMA honeycomb structures, i.e., U-type, V-type, cosine-type, and trapezoid-type, are analyzed and predicted by the proposed theoretical model and compared with the finite element analysis (FEA) results. Moreover, the tensile experiments were carried out by stretching U-type and V-type honeycomb structures to a global strain of 60% and 40%, respectively, to perform large deformation analysis and verify the theoretical model. Finally, experimental verification and finite element validation show that the curves of the theoretical model results, experimental results, and simulation results are in good agreement, illustrating the generalizability and accuracy of the proposed theoretical model. The theoretical model and experimental investigations in this paper are considered to provide an effective foundation for analyzing and predicting the mechanical behavior of SMA honeycomb flexible skins with large extensional deformations.

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.

Nickel-based alloys are the primary structural materials in steam generators of high-temperature gas reactors. To understand the irradiation effect of nickel-based alloys, it is necessary to examine dislocation movement and its interaction with irradiation defects at the microscale. Hardening due to voids and Ni₃Al precipitates may significantly impact irradiation damage in nickel-based alloys. This paper employs the molecular dynamics method to analyze the interaction between edge dislocations and irradiation defects (void and Ni₃Al precipitates) in face-centered cubic nickel. The effects of temperature and defect size on the interaction are also explored. The results show that the interaction process of the edge dislocation and irradiation defects can be divided into four stages: dislocation free slip, dislocation attracted, dislocation pinned, and dislocation unpinned. Interaction modes include the formation of stair-rod dislocations and the climbing of extended dislocation bundles for voids, as well as the generation of stair-rod dislocation and dislocation shear for precipitates. Besides, the interactions of edge dislocations with voids and Ni₃Al precipitates are strongly influenced by temperature and defect size.

The stress wave profile at the frictional interface is crucial for investigating the frictional process. This study modeled a brittle material interface with a micro- contact to analyze the fine stress wave structure associated with frictional slip. Employing the finite element simulation alongside the related wave theory and experiments, two new wave structures were indentified: A Mach cone symmetric to the frictional interface associated with incident plane wave propagation, and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate. The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium. Consequently, a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence. The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface; instead, the frictional interface effect may be responsible for the generation of such new wave structures. The measured wave profiles provide a proof for the existence of the new wave structures. These results display new wave phenomena, and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.

Star-shaped lattice structures with a negative Poisson’s ratio (NPR) effect exhibit excellent energy absorption capacity, making them highly promising for applications in aerospace, vehicles, and civil protection. While previous research has primarily focused on single-walled cells, there is limited investigation into negative Poisson’s ratio structures with nested multi-walled cells. This study designed three star-shaped cell structures and three lattice configurations, analyzing the Poisson’s ratio, stress–strain relationship, and energy absorption capacity through tensile experiments and finite element simulations. Among the single structures, the star-shaped configuration r3 demonstrated the best elastic modulus, NPR effect, and energy absorption effect. In contrast, the uniform lattice structure R3 exhibited the highest tensile strength and energy absorption capacity. Additionally, the stress intensity and energy absorption of gradient structures increased with the number of layers. This study aims to provide a theoretical reference for the application of NPR materials in safety protection across civil and vehicle engineering, as well as other fields.

This paper presents an improved level set method for topology optimization of geometrically nonlinear structures accounting for the effect of thermo-mechanical couplings. It derives a new expression for element coupling stress resulting from the combination of mechanical and thermal loading, using geometric nonlinear finite element analysis. A topological model is then developed to minimize compliance while meeting displacement and frequency constraints to fulfill design requirements of structural members. Since the conventional Lagrange multiplier search method is unable to handle convergence instability arising from large deformation, a novel Lagrange multiplier search method is proposed. Additionally, the proposed method can be extended to multi-constrained geometrically nonlinear topology optimization, accommodating multiple physical field couplings.

