Self-sustained motion has proven to be an effective approach for tackling complex problems and addressing various challenges across a variety of disciplines, such as bionics, soft robotics, and engineering, owing to its efficiency, resourcefulness, and flexibility. However, traditional single-mode self-sustained systems are often limited to specific tasks and lack adaptability to environmental changes. This study addresses these limitations by developing a multi-modal self-sustained system using circular silicone oil paper. It demonstrates that hot steam drives the silicone oil paper to achieve self-sustained motion, thereby constructing a self-sustained system. In this system, the circular silicone oil paper placed on a steam-supported surface continuously oscillates and tumbles under the influence of hot steam. The study analyzes the mechanisms behind these motions and establishes a geometric model for the self-sustained behavior of the circular silicone oil paper. Computational programming examines how the oscillation frequency and amplitude of the circular silicone oil paper relate to steam temperature and structural dimensions. Critical conditions for motion pattern transitions and phase diagrams are identified, with experimental studies validating theoretical predictions. The research findings reveal that by adjusting structural size and steam temperature, the circular silicone oil paper can freely switch among three modes: stationary, self-sustained oscillation, and self-sustained tumbling. The frequency and amplitude of self-sustained oscillation increase with higher steam temperatures, larger outer diameters, and an increased inner-to-outer diameter ratio. The multi-modal self-sustained system developed in this study can better adapt to diverse tasks and environments while reducing costs and energy consumption. Therefore, it holds significant potential for applications in fields such as autonomous robotics, medical devices, waste heat recovery, and thermo-mechanical conversion.

Under mechanical loading, metallic materials can fail in various ways, including yielding, fracture, buckling, wear, fatigue, and so on, with fracture being particularly destructive. Ductile fracture, characterized by dimples on the fracture surface, is commonly observed in pure metals and alloys. From the microscopic point of view, the ductile fracture of metals and alloys is closely associated with the nucleation, propagation, and coalescence of voids, influenced by factors such as stress state, void size, void volume fraction, void shape, and temperature. Micromechanics-based models developed for ductile damage considering the void evolution, such as the Gurson model and its extensions, usually presume spherical voids, but creating models that consider realistic void shapes and their evolution presents significant challenges. Moreover, conducting mechanical analyses of ductile failure across specimen and component scales requires addressing cross-scale issues. This study first constructed representative volume element models incorporating isolated voids of different initial shapes. Finite element simulations were carried out based on the representative volume elements by adopting a J2 plasticity model for the matrix, systematically analyzing how initial void shape affects stress-strain responses and ductile damage under triaxial tensile and shear loading conditions. A neural network-based surrogate model was trained with the numerical data generated by the simulations to approximate stress-strain responses and damage evolution. This model effectively predicted how initial void shape influences ductile damage. Subsequently, a user-defined material subroutine was developed and integrated into a commercial finite element code to simulate the impact of initial void shapes on the ductile failure process in notched specimens. Results indicated that a reduced aspect ratio for the voids decreased the damage rate, leading to delayed softening at the specimen level. This work demonstrates the potential of using surrogate models to predict ductile damage involving complex microstructural features.

Materials with negative Poisson's ratios, as typical mechanical metamaterials, exhibit indentation resistance when impacted, significantly enhancing their impact resistance while remaining lightweight and capable of high energy absorption. Previous research primarily focused on the mechanical properties of honeycomb structures under forward impacts, with limited studies on the dynamic response of multi-cell structures with negative Poisson's ratios—particularly those made of double material cells—under inclined loads. However, structural failures from inclined load impacts are unavoidable in engineering practice. This study integrates gradient design in multicellular structures with inclined load impacts to analyze energy absorption and crushing deformation modes of structures. We propose a gradient bimaterial negative Poisson's ratio honeycomb structure featuring a curved edge concave bimaterial cell. By changing the materials of the transverse and longitudinal curved bars, we design four types of material gradient honeycomb structures: positive gradient, negative gradient, symmetrical positive gradient, and symmetrical negative gradient. Using numerical methods, we examine the dynamic behavior of each gradient structure under in-plane oblique impact loading. It is found that the honeycomb structure with a negative gradient bimaterial arrangement performs best in energy absorption during oblique impacts. We detail the deformation mode, nominal stress-strain curve, and energy absorption of the negative gradient structure at different impact velocities and impact oblique angles. Results indicate that both impact velocity and impact oblique angle significantly affect energy absorption. Regardless of speed, the smaller the impact oblique angle, the better the energy absorption of the honeycomb structure, meaning crashworthiness decreases as the impact oblique angle increases.

