The negative Poisson's ratio honeycomb structure is widely used in the field of impact protection because of its unique mechanical properties and excellent energy absorption capacity. The evolution of local dynamic stress in this structure is closely related to changes in its cellular microstructure under dynamic impact. Current research on negative Poisson's ratio structures mainly focuses on improving overall energy absorption capacity of the structure by designing cells with concave deformation mechanism, often ignoring the structural optimization of existing models and lacking exploration of other energy absorption mechanisms of rotary deformation. To further improve the dynamic response of star-shaped honeycomb structures with negative Poisson's ratio under in-plane impacts, the rotation characteristics of cells are studied in this paper. Building on traditional designs, the star-shaped honeycomb structure is further optimized, and the deformation energy absorption mechanism of star-shaped honeycomb cell is endowed with the coupling idea. Based on the principle of relative density equality, two types of rotating star-shaped cellular cells with double negative Poisson's ratio effect are obtained by internal rotation and external rotation: internal star-shaped cellular cells and external star-shaped cellular cells. The energy absorption characteristics of different honeycomb structures under in-plane impact loads are studied using numerical simulations, and the influences of both concave and rotating deformation mechanisms on the energy absorption characteristics of honeycomb structures are investigated. Based on one-dimensional shock wave theory and energy absorption efficiency method, empirical formulas for dynamic platform stress and dense strain of star-shaped honeycomb structures are given, and the formulas for calculating their relative density are established. According to the theory of critical velocity, the first and second critical velocities of the star-shaped honeycomb structure are determined. The dynamic response of the rotating star-shaped honeycomb structure under different impact velocities is analyzed using the explicit dynamic finite element method. Simulation results are compared and analyzed with the evaluation indexes of model macro and micro deformation modes, platform stress, and specific energy absorption. The results show that when the new structures are impacted, their cells first rotate and then recess, exhibiting a stronger negative Poisson's ratio effect. Under the impact at a medium speed of 20 m/s, the platform stress of the internal honeycomb structure is higher and the stress stability is better. In the platform stage, the stress fluctuation of the external spiral honeycomb structure is more severe, but it has higher specific absorption energy under the impact at a high speed of 120 m/s. This study shows the relationship between the concave mechanism and rotation mechanism of the star-shaped honeycomb structure and its energy absorption characteristics, providing new insights for optimizing the impact dynamic performance of honeycomb structures.

The study of data-driven predictions for constraint-related fracture toughness is an interdisciplinary scientific problem relevant to mechanics, mechanical engineering, as well as computer science and technology, and is of great significance for accurate structural integrity assessment. This research focused on nuclear power steel A508. The predictive capabilities of four algorithms, namely the K-nearest neighbors (KNN) regression, kernel regression (KR), linear regression (LR), and random forest (RF) regression, for constraint-related fracture toughness predictions were investigated. The RF algorithm outperformed the others, while the KR algorithm had the least effective predictions. The prediction accuracy ranked as follows: RF>LR>KNN>KR. Furthermore, based on the RF algorithm, data under plane strain conditions were added for data enhancement, enabling the prediction and verification of constraint-related fracture toughness for single-edge notch bending (SENB) specimens. The validated model was successfully transplanted to single-edge notch tension (SENT), compact tension (CT), and central crack tension (CCT) specimens. Results indicated that the RF algorithm with data augmentation improved prediction accuracy and capability, particularly at boundary points. The RF-based model, enhanced with additional data strategies, demonstrated strong generalization across different specimen types. For SENB and CT specimens, bending loads dominate at the crack tip; thus, altering a/W and B/W enhances restraint. For SENT and CCT specimens, where shear loads predominate at the crack tip, adjusting a and B proves more effective. Finally, a unified, high-accuracy prediction model was developed by incorporating sample category features using the RF algorithm and data enhancement strategies.

Simulating three-dimensional (3D) crack propagation in solid structures poses significant challenges due to the unpredictability of crack paths, complicating both computation and solution strategies. Traditional methods often face difficulties in accurately capturing arbitrary crack propagation during large deformations. The finite particle method (FPM), based on vector mechanics, offers a novel numerical approach for analyzing complex behaviors in solid mechanics. Different from conventional continuum-based methods, FPM discretizes the solid domain into a collection of finite particles, each governed by Newton's second law of motion. This particle-based formulation enables seamless transitions between continuum and non-continuum behaviors by dynamically adding or removing particles, providing significant advantages for crack propagation analysis in both static and dynamic scenarios. In this study, the FPM is extended to address the dynamic fracture in 3D solids, focusing on the challenges related to crack initiation, propagation, and branching. The FPM is combined with an extrinsic cohesive zone model (CZM) to capture the complex behaviors of fractures, avoiding the need to pre-define crack paths and effectively managing discontinuities caused by crack propagation. A discriminant criterion is developed to identify the onset of crack initiation, and an automated embedding process for cohesive elements is implemented to enable real-time simulation of fracture surfaces. To manage the evolving topologies that arise from crack propagation, we propose a general strategy based on an ergodic search algorithm, which updates the connectivity of the discretized solid model dynamically as cracks evolve. In addition, we develop a GPU-based parallel solver using the CUDA toolkit to significantly accelerate fracture computations. The accuracy and applicability of the proposed method are validated through several numerical examples, including fracture simulations of plates and beams subjected to dynamic loading. The results demonstrate the capability of the method to accurately capture the intricate details of crack initiation, growth, and interaction in 3D solids. This extended FPM framework serves as a robust tool for analyzing dynamic fractures in engineering applications, providing a versatile framework for studying delamination, material failure, and structural collapse in both research and practical settings.

