To evaluate the influence of sectional seam configurations (normal vs. oblique) on the fault-crossing performance of tunnels, this study integrates 1:40 scale model tests with three-dimensional elasto-plastic finite element simulations. The mechanical behavior and damage mechanisms of tunnels subjected to normal fault dislocation were comprehensively examined through deformation patterns, contact earth pressure, strain distribution, internal force characteristics, and failure modes. Experimental results indicate that tunnels with normal seams undergo severe longitudinal tensile-flexural failure and shear-induced spalling near the fault rupture surface, accompanied by dense cracking. In contrast, oblique seam tunnels demonstrate enhanced structural flexibility, reduced crack density, and absence of large-scale spalling, reflecting improved adaptability to fault displacement. Peak longitudinal strain was reduced by up to 80

Surface modification is one of the effective methods to improve the stability of electrical contact. In this study, laser shock peening (LSP) was applied to pure copper, and subsequent changes in morphology, hardness, microstructure, residual stress, and fretting wear behaviors were analyzed. The relationship between debris behavior and electrical contact resistance (ECR) was examined using ECR instantaneous values against displacement (R-D curves). LSP increased surface hardness by 26

Piezoelectric semiconductor (PSC) materials exhibit strong electromechanical coupling affected by free carriers, which makes their contact behavior essential for sensors, actuators, and electronic devices. Analytical models for three-dimensional (3D) PSC contact problems are still scarce, especially for conductive indenters. This work develops a semi-analytical framework to study the 3D frictionless contact between a conductive indenter and a PSC half-space. Fundamental solutions under a unit force and a unit electric charge are derived, and the corresponding frequency response functions achieve an efficient semi-analytical contact model. The numerical results demonstrate that an increase in the surface charge density reduces the indentation pressure and modifies the electric potential distribution. A higher steady carrier concentration enhances the screening effect, suppresses the electromechanical coupling, and shifts the system response toward purely elastic behaviors. The sensitivity analysis shows that the indentation depth is dominated by the elastic constants, while the electric potential is mainly affected by the piezoelectric coefficient. Although the analysis is carried out with spherical indenters, the model is not limited to a specific indenter shape. It provides an effective tool for investigating complex 3D PSC contact problems and offers useful insights into the design of PSC materials-based devices.

This study thoroughly examines and compares the wind-induced forces and flutter behaviors of rectangular sections with B/H = 5 and 10 (where B and H denote, respectively, the width and height) over various vibration amplitudes, utilizing single-degree-of-freedom (SDOF) vertical/torsional forced vibration wind tunnel tests and theoretical analysis. The involvement of various components of wind-induced forces with respect to vibration amplitude and reduced wind speed was analyzed. The results reveal a pronounced competitive interplay between vortex-induced and self-excited forces for the rectangular section with B/H = 5. A comprehensive comparison is conducted on the fundamental harmonic components of self-excited forces for both sections, including the magnitude and phase characteristics of the aerodynamic coefficients, as well as the three-dimensional evolution of flutter derivatives with respect to wind speed and amplitude. The findings highlight the remarkable sensitivity of the aerodynamic parameters of the B/H = 5 rectangular section to the regular vortex shedding. Furthermore, a qualitative elucidation of the flutter mechanism of an SDOF torsional conservative system is conducted, identifying the intrinsic and decisive role of the phase difference between torsional motion and the self-excited-moment in governing post-critical aeroelastic behavior of the two sections. Finally, a quantitative comparison of the vertical-torsional coupled flutter is performed, with particular attention to the stability of limit cycle oscillations (LCOs), the flutter essence, coupling effects, and the amplitude-dependent aerodynamic damping mechanisms underlying post-flutter responses.

