Liang Li

This paper investigates the dynamic characteristics of rotating functionally graded material (FGM) micro-beams based on Euler–Bernoulli beam theory, Euler–Bernoulli beam theory incorporating shear deformation, and Timoshenko theory. The deformation field of the micro-beam is described within a floating coordinate system using the meshless point interpolation method (PIM/RPIM). The couple stress tensor and curvature tensor, which capture the size effect, are incorporated into the potential energy formulation. Employing Lagrange’s equations of the second kind, a higher-order rigid-flexible coupled dynamic model for rotating FGM micro-beams is established under various beam theories. Simulation results obtained from the Euler–Bernoulli theory with shear correction and the Timoshenko model are compared with those from the classical beam model and previous literature. The influences of material gradient index, material characteristic length parameter, and rotational speed profiles on the transient dynamic response and steady-state free vibration of rotating micro-beams are systematically examined. The results show that increasing the material gradient index reduces the structural stiffness, resulting in lower natural frequencies and larger vibration amplitudes, whereas increasing the characteristic length parameter enhances the size effect and improves system stiffness.

Elastic edge states, formed by interfacing different topological phases and appealing for various cutting-edge applications based on surface acoustic waves, often exhibit limits due to the lack of strong topological protection. Here, we overcome this difficulty by engineering a synthetic three-dimensional (3D) Dirac semimetal phase in a 2D elastic metamaterial. By tuning a geometry parameter, we drive topological transitions, which can be mapped into Dirac points in hybrid 3D, i.e., 2D plus a synthetic dimension. Gapless adiabatic spectral flows are found along the synthetic momentum loops when they encircle the Dirac points, emerging as the surface-arc states in hybrid 3D, that restores the bulk-edge correspondence in elastic systems. Experimental measurements confirm the bulk Dirac points, surface-arc states linking oppositely charged Dirac points, and the emergent gapless spectral flows. This Letter brings novel quantum-inspired phenomena to elastic systems and may inspire applications in topological control of mechanical waves and dynamics.

Addressing the urgent need for lightweight and reusable energy-absorbing materials in aviation impact resistance, this study introduces an innovative multi-directional braided metamaterial design enabled by 4D printing technology. This approach overcomes the dual challenges of intricate manufacturing processes and the limited functionality inherent to traditional textile preforms. Six distinct braided structural units (types 1–6) were devised based on periodic trigonometric functions (Y = A sin(12πX)), and integrated with shape memory polylactic acid (SMP-PLA), thereby achieving a synergistic combination of topological architecture and adaptive response characteristics. Compression tests reveal that reducing strip density to 50–25% (as in types 1–3) markedly enhances energy absorption performance, achieving a maximum specific energy absorption of 3.3 J/g. Three-point bending tests further demonstrate that the yarn amplitude parameter A is inversely correlated with load-bearing capacity; for instance, the type 1 structure (A = 3) withstands a maximum load stress of 8 MPa, representing a 100% increase compared to the type 2 structure (A = 4.5). A multi-branch viscoelastic constitutive model elucidates the temperature-dependent stress relaxation behavior during the glass–rubber phase transition and clarifies the relaxation time conversion mechanism governed by the Williams–Landel–Ferry (WLF) and Arrhenius equations. Experimental results further confirm the shape memory effect, with the type 3 structure fully recovering its original shape within 3 s under thermal stimulation at 80 °C, thus addressing the non-reusability issue of conventional energy-absorbing structures. This work establishes a new paradigm for the design of impact-resistant aviation components, particularly in the context of anti-collision structures and reusable energy absorption systems for eVTOL aircraft. Future research should further investigate the regulation of multi-stimulus response behaviors and microstructural optimization to advance the engineering application of smart textile metamaterials in aviation protection systems.

The frequency and buckling characteristics of functional gradient (FG) beams with asymmetric material distribution in the temperature field are analyzed in this paper. Generally, the asymmetrical material distribution of FG beams results in a non-zero neutral axis and non-zero thermal moment. However, some previous studies adopted the treatment of homogeneous beams in which the neutral axis and thermal moment were set as zero. To this end, a comprehensive FG beam model with thermal effect is developed based on the absolute nodal coordinate formulation, in which Euler–Bernoulli beam theory, Lagrangian strain, exact curvature, thermally induced strain, and neutral axis position are considered. For the convenience of comparisons, the presented model can be simplified into three models which do not consider the neutral axis or thermal moment. The numerical results indicate that the influence of the neutral axis on the thermal axial force is minimal while that on the thermal moment is significant. In the case of the high temperature difference, frequency, critical temperature difference, unstable state, and the buckling type of the FG beams are misjudged when the neutral axis or thermal moment is ignored.

When spacecraft execute missions in space, their solar panels—crucial components—often need to be folded, unfolded, and adjusted at an angle. These operations can induce numerous detrimental nonlinear vibrations. This paper addresses the issues of nonlinear and thermal-coupled vibration control within the context of space-based flexible solar panel systems. Utilizing piezoelectric smart hybrid vibration control technology, this study focuses on a flexible plate augmented with an active constrained layer damping. The solar panel, under thermal field conditions, is modeled and simulated using the commercial finite element simulation software ABAQUS. The research examines variations in the modal frequencies and damping properties of the model in response to changes in the coverage location of the piezoelectric patches, their coverage rate, rotational angular velocity, and the thickness of the damping layer. Simulation results indicate that structural damping is more effective when the patches are closer to the rotation axis, the coverage area of the patches is larger, the rotational speed is lower, and the damping layer is thicker. Additionally, the effectiveness of vibration suppression is influenced by the interplay between the material shear modulus, loss factor, and specific working temperature ranges. The selection of appropriate parameters can significantly alter the system’s vibrational characteristics. This work provides necessary technical references for the analysis of thermally induced vibrations in flexible solar sails under complex space conditions.