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2024 Vol. 45, No. 6
Published: 2024-12-28
709
Bi-evolutionary Structural Optimization Method for hinge-free compliant mechanism considering geometric nonlinearity
Based on the Bi-evolutionary Structural Optimization(BESO) method, a design method for hinge-free compliant mechanisms considering geometric nonlinearity is proposed. Firstly, BESO method based on discrete topological variables and asymptotic evolution algorithm is adopted for the design of compliant mechanisms, which naturally avoids the distortion phenomenon of medium and low density elements in traditional variable density methods when considering geometric nonlinearity, and effectively improves the numerical stability of the topological evolution process. Secondly, by constraining the response deformation of the input and output terminals under unit excitation, the formation of concentrated hinges in the compliant mechanism is effectively suppressed, the structural strength is improved, and the manufacturability of the design configuration is improved. Linear and nonlinear compliant mechanism test samples were prepared separately, and the consistency between experimental and numerical simulation performance was good, demonstrating the necessity of considering geometric nonlinearity in topology optimization design of compliant mechanisms.
2024 Vol. 45 (6): 709-723 [
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724
Development of biaxial ultrasonic bending fatigue test method
To address the demand for long-life durability tests on thin-walled materials like aeroengine blades, this paper proposes an ultrasonic accelerated fatigue testing method suitable for biaxial bending fatigue experiments. Starting from the principle of simple harmonic vibration, a TC4 cross biaxial ultrasonic fatigue specimen with a natural frequency of 20 kHz, designed for both fourth and third-order bending vertical superposition, was developed. The vibration frequency and modes of this method were determined using strain gauges, and the stresses in ultrasonic bending fatigue were calibrated using a laser sensor. The study conducted experimental validations of very-high-cycle fatigue performance under biaxial bending loading. By analyzing the S-N curves, crack propagation paths, and fracture morphologies under different loading conditions, the characteristics of biaxial bending very-high-cycle fatigue failure behaviors were revealed.
2024 Vol. 45 (6): 724-734 [
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735
Thermomechanical Coupled Creep Buckling Analysis of Viscoelastic Thin Plates Based on the Fractional Standard Linear Solid Model
The fractional-ordered constitutive model, with its fewer parameters and clearer physical implications, has demonstrated superior applicability in numerous fields compared to traditional integer-ordered models. This study adopts the fractional standard linear solid model, aiming to delve into the linear creep buckling characteristics of viscoelastic thin plates under the coupled mechanical and thermal influences. To ensure the accuracy of the numerical analysis, the HRBF meshless method is employed, and the computational results have been verified for their high precision. The findings reveal that the stability of fractional viscoelastic thin plates exhibits a significant dependence on time, characterized by a decreasing trend in both the critical load and critical temperature of the plates as time progresses.
2024 Vol. 45 (6): 735-747 [
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16
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759
Nonlinear Energy Sink enhances the stability and suppression effect of nose landing gear shimmy
Aircraft ground handling is severely affected by shimmy, significantly reducing the landing gear's lifespan and increasing accident rates. To mitigate landing gear shimmy, this study employs a Nonlinear Energy Sink (NES).We focus on the landing gear of a light aircraft, a dynamic model incorporating an NES device is developed. First, we analyzes the NES device's impact on the stability region and amplitude of landing gear shimmy, demonstrating its effectiveness in mitigation. 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 the damping effect. Furthermore, under specified optimization goals, We had selected suitable parameter ranges 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, it’s offer significant practical value.
2024 Vol. 45 (6): 759-775 [
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21
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776
Molecular Dynamics Study of the Effect of Graphene on the Compressive Properties of Magnesium Matrix Composites
Magnesium (Mg), a lightweight metal material, is constrained in its applications due to its poor plasticity and low strength at high temperatures. Graphene (Gr) has the characteristics of large specific surface area and high strength. It is an ideal reinforcement for improving the mechanical properties of materials. Molecular dynamics (MD) simulation was employed to investigate the mechanical behaviors of single-crystal magnesium (Mg) and graphene/magnesium (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 the materials was studied. The results reveal that single-crystal Mg exhibits anisotropic characteristics under compressive loading. The addition of Gr enables the activation of difficult-to-initiate slip systems in the Mg matrix due to grain refinement. This leads to that stress is released, and the twinning deformation mechanism becomes difficult to initiate. Near the Gr interface, defects such as dislocations and twins nucleate and proliferate, effectively transferring the load to Gr, which elevates 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, which suppresses the damage of the Mg matrix. And the increase of dislocation lines can resist compressive plastic deformation. In composites with multiple layers of Gr, the yield stress, yield strain, and average flow stress during the plastic deformation stage increase with the increase in the number of Gr layers. Additionally, the yield strain is greater when the Gr layers are in a separated state compared to that in a stacked state. Within the temperature range of 10K-600K, the elastic modulus and yield stress of the Gr/Mg composite decrease with increasing temperature. However, the strain rate has an insignificant effect on the elastic modulus and average flow stress during the plastic deformation stage of the Gr/Mg composites. Nonetheless, increasing the strain rate can enhance the yield stress and yield strain of the composites.
2024 Vol. 45 (6): 776-794 [
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14
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795
Study on plane tensile properties of skin suture interface with structural parameterization
In view of the reliability of the tensile ability of the clinical adhesive after suturing the skin wound, the tensile properties of the skin suturing interface prepared by silica gel reverse molding process were studied. Based on the study of the tensile stiffness of four types of stitched structures, the equivalent mechanical model of the skin interface was constructed using the mechanical theory of the stitched interface, and the mathematical model for predicting the tensile stiffness was obtained. Combined with numerical simulation and physical experiment, the influence of shape factor and tooth tip Angle on the tensile properties of skin suture structure was analyzed, and the influence of tip area proliferation on the tensile properties of interface structure was further explored. The results showed that the zigzag structure had significant tensile stiffness compared with other suture structures, and the stiffness of the four types of suture structures showed a decreasing trend with the increase of the tooth cusp Angle, and the tip area further improved the tensile properties of the suture interface, which could provide relevant references for improving the healing rate of skin wounds after clinical suture.
