The pseudo-Stroh formulism can transform the governing equations of multi-field coupling materials such as quasicrystals into a linear eigensystem, enabling the exact solution of multilayered structures with simply-supported boundary conditions. This provides an important reference for various numerical and experimental methods of quasicrystal beams in engineering practice. 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. A simply-supported QC laminated beam is modeled, and the transfer matrix method is used to derive the exact solutions for natural frequency of free vibration and bending deformation displacements of the beam under simply-supported boundary conditions. The obtained results are compared with the existing ones to verify the accuracy and precision of the presented model. Numerical examples are provided to show the effects of high span ratio, layer thickness ratio, and functional gradient coefficient on the natural frequency, bending deformation, and mode shape of simply-supported 1D QC laminated beams under two different stacking sequences. The results show that natural frequency increases with the increase of functional gradient coefficient. Phonon displacement decreases while phason displacement increases with the increase of functional gradient coefficient under the two stacking sequences. Functional gradient coefficient and stacking sequence minimally affect phonon displacement modes but significantly impact phason displacement modes. Moreover, they notably affect phason stresses compared to phonon stresses in QC laminated beams. Thus, the optimal natural frequency and deformation displacement of a QC beam can be achieved by adjusting geometric size, stacking sequence, and functional gradient coefficient of the layered beam. These findings can provide theoretical references for various numerical methods and experimental studies on QC beams.

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.

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.

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.

To improve blast and impact resistance of sandwich structures, this study introduces a composite sandwich structure comprising a re-entrant (RE) negative Poisson's ratio core, polyethylene (PE) fibers, and silicon carbide (SiC) ceramics. Utilizing the coupled Eulerian-Lagrangian (CEL) algorithm within ABAQUS, the dynamic response of this structure under explosive loading was simulated, assessing the impact of various core layer configurations on protective performance through structural deformation mechanisms, velocity response features, and energy absorption capacities. At equivalent areal densities, the incorporation of ceramic and polyethylene layers led to reductions in upper and lower panel deformations by up to 53% and 5.7%, respectively, relative to an RE-only sandwich layer. Notably, a core configuration of SiC-PE-RE optimized interlaminar load distribution, minimizing lower panel deformation; an increase in panel support strength correspondingly reduced panel velocities. Positioning the SiC and PE layers at the upper and middle core layers, respectively, achieved peak reductions in upper and lower panel deformations by 18.84% and 16%, compared to the RE sandwich layer, exhibiting the most rapid rate of decay. Conversely, positioning the RE layer at the upper core resulted in augmented local deformations, leading to localized crushing failures in the PE and SiC layers, thereby maximizing the energy-absorption incrementby up to 14%.

To investigate the impact of surface topography on the mechanical properties of additive manufacturing materials, in this paper, high-strength aluminum alloy specimens were fabricated by the selective laser melting method. The influences of scanning speed, heat treatment, deposition direction, and surface roughness on tensile mechanical properties were examined. The surface topography measured by an optical microscope was reconstructed based on the Fourier series and MATLAB software, and the analytical solution of the stress concentration coefficient of the surface topography was derived using the Airy stress function. Finite element analysis was conducted using ABAQUS software to validate the analytical results. The probability density function of the stress concentration coefficient was obtained through normal fitting, and a method for evaluating the reliability of the material based on yield strength was proposed. The proposed methodology in this paper is of reference significance for the quantification of surface roughness and its effect on yield strength of other additive manufacturing materials and specimens.

Conductive polymer composite (CPC) foam exhibits excellent characteristics such as high plasticity, energy absorption, as well as thermal and acoustic insulation, and holds enormous potential for applications in various fields including construction, transportation, electronics, etc. However, the porous structure of CPC foam is usually simple and random, which limits its further application. The complexity of CPC processing makes it challenging to achieve a controlled design of micro-porous structures. Inspired by the idea that biomaterials can enhance their mechanical properties by virtue of their well-aligned anisotropic microstructures, highly aligned anisotropic porous biomimetic microstructures are constructed by a bidirectional freeze-casting process to enhance the compressive mechanical properties of CPC foam. Compared to traditional unidirectional freezing, the compressive elastic modulus and peak stress of aligned anisotropic porous microstructured CPC foam increase by 18.7% and 25.4%, respectively. Buckling and collapsing risks during cyclic compression are significantly reduced, and a peak stress of 91.1% and a strain recovery of 89.6% are still maintained after 2,000 cycles at 50% strain. A finite element model of the porous structure in CPC foam is built with parameters including elastic modulus, hole wall thickness, and Poisson's ratio, obtained from measured data or literature. The quasi-static compressive behaviors of biomimetic and disordered structures are investigated using the finite element method, and the deformation and stress distribution are compared with the corresponding experimental results. Through finite element simulations and experimental tests, it is found that the main mechanisms enhancing the compressive mechanical properties of the materials are as follows: stress distribution optimization effectively prevents plastic deformation caused by local stress concentration; the highly elastic behavior of micrometer pore wall and its 3D structure enhance the bionic structure's resilience; and the highly aligned anisotropic channels provide ample deformation space, improve deformation coordination, and enhance the structure's reversibility during loading and unloading.