In the topology optimization of compliant mechanisms, positional and shape factors significantly affect structural mechanical properties. The formation of concentrated hinge regions not only weakens structural strength but also hinders manufacturability. To this end, we propose a topology optimization method for hinge-free compliant mechanisms, incorporating geometric nonlinearity and utilizing the bi-directional evolutionary structural optimization (BESO) method. Initially, the design domain is discretized, where the 0-1 distribution of the BESO method prevents element distortion during nonlinear finite element analysis, thus enhancing numerical stability and convergence. The deformations of the compliant mechanism at the input and output are constrained under unit excitation, effectively suppressing the emergence of concentrated hinges. This leads to improved structural strength and manufacturability. Finally, hinge-free mechanisms are fabricated via additive manufacturing. Experimental results from samples show excellent agreement with finite element simulations, validating the effectiveness of the proposed hinge-suppression strategy in compliant mechanism design.

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.

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.

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.

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.

Magnesium (Mg), a lightweight metal material, is constrained in its applications due to poor plasticity and low strength at high temperatures. Graphene (Gr) possesses a large specific surface area and high strength, making it an ideal reinforcement for improving the mechanical properties of materials. A molecular dynamics (MD) simulation was employed to investigate the mechanical behaviors of single-crystal Mg and Gr/Mg composites under compressive loading. Through the analysis of stress-strain curves, atomic structure diagrams, and dislocation distributions, the microscopic deformation mechanisms of single-crystal Mg and Gr/Mg composites under compressive loading were explored. Additionally, the influence of factors such as the number of Gr layers, loading strain rate, and temperature on the mechanical properties of materials was studied. Results reveal that single-crystal Mg exhibits anisotropic characteristics under compressive loading. Addition of Gr enables the activation of difficult-to-initiate slip systems in the Mg matrix due to grain refinement. This leads to stress release and difficulty in initiating twinning deformation. Near the Gr interface, defects such as dislocations and twins nucleate and proliferate, effectively transferring the load to Gr, thereby elevating the average flow stress during the plastic deformation stage of the composites. Furthermore, the Mg matrix restricts the folding and bending of Gr, leading to an enhancement in material toughness. As a result, when the Gr/Mg composite is compressed along the [0 0 0 1] crystal direction to a strain of 0.35, the Gr remains intact without fracture. Dislocations in Gr/Mg composite materials cannot penetrate the Gr layer, thus suppressing Mg matrix damage. Increased dislocation lines can resist compressive plastic deformation. In composites featuring multiple layers of Gr, the yield stress, yield strain, and average flow stress during the plastic deformation stage increase with the number of Gr layers. Additionally, the yield strain is higher when Gr layers are separated compared to being stacked. Within the temperature range of 10 K-600 K, the elastic modulus and yield stress of Gr/Mg composites decrease with increasing temperature. However, the strain rate has a minor effect on the elastic modulus and average flow stress during the plastic deformation of Gr/Mg composites. Nonetheless, increasing the strain rate can enhance the yield stress and yield strain of the composites.

This study examines the tensile properties of skin suturing interfaces created through a silica gel reverse molding process, focusing on the reliability of clinical adhesive properties post-suturing. Four types of skin suturing interfaces, inspired by natural bionic structures, are designed, with primary attention on their tensile stiffness. An equivalent mechanical model is constructed using mechanical theories of suturing interfaces, and a theoretical model is developed to predict the tensile stiffness of each structure. Numerical simulations and physical experiments are conducted to analyze the brittle failure behavior and tensile failure modes of the suturing structures. The influences of shape factor, tooth tip angle, and tip region on the tensile properties of the interface are thoroughly investigated. A parameter mapping model using tensile strength as the evaluation index is constructed for each sensitive factor. It is found that the skin suturing interface exhibits brittle failure behavior, with the zigzag structure showing significantly higher tensile stiffness compared to other suturing structures. As the tooth tip angle increases, the stiffness of the suturing structure decreases, while the tip area enhances the tensile properties of the interface. These results are anticipated to help improve skin wound healing rate after clinical suturing.