2024 Vol. 45 (6): 795-807 [
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23
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808
Study on Free Vibration and Bending Deformation of Functional Gradient One-dimensional Hexagonal Quasicrystal Laminated Beam
In this paper, the free vibration and bending problems of one-dimensional(1D) hexagonal quasicrystal(QC) laminated beams with functional gradients are investigated using the pseudo-Stroh formula. The QC laminated simply supported beam is modeled, and the transfer matrix method is used to derive the exact solutions of the natural frequency of free vibration and bending deformation displacement of the beam under the simply supported boundary conditions. The results are compared with the existing ones to verify the accuracy and precision of the model and method. The effects of high span ratio, layer thickness ratio and functional gradient coefficient on the natural frequency and bending deformation of 1D QC laminated simply supported beams under two different stacking sequences are analyzed by numerical examples. The results show that the natural frequency increases with the increase of the functional gradient coefficient, and the phonon displacement decreases while the phason displacement increases with the increase of the functional gradient coefficient under the two stacking sequences. The exact solutions obtained in this paper can provide theoretical references for various numerical methods and experimental results for the study of QC beams.
2024 Vol. 45 (6): 808-819 [
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14
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820
Aerothermoelastic analysis and flutter bound control of composite laminated panels
This paper focus on the aerothermoelastic characteristics of composite laminated panels subjected to supersonic airflow, and implements macro fiber composite (MFC) materials for active flutter bound control. The aerodynamic pressure is calculated by utilizing supersonic piston theory, and the system's motion differential equations are established based on the assumed mode method and Hamilton's principle. The aerothermoelastic characteristics of the structural system are analyzed via the frequency domain method. The research examines the influences of ply angles and geometric parameters of the laminated panels on the variations in critical flutter aerodynamic pressure and critical buckling temperature. The proportional feedback control is designed to compute the flutter bounds under different gain coefficients. The results demonstrate that the laminated panel with ply angle of [90°/?90°/90°] exhibits the poorest aerothermoelastic stability for various aspect ratios. For larger ply angles, an increase in aspect ratio enhances the aerothermoelastic stability of the laminated panels. Moreover, the proportional feedback control method can significantly enhance the system's flutter bound, but the gain coefficients requires to be adjusted to ensure the stability and performance of the control system.
2024 Vol. 45 (6): 820-830 [
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14
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831
Design of Continuously Density-Graded Porous Metal Materials in Polar Coordinates and Study on the Blast Resistance of Sandwich Tubes
In this paper, the dynamic response of continuously density-graded aluminum foam sandwich tubes under internal explosion load was studied. The finite element model of the continuously density-graded aluminum foam and sandwich tubes was established in polar coordinates by 3D-Voronoi technology. The influences of the core density distribution, such as positive-gradient, negative-gradient, and V-shaped gradient including high in middle and low at both ends (middle-high-gradient), low in middle and high at both ends (middle-low-gradient), core density gradient, the assembly method of the tube wall and core, and length-to-diameter ratio of explosives on the antiknock performance of the sandwich tube structure were analyzed. The results demonstrate that when the core density gradient is the same, the maximum deformation of the outer tube in the sandwich tube with a negative-gradient core is the smallest, the sandwich tube with a middle-low-gradient core has the highest specific energy absorption, and the antiknock performance of the sandwich tube with a middle-high-gradient core is the worst. As the 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 of the sandwich tube with a middle-low-gradient core shows a trend of first increasing and then decreasing, while the anti-explosion performance of the sandwich tube with a middle-high-gradient core weakens. The ideal bonding between the 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. Under different length-to-diameter ratio of explosives, the maximum deformation of the outer tube in the sandwich tube with a negative-gradient core is smaller. The present work is expected to provide some insights for researchers and engineers to design such structures for protective engineering applications.
2024 Vol. 45 (6): 831-845 [
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846
Traveling Wave Vibration Characteristics of Hard Coating Damping Double Thin-Walled Cylindrical Shells Coupled Structure with High Rotating Speed
The connection conditions and vibration suppression methods of the shell coupled structure have received much attention. Moreover, the shell coupled structure, as a key component in an aero-engine, should focus on the study of traveling wave vibration characteristics. Therefore, this paper analyzes the traveling wave vibration characteristics of a rotating hard coating damping double thin-walled cylindrical shells coupled structure with bolt connection. Firstly, the discontinuous arc connection is constructed to simulate the actual bolt connection conditions by improving the artificial spring distribution method of the continuous whole circumference. And the artificial spring technique is used to construct the boundary conditions of the shell structure. Secondly, the strain energy of the hard coating shell structure is determined based on Sander’s shell theory. Finally, 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 to solve the calculation, the rationality and accuracy of the theoretical methods are verified by literature and the finite element method. The effects of rotational speed, connection stiffness, hard coating thickness, and boundary conditions on the traveling wave vibration characteristics of the shell structure are also 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 the separation phenomenon and an overall increasing trend in the traveling wave frequency. The effect of the larger hard coating thickness on the traveling wave frequency is more obvious, and the maximum increase in the traveling wave frequency can be up to 5.87% when the hard coating thickness is increased from 0 to 0.85 mm. Overall, the findings of this paper can provide theoretical references and data support for the engineering design of a hard coating double thin-walled cylindrical shells coupled structure.
2024 Vol. 45 (6): 846-856 [
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16
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