This paper studies the vibration responses of porous functionally graded (FG) thin plates with four various types of porous distribution based on the physical neutral plane by employing the peridynamic differential operator (PDDO). It is assumed that density and elastic modulus continuously vary along the transverse direction following the power law distribution for porous FG plates. The governing differential equation of free vibration for a porous rectangular FG plate and its associated boundary conditions are expressed by a Lévy-type solution based on nonlinear von Karman plate theory. Dimensionless frequencies and mode shapes are obtained after solving the characteristic equations established by PDDO. The results of the current method are validated through comparison with existing literature. The effects of geometric parameters, material properties, elastic foundation, porosity distribution, and boundary conditions on the frequency are investigated and discussed in detail. The highest fundamental dimensionless frequency occurs under SCSC boundary conditions, while the lowest is under SFSF boundary conditions. The porous FG plate with the fourth pore type, featuring high density of porosity at the top and low at the bottom, exhibits the highest fundamental frequency under SSSS, SFSF, and SCSC boundary conditions. The dimensionless frequency increases with an increase in the elastic foundation stiffness coefficient.

Damped acoustic systems have a limited quality factor due to intrinsic loss. By introducing gain elements, a method to enhance the quality factor of damped systems is proposed based on the concept of bound states in the continuum (BICs). The acoustic model under study is a two-port waveguide system installed with two side Helmholtz resonators connected by a coupling tube. Based on the temporal coupled-mode theory, a Hamiltonian matrix with both intrinsic and radiation losses is used to characterize the resonance behavior of the coupled resonators. To achieve a high quality factor, acoustic gain is introduced to compensate the intrinsic loss, leading the Hamiltonian parameters toward a quasi-BIC condition. Numerical simulation demonstrates a gain-assisted and quasi-BIC-supported extremely high quality factor in damped acoustic systems. The concept is further utilized to design a sensor model for particle size detection. The enhanced sensing performance due to high quality factors is numerically demonstrated. The findings suggest potential applications in acoustic sensing and detection devices.

This paper investigates the effect of hydrogen on the transformation ratcheting of NiTi shape memory alloy (SMA) wires in the experimental and theoretical aspects. In the aspect of experiments, the NiTi SMA orthodontic wires are hydrogen charged by the electrochemical charging method at room temperature with varying charging durations and charging lengths. After that, the ex-situ cyclic tension-unloading experiments are performed for the charged and non-charged wires. Experimental results reveal that the two transformation platforms (two-step MT) occur during the forward MT at the beginning and end of cyclic deformation for hydrogen-charged wires, which can be regarded as a global response of the non-charged and charged regions. Furthermore, this two-step MT and transformation ratcheting aggravate with the increase of the charging duration. In the aspect of the theoretical model, a diffusional-mechanically coupled constitutive model is developed. In this constitutive model, the strain is considered as four components: elasticity, transformation (MT), hydrogen expansion and transformation-induced plasticity (TRIP). Combining Helmholtz free energy and Clausius–Duhem inequality, the thermodynamic driving forces of MT and TRIP are obtained. Fick’s law and the mass conservation equation are incorporated to derive the evolution of hydrogen concentration. A transition from material points to the whole wire is employed to extend the model from a material point to the entire wire, and the overall response with a heterogeneous hydrogen concentration field is obtained. The proposed model's ability to predict the transformation ratcheting of the non-charged and charged NiTi SMA wires is verified by contrasting predictions and experimental results.

Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting (HTS) cables. Various winding core structures can influence the mechanical–electrical behavior of cables, but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear. This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension. The three cables analyzed are CORC (conductor-on-round-core), CORT (conductor-on-round-tube), and HFRC (conductor-on-spiral-tube). A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio. Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable, aligning with experimental data. Among the three cables, the HFRC cables exhibit the weakest resistance to transverse deformation. However, the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable, provided that the transverse compression properties are maintained. Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables. Meanwhile, the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties. It recommends utilizing small tape gaps, lower frequencies, and spiral core construction to minimize eddy losses. The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.