The connection conditions and vibration suppression methods of coupled shell structures have received much attention, particularly as these structures play a crucial role in aero-engine components. In this paper, the vibration characteristics of a rotating hard coating damping double-thin-walled cylindrical shell coupled structure under bolt connection conditions are studied. First, a discontinuous arc connection is constructed to simulate actual bolt connection conditions by improving the artificial spring distribution method of the continuous entire circumference. And the artificial spring technique is used to define the boundary conditions of the shell structure. Next, the strain energy of the hard-coating shell structure is determined based on Sander's shell theory. The effect of rotational speed is considered, and the Rayleigh-Ritz method is used to derive the dynamic equations of the shell structure. In addition, the efficient state space method is used for calculation. The rationality and accuracy of the theoretical methods are validated through literature comparisons and finite element analysis. Additionally, the effects of rotational speed, connection stiffness, hard-coating thickness, and boundary conditions on the traveling wave vibration characteristics of the shell structure are analyzed. The results show that the traveling wave frequency increases significantly when the connection stiffness is in the range of 10⁸～10¹⁰. Besides, the rotation leads to a separation phenomenon and an overall increasing trend in the traveling wave frequency. A greater hard coating thickness notably impacts the traveling wave frequency, exhibiting a maximum increase of 5.87% in the traveling wave frequency when the hard-coating thickness rises from 0 to 0.85 mm. These findings provide valuable theoretical insights and data support for the engineering design of hard-coating coupled double-thin-walled cylindrical shell structures.

This study investigated the dynamic response of continuous-density-graded aluminum foam sandwich tubes subjected to internal explosion loads. A finite element model for continuous-density-graded aluminum foam and sandwich tubes was established in polar coordinates using 3D-Voronoi technology. The influences of core density distributions, such as positive-gradient, negative-gradient, and V-shaped gradient including middle-high-gradient (high in the middle and low at both ends) and middle-low-gradient (low in the middle and high at both ends), core density gradient, assembly methods of tube walls and the core, and the length-to-diameter ratio of explosives on the anti-shock performance of the sandwich tube structure were analyzed. Results demonstrate that, for the same core density gradient, the maximum deformation of the outer tube in the sandwich tube with a negative-gradient core is the least, while the sandwich tube with a middle-low-gradient core exhibits the highest specific energy absorption, and the sandwich tube with a middle-high-gradient core shows the weakest anti-shock performance. As core density gradient increases, the maximum deformation of the outer tube in the sandwich tube with a negative-gradient core significantly decreases. The specific energy absorption for the sandwich tube with a middle-low-gradient core rises initially before declining, while the anti-explosion performance of the sandwich tube with a middle-high-gradient core deteriorates. Optimal bonding between tube walls and the core effectively improves the specific energy absorption of sandwich tubes with a uniform, negative-gradient, or middle-low-gradient core, but it also increases the maximum deformation of the outer tube. For varying length-to-diameter ratios of explosives, the maximum deformation of the outer tube in the sandwich tube with a negative-gradient core is smaller. The present work aims to provide valuable insights for designing such structures for protective engineering applications.

The fractional-order constitutive model traditional integer-order model in fields due to its fewer parameters and clearer physical meaning. In this study, the fractional-order standard linear solid model is adopted to deeply explore the linear creep buckling characteristics of viscoelastic thin plates under the force-coupling effect. To ensure the accuracy of numerical analysis, the Hermite-type radial basis function (HRBF) is used in this study. The calculation results high accuracy. that the stability of fractional-order viscoelastic thin plates significant time. Specifically, as time progresses, both the critical load and critical temperature of the thin plate show a downward trend, while the deformation displacement after buckling continuously increases.

Aircraft ground handling is significantly impacted by shimmy, which reduces landing gear lifespan and increases accident rates. This study employs a nonlinear energy sink (NES) to mitigate landing gear shimmy. Focusing on the landing gear of a light aircraft, a dynamic model incorporating an NES device is developed. First, the NES device's impact on the stability region and amplitude of landing gear shimmy is analyzed, demonstrating its effectiveness in mitigating shimmy. Beside, the study examines how parameters such as nonlinear stiffness, linear stiffness, mass, damping coefficient, and vertical distance from the NES device to the landing gear's S-axis influence damping. Furthermore, under specified optimization goals, suitable parameter ranges are selected and a genetic algorithm is employed for global optimization. Finally, the reliability of the optimized results is confirmed through time-domain analysis. This research indicates that NES devices can enhance landing gear anti-shimmy performance, offering significant practical value.