Interface defects or weak bondings often induce the degradation of multiphysics coupling properties in intelligent magnetoelectric structures during operational contact situations. This study develops a computational model combining the hybrid element method to solve transient contact responses of the polymer-based magnetoelectric coating imperfectly bonded to a magneto-electro-elastic substrate with efficiency. The interfacial discontinuity of mechanical and electromagnetic fields is characterized by five imperfection indices, quantifying the discontinuous transfer of the displacement, electric potential, and magnetic potential across the coating–substrate interface. Time-dependent relaxation functions are employed to derive viscoelastic frequency response functions by replacing the corresponding elastic Green’s function based on the elastic–viscoelastic correspondence principle. Parametric analyses are conducted to investigate the effect of the film thickness, friction coefficient, action time, and imperfection index. Numerical simulations under five distinct interfacial conditions show that interfacial imperfections can lead to stress redistribution or concentration, enhance the viscoelastic friction, and modulate magnetoelectric coupling. This study can provide a theoretical basis for structural reliability and performance optimization.

This study develops a frictionless thermoelectro-mechanical adhesive contact model for a rigid spherical indenter interacting with a thermoelectric thin film bonded to a rigid substrate. Thermoelectric and elastic frequency–response functions are derived from the coupled constitutive equations and boundary conditions using a double Fourier transform. The resulting semi-analytical solution is evaluated with a discrete convolution and fast Fourier transform (DC–FFT) formulation combined with a conjugate gradient method (CGM) for the Maugis–Dugdale cohesive conditions. The calculations show that energy increases the central contact pressure through constrained thermal expansion, whereas electric current produces the opposite trend under the prescribed loading convention. Adhesion strength increases the contact radius and shifts the unloading limit point toward a more negative normal load, while film thickness controls the effective compliance by changing the substrate constraint. These results demonstrate that energy, electric current, film thickness, and adhesion strength provide independent parameters for tuning the pressure, deformation, cohesive zone response, and separation stability of thermoelectric thin-film interfaces.

A three-dimensional size-dependent elastodynamic contact model is established and the steady-state contact responses of a microball moving at high speed on the surface of an elastic half-space are investigated. The semi-analytical contact model is developed based on the frequency response functions and the discrete convolution-fast Fourier transform algorithm, in which the frequency response functions are derived within the framework of couple stress elastodynamics. The proposed model can be used to predict the micro scale-induced stiffening and speed-induced softening on contact behavior during steady-state high-speed relative motion of contacting bodies. Detailed parametric analysis of the steady-state elastodynamic contact problem of microball is conducted based on this semi-analytical model. The influences of the characteristic material length, the speed ratio, and Poisson's ratio on contact responses are presented. The results indicate that when the relative speed exceeds 0.2 times the shear wave speed, using a quasi-static model, which neglects elastodynamic effects, to predict contact responses will result in non-negligible errors.

Given the pronounced aerodynamic nonlinearities and site-specific wind turbulence affecting certain long-span bridges characterized by bluff body main girders, this study investigated the aeroelastic response of a two-degree-of-freedom (2DOF) bridge system incorporating both buffeting forces (BFs) and nonlinear aerodynamic effects using a proposed hybrid time-domain analysis method. The results showed that the inclusion of BFs significantly weaked the aerodynamic stability of the self-excited system, leading to a substantial increase in the peak response. The hardening non-Gaussian characteristics of the responses were characterized, and the contributions of the self-excited vibration component (SEVC) and the forced vibration component (FVC) to the response were quantified. Through an energy exchange behavior analysis, the underlying mechanisms by which the BFs influence the SEVC and the subcritical Hopf bifurcation of the self-excited system were explored. The results indicated that SEVC accounts for most of the large-amplitude vibration, with FVC serving as the perturbation that initiates the vibration. However, FVC is indispensable for the large-amplitude oscillations when the wind speed approaches or lies within the subcritical Hopf bifurcation regime. This is attributed to weak modal damping, caused by the antagonistic interplay between self-excited forces (SEFs) and structural damping.

