Acta Mechanica最新文献

Cross-sectional warping and distortion effects may play a significant role in the axial, bending, and torsional modes of rods, especially for very large deformations. This paper investigates the ability of higher-order beam elements based on the Absolute Nodal Coordinate Formulation (ANCF) to accurately describe the mechanical behavior of solid rods with complex cross-sections, in which the transverse parameters of the position vector are constructed using the Taylor-like polynomials. In order to consider the coupling of deformations, the nonlinear strain–displacement relations are established by the continuum mechanics theory. Furthermore, a numerical quadrature scheme for different cross-section configurations is presented. By comparison to the finite solid element in common software ABAQUS, the results demonstrate that the second-order and fourth-order ANCF beam elements can achieve sufficient accuracy for the rod cross-sectional deformations during the bending and torsion process, respectively. The work provides a basis for element choice in static and dynamic simulations of rod-type structures.

The present study aims to analyze the buckling, free vibration, dynamic instability, and flutter characteristics of innovative variable stiffness composite laminated plates with magneto-electro-elastic (VSCL-MEE) face sheets, utilizing a reliable and validated isogeometric analysis (IGA) framework. On the basis of the generalized higher-order shear deformation theory, Maxwell’s equations, first-order piston theory and magneto-electro-elasticity, the weak form for the governing equations of motion are established according to Hamilton’s principle. The unknown displacements, electric and magnetic potentials are subsequently discretized by IGA approximation, leading to the discretized governing equations of motion for the VSCL-MEE plates. The buckling, free vibration, and flutter behaviors are determined directly by solving the corresponding characteristic equations, while the dynamic instability regions are identified using the Bolotin method. Several benchmark examples on free vibration of MEE plates, dynamic instability of isotropic plates and free vibration of VSCL plates are provided to make sure the correctness of present formulation and computational framework. In numerical investigation, three patterns of stacking sequences of the VSCL core are analyzed that constructed on the basis of the straight fiber configurations of unidirectional, symmetrically balanced and quasi-isotropic laminates. The numerical results demonstrate that the ply orientations, stacking sequence patterns, MEE layer thicknesses, and plate dimensions significantly influence the buckling, free vibration, dynamic instability, and flutter responses of VSCL-MEE plates. In summary, the proposed sandwich structure presents a lightweight, adaptive, and self-aware system, ideally suited for pioneering applications in smart morphing wings, high-speed robotic arms, and intelligent wind turbine blades.

In this study, the size-dependent static tensile and axial vibrational responses of piezoelectric semiconductor nanobars are investigated using strain-driven and stress-driven dual-phase local/nonlocal integral constitutive models. A linearized one-dimensional phenomenological framework for piezoelectric semiconductors is employed to establish the governing equations. The two-phase local/nonlocal integral formulation is implemented, which is subsequently transformed into differential formulations with corresponding constitutive constraints. A few dimensionless variables are introduced to streamline mathematical derivations. The general differential quadrature method is utilized to obtain the numerical solutions. The influence of nonlocal parameters on the static extension displacement, electric potential, and undamped natural frequencies of piezoelectric semiconductor nanobar are investigated under different boundary and loading conditions. Critical comparisons between strain-driven and stress-driven modeling paradigms are highlighted to elucidate their distinct predictive capabilities in nanoscale electromechanical coupling phenomena.

Ultrasound stimulation has emerged as a promising noninvasive approach for vision restoration, yet conventional capacitive micromachined ultrasonic transducers (CMUTs) face limitations such as high actuation voltages and insufficient pressure output. This study introduces an innovative CMUT design incorporating a soft porous graphene-reinforced polydimethylsiloxane (PDMS) gap-filling material to address these challenges. Unlike conventional uniform or non-porous gap materials, the porous graphene-PDMS composite simultaneously enables lower operational voltages with improved sensitivity and mechanical stability. A comprehensive nonlinear electromechanical model, leveraging the physically gradient descent-based learning method, captures the complex coupling between the displacement-dependent dielectric properties and the nonlinear plate dynamics. This integrated approach uniquely predicts enhanced resonance responses and acoustic output, providing valuable insights for designing high-performance CMUTs in biomedical applications. The integration of graphene nanoplatelets improves the dynamic response and