This study investigates the electromechanical characteristics of a conical dielectric elastomer actuator in a non-ideal state, specifically focusing on the dielectric constant related to tensile deformation. By using the Ogden elastic strain energy function with multiple material constants and incorporating a linear permittivity that depends on the tensile rate, the constitutive relation for a non-ideal state is further deduced. The model is solved employing the shooting method, allowing for analysis of the mechanical performance and electromechanical stability of conical dielectric elastomers. We observe significant out-of-plane nonlinear axisymmetric deformation when the membrane is subjected to external force and external voltage, both with and without pre-stretch. By changing the voltage while maintaining constant external force, we identify model parameters and assess how varying electrostriction coefficients impact radial strength, circumferential stretch, and the true electric field. As the electrostriction coefficient decreases, tensile deformation in the membrane becomes increasingly uniform under no pre-stretch conditions, and the true electric field distribution tends to become more even. Under prestretch conditions, tensile deformation in the membrane remains stable, and the true electric field distribution is more consistent. When the electrostriction coefficient is sufficiently small, both the tensile deformation and the true electric field distribution tend to be stable, enhancing the overall stability of the dielectric elastomer. It is found that the prestretch condition exhibits greater stability than the no pre-stretch scenario. This research enhances our understanding of the electromechanical properties in non-ideal states, providing a theoretical foundation for the stable operation of conical dielectric elastomers in practical applications. The findings can guide the design of conical dielectric elastomer actuators, assisting engineers in optimizing design parameters to improve the performance and reliability of actuators.

Thin-walled metal components frequently undergo multiaxial bending fatigue during operation, necessitating an experimental method to replicate loading conditions for investigating material properties. In this study, a novel biaxial bending test method using ultrasonic fatigue technology was proposed. The design involved a cruciform TC4 titanium alloy specimen tuned to a natural frequency of 20 kHz based on the principle of harmonic vibration, featuring vertically superimposed fourth-order and third-order bending modes to ensure the maximum stress region remained in the test section. Arc transitions were utilized in other regions to mitigate stress concentration. Finite element simulations and strain gauge tests were conducted to calibrate stress amplitudes in the specimens. Analysis of S-N curves, crack propagation paths, and fracture morphologies revealed the failure mechanisms of biaxial bending fatigue in the very high cycle regime under varied loading conditions. It was found that TC4 titanium alloy exhibited no fatigue limit in the very high cycle regime, showing a continuous downward trend. Owing to gradient stress distribution, biaxial bending fatigue demonstrated significantly longer fatigue life compared to uniaxial ultrasonic fatigue. Meanwhile, crack propagation behavior resembled conventional biaxial fatigue, producing H-shaped or Y-shaped cracks. Fracture surfaces exhibited a brittle characteristic in a large area of the crack initiation zone, with morphology primarily characterized by facets and tearing ridges formed through facet coalescence. In contrast to uniaxial bending fatigue, the facets in biaxial bending showed a batten pattern akin to multiaxial fatigue failure.

This study focuses on the aerothermoelastic characteristics of composite laminated panels with fully simply-supported boundaries in supersonic airflow, implementing macro fiber composites (MFCs) for active flutter-boundary control. In modeling the equation of motion, the influence of in-plane thermal load on transverse bending deflection is considered, and the aerodynamic pressure in supersonic airflow is calculated on the basis of supersonic piston theory. Motion differential equations of the structural system are derived from classical laminated plate theory and Hamilton's principle with the assumed mode method, then transformed into state space equations. By solving the state matrix eigenvalues, natural frequencies of the structural system are obtained. Aerothermoelastic characteristics of the laminated panel are analyzed via the frequency domain method, assessing the effects of ply angle and geometric parameters of the laminated panel on critical flutter aerodynamic pressure and critical buckling temperature. The proportional feedback control method is used to design the controller, and flutter boundaries of the laminated panel are computed under different control gain coefficients. Results demonstrate that the laminated panel with a ply angle of [90°/-90°/90°] exhibits the lowest aerothermoelastic stability across various aspect ratios. For larger ply angles, an increase in aspect ratio enhances the aerothermoelastic stability of the laminated panel. Adjusting MFC ply angles effectively increases critical flutter aerodynamic pressure. Moreover, the proportional feedback control method can significantly enhance flutter boundaries, but the control gain coefficient requires to be adjusted to ensure stability and performance of the control system. A control gain coefficient that is too small results in weak control, while one that is too large can destabilize the structural system.