Replacing the conventional sliding strip with a rotatable roller, i.e., substituting two-dimensional sliding contact with rolling-sliding contact, is expected to significantly reduce the wear of the pantograph-catenary tribopair. Herein, the evolution mechanism of current-carrying rolling-sliding friction with varying current and normal force, the coupled effects of current-induced thermal loading and mechanical deformation on microstructural evolution, and comparative analysis in rolling-sliding contact, pure sliding contact, and pure rolling contact were investigated by analyzing the electrical contact resistance (ECR), coefficient of friction (COF), and the evolution of surface and subsurface damage. The ECR exhibited four stages: initial ascending stage, descending stage, steady stage, and re-ascending stage, which corresponded to the initial, ascending, and steady stages of the COF. As the current increased, the primary damage mechanisms comprised delamination, oxidative wear, and arc erosion, indicating a combination of mechanical and electrical wear. This combined regime shifted toward predominantly mechanical wear under higher normal force. The coupled action of high normal force and current led to the coexistence of grain refinement and recrystallization. The nanohardness decreased following the order of 50 N and 20 A (2.54 MPa), 200 N and 20 A (2.07 MPa), 50 N and 0 A (1.84 MPa). The current-carrying rollingsliding contact had the lowest wear depth of 3.6 mu m, whereas the pure sliding contact had a wear depth of up to 1870 mu m. The findings provide fundamental insights for the design of an advanced electrical contact tribopair.

This study presents a multimode coupled nonlinear flutter approach in terms of the rational function (RF) approximation technique and amplitude-dependent flutter derivatives, to address the underdevelopment of three-dimensional (3D) nonlinear flutter analysis for long-span suspension bridges. A high-order RF is invoked to characterize the 3D inhomogeneous distributed nonlinear self-excited forces resulting from spanwise variated flutter derivatives and multi-mode coupling. An iterative approach is utilized to determine the spanwise amplitude distributions under specific cycle steps, while a matrix optimization procedure is introduced to least squares identifying the coefficient set of the RF relevant to 3D aerodynamics. The frequency-independent complex eigenvalue method combined with cycle calculations is used to determine the 3D distributed modal characteristics as functions of wind speed and amplitude. By utilizing the existing double-layer iterative method along with a numerical example, the precision and robustness of the proposed method are validated from various perspectives, including flutter response, modal characteristics, spanwise limit cycle oscillation amplitude, and 3D nonlinear vibration characteristics. In conclusion, the method demonstrates good precision, robustness, and the ability to automatically search for multi-mode coupling characteristics and shows fewer limitations on the number of modes.

Polymer-based magnetoelectric materials, a type of three-phase polymer matrix smart composites, have emerged as a promising solution for enabling smart structural systems with advanced functionalities and demonstrating great potential for practical engineering applications. These smart composites come into contact with different rigid engineering components with the time-dependent multiphysics response. This study reports a novel hybrid element model for addressing the three-dimensional frictional sliding contact problem between a rigid spherical punch and such materials, in which the electro-magneto-viscoelastic behavior induced by the polymer matrix, piezoelectric phases, magnetostrictive phases are taken into account. Frequency response functions for unit electric, magnetic, and mechanical loads are derived based on the elastic–viscoelastic correspondence principle. During the transient regime analysis, the contact pressure, in-plane stress, and electric/magnetic potentials are numerically computed using the conjugate gradient method and discrete convolution-fast Fourier transform. The study delves into the combined effect of the surface electric/magnetic charge density and friction coefficient on the time-dependent contact behavior.

In this study, the dispersion behavior of piezoelectric sandwich nanoplates is examined using the nonlocal strain gradient theory (NSGT). Specifically, the evolution law of frequency and phase velocity (PV) with the wave number (WN) is investigated. The sandwich nanoplate has a metallic central layer and a piezoelectric surface layer, and the nanoplate is deposited on top of a viscoelastic substrate. The viscoelastic substrate is modeled using a three-parameter viscoelastic model. The surface effects (SEs) of the piezoelectric layer, including its elastic parameters, piezoelectric parameters, dielectric parameters, and residual stresses, on the dispersion characteristics are systematically considered. The equations of motion are determined by Hamilton's principle and NSGT. Furthermore, the scale effects, SEs, and viscoelastic effects on the dispersion properties are comprehensively explored. The results reveal that the contribution of scale and viscoelastic effects to the dispersion properties is strongly dependent on the WN, and the impact of SEs on the frequency is inseparable from the thickness of the piezoelectric sandwich nanoplates.