Contact resonance atomic force microscopy (CR-AFM) is a powerful technique that enables the measurement of topography and the mechanical properties of various materials at the micro/nanoscale. It can be used in both air and liquid environments. However, when CR-AFM is operated in a liquid environment, the dynamic behaviors of the microcantilever can be significantly different from those in air or vacuum due to the complex fluid-solid coupling of the microcantilever-liquid-sample system and the tip-sample interaction. In this study, we explore the effects of liquid density and viscosity, as well as tip-sample normalized contact stiffness and contact damping, on the dynamics of the AFM microcantilever in liquid environments. We treat the influence of the liquid on the dynamics of the AFM microcantilever as added mass and added damping. Our results show that in free vibration, the natural frequencies of the AFM microcantilever are primarily dominated by the liquid density, while the liquid viscosity plays a dominant role in the quality factor compared to the liquid density. Higher modes exhibit higher sensitivity to changes in liquid viscosity and liquid density. As the normalized tip-sample contact stiffness increases, a higher mode shows increased sensitivity to changes in normalized contact stiffness in a liquid environment. On the other hand, a lower mode is more sensitive to changes in normalized contact damping in a liquid environment. In addition, the dynamic responses of the AFM microcantilever under three different excitation approaches are compared and discussed. Variations in boundary conditions and hydrodynamic loads applied to the microcantilever under these approaches lead to diverse dynamic responses. The findings in this study are essential for the development of micro/nanoscale mechanical property imaging techniques using CR-AFM in liquid environments, as well as the improvement of measurement accuracy and sensitivity.

The material properties of quasicrystals are significantly affected by defects due to high brittleness. Understanding the fracture behavior of quasicrystals is crucial for material applications. In this paper, the fracture mechanics of one-dimensional hexagonal quasicrystals with periodic Type-III multiple cracks emanating from a nanoscale hole is investigated theoretically. Based on complex elasticity theory and the Gurtin-Murdoch surface elasticity theory, stress fields of a nano-hole with periodic multiple cracks, considering surface effects, are obtained using boundary value problems of analytic function theory and the conformal transformation technique. Analytical expressions for stress intensity factors and energy release rates of the phonon field and phase field at the crack tip under the same conditions are further derived. The effects of aperture size, number of periodic cracks, crack-length/aperture ratio, coupling coefficient between phonon field and phase field, and applied loads on dimensionless stress intensity factors and dimensionless energy release rate are discussed. Results indicate that the coupling coefficient, applied loads, and aperture size do not affect dimensionless stress intensity factors without surface effects. Larger aperture sizes show stronger size dependence on dimensionless stress intensity factors and dimensionless energy release rate when considering surface effects. An obvious coupling effect between the phonon field and the phase field is observed. The influence of the number of periodic cracks on dimensionless stress intensity factors and energy release rate is restricted by defect size. The effects of phonon field loads and phase field loads on dimensionless stress intensity factors and energy release rate differ. This work reveals the specific influence of surface effects on the fracture behavior of multi-cracks at the hole edge, offering significant academic insights into quasicrystal fracture mechanics.

Random defects due to differences in raw materials and the complexity of the manufacturing process are inevitable in engineering structures. Based on the inherent characteristics of sensitivity to defects in the film-substrate system, the Monte Carlo method is applied in the study of the stability of structures with random defects, coupled with numerical simulations to investigate the morphological evolution and post-buckling equilibrium path of film-substrate systems with random defects during instability. The numerical results show that the critical load of the structure with random defects is unstable. The defects significantly reduce the critical load of the structure, and the random defects destroy the symmetry of the structure, leading to a transformation from an ordered checkerboard pattern to a disordered fold nuclear pattern, hence affecting the subsequent morphological trend. This analysis assesses the potential risks and effects of random defects in thin-film structures, aiming to improve the reliability and performance of thin-film devices, coatings and surface treatments, and to bridge the gap between theoretical stability research findings and practical design applications.