The tunnel portal, influenced by the slope geometry and the fractured surrounding rock, constitutes a vulnerable point in terms of seismic resistance. To investigate its dynamic response under SV waves, we derive the displacement wave field for a single-sided slope subjected to SV wave incidence, based on the principles of wave dynamics and Ray theory. An elastic foundation beam model for the tunnel portal is developed, accounting for the interaction between the tunnel and the surrounding rock. Analytical expressions for the hoop and longitudinal strains are derived, and the effects of the slope angle, seismic wavelength, frequency, and elastic foundation modulus are examined. By analyzing the distribution of strain extrema under vertically incident SV waves, we identify the seismic weak points of the tunnel portal. Key findings include the following: under SV wave incidence, the hoop strain response at the crown and inverted arch is significantly higher than at the spandrel, foot, and waist, with the crown and inverted arch identified as the seismic weak points. In contrast to SH waves, SV waves cause a shift in the strain peak due to wave transformation, leading to variations in the damage locations along the tunnel's longitudinal axis. The strain distribution at the tunnel portal exhibits a bimodal characteristic, and the seismic reinforcement zoning for the portal section under vertically incident SH waves remains valid.

Segmental linings can effectively mitigate tunnel damage caused by normal fault dislocation. To improve the tunnel's resistance to normal fault displacement, the fault resistance performance of segmental linings composed of conventional reinforced concrete segments and basalt fiber-filled concrete segments was investigated. A numerical model of the tunnel-surrounding rock system was established and verified for predicting deformation and damage evolution. Nine orthogonal experiments yielded a comprehensive six-indicator evaluation system for quantitatively assessing tunnel failure. Range analysis methodology was employed to quantify parameter sensitivity through calculation of damage index ranges across parameter levels. This systematically ranked the relative influence of: conventional segment length (6m, 9m, 12m), basalt fiber-filled segment length (0.4m, 0.6m 0.8m), and basalt fiber volume content (0.5 %, 0.4 %, 0.3 %) on the tunnel fault resistance. The results show that fiber-filled segmental linings perform well in most indicators. Shorter conventional reinforced concrete segmental length reduces plastic damage and enhance the tunnel's fault dislocation resistance. Basalt fiber-filled concrete accommodates larger fault displacements, reduces lining damage, and lowers the load utilization ratio. Increasing the fiber-filled segmental length reduces lining damage while decreasing the load utilization ratio, whereas narrowing it confines fault influence; thus, an optimal length balances these effects and modulates the load utilization ratio.

Tunnel portals are particularly vulnerable during seismic events due to the influence of adjacent slope geometry and fractured rock formations. This study evaluates the seismic response of tunnel portals and determines an appropriate fortification range. Ray theory is employed to calculate the displacement field of a single-sided slope subjected to incident SH waves, while the tunnel entrance is modeled as an elastic foundation beam. An analytical expression for hoop strain is derived, accounting for the interaction between the tunnel and the surrounding rock, as well as the attenuation of seismic waves. A parametric analysis is also performed to examine the impact of slope angle, seismic wavelength, frequency, and foundation stiffness on the tunnel response. Shaking table tests are conducted to validate the theoretical results and reveal failure patterns in both the slope and tunnel. The findings show that the spandrel and arch foot exhibit the highest hoop strain responses, identifying these positions as critical points of seismic vulnerability. The seismic-affected zones of the tunnel portal are classified into three distinct regions based on the distribution of peak hoop strain. The recommended fortification range for the tunnel portal extends up to 7.5 times the tunnel span, effectively encompassing the areas of peak strain to mitigate potential damage.

A rigid-flexible coupling dynamics model was developed to investigate the vibration characteristics of rotating functionally graded (FG) imperfect microplates subjected to in-plane loads. The displacement field and constitutive relationships were derived based on a four-variable refined plate theory and the modified couple stress theory. A novel C1-type nine-node, 100-degree-of-freedom differential quadrature finite element (DQFE) was constructed by applying the differential quadrature and Gauss-Lobatto quadrature rules to discretize the variable-coefficient model. The vibration equations were derived using the Euler-Lagrange formulation and solved through complex modal analysis. The numerical results were validated for convergence and accuracy. A comprehensive analysis of the effects of geometric imperfections, rotational speed, material length scale parameter (MLSP), and in-plane loads, as well as their combined influence, on the vibration behavior was conducted. The results show that the amplitude of geometric imperfections, rotational speed, and MLSP jointly affect the regions of frequency locus veering and modal transitions. The modal assurance criterion (MAC) matrix was used to quantitatively assess the impact of these parameters on vibration modes. Global imperfections were found to have a more significant influence on frequencies than local imperfections. Moreover, the distribution type and direction of in-plane loads were shown to affect frequencies differently for various vibration modes. This study offers valuable theoretical insights for damage detection, modal analysis, and fault assessment in rotating plate structure across different scales.

This paper introduces an innovative contact model utilizing the hybrid element method to investigate the three-dimensional time-dependent contact problem of a rigid spherical punch sliding on magnetoelectric polymer matrix composite films. Frequency response functions are derived by replacing the corresponding elastic Green’s function with time-dependent relaxation functions via the elastic/viscoelastic correspondence. Highly efficient iterative solutions of the transient contact response are realized by using the conjugate gradient method and discrete convolution-fast Fourier transform algorithm. The present model is verified by comparisons with the literature. Parametric analysis is performed to investigate the influence of the sliding velocity, film thickness, contact time, and friction coefficient on interaction mechanisms by analyzing transient contact behaviors of the material. The proposed contact model provides a theoretical foundation for the thickness optimization, friction control, and electromagnetic output stability of magnetoelectric composite films.

This paper proposes a semi-analytical numerical method for size-dependent three-dimensional adhesive contact problems applicable to various surface geometries. The model is developed based on frequency response functions within the couple stress elasticity framework and an adhesion-extended conjugate gradient method, and employs the Maugis-Dugdale adhesion model to characterize interfacial adhesion behavior. The proposed approach provides a general tool for investigating the adhesive contact behavior of dissimilar elastic materials under the influence of size effects. A detailed parametric analysis is performed using this model to assess the influence of the shear modulus ratio, adhesion parameter, characteristic material length, and normal force on key adhesive contact responses, including pull-off force, contact radius, attraction force, contact pressure, and normal displacement. Results demonstrate that the shear modulus ratio plays a pivotal role in governing adhesive contact behavior in the case of size effects that cannot be neglected. The developed semi-analytical numerical model offers important insights into the adhesive contact mechanics of complex microstructures.

This paper reports a novel model for solving size-dependent three-dimensional thermoelastic contact behavior. The model accounts for the effects of local bending in microstructured materials and the interface heat flux on size-dependent thermoelastic contact behavior. Analytical expressions for the material response under unit heat flux and unit force have been derived within the framework of higher-order thermoelastic continuum theory. A semi-analytical contact model is established based on the conjugate gradient method and discrete convolution fast Fourier transform, which incorporates thermo-mechanical coupling effects at the contact interface and has no restrictions on the geometry of the contact surfaces. Based on the developed model, detailed parametric analyses have been conducted with two typical indenter shapes, spherical indenter and flat-ended cylindrical indenter, to discuss the combined effects of thermal expansion, size dependence, and material properties on microscale thermoelastic contact behavior.

This study examines the aerodynamic forces on an oscillating 5:1 rectangular cylinder in smooth and turbulent flow by single-degree-of-freedom (SDOF) vertical/torsional forced vibration wind tunnel tests. It quantifies the energy contributions of different components of aerodynamic forces with respect to reduced wind speed and amplitude. The critical role of turbulence in suppressing regular vortex shedding is highlighted, along with its modifying effect on fluid memory effects and aerodynamic force coefficients. The decisive role of the phase difference between self-excited-moment and torsional motion on the aeroelastic stability of an SDOF torsional conservative system is revealed. The amplitude-dependent flutter derivatives were extracted, showing significant turbulence effects and thereby notable changes in the transmission between fluid and self-excited forces. The aeroelastic response of a vertical-torsional coupled system was analyzed, revealing that turbulence-induced variations in aeroelastic stability are primarily due to changes in uncoupled aerodynamic damping. Compared to a smooth flow, the system exhibits an enhanced aeroelastic stability and smaller stable limit cycle oscillation (LCO) amplitudes within a certain wind speed range under turbulent flows. However, at high wind speeds, the response transitions to hard flutter, whereas in a smooth flow field, it generally manifests as soft flutter with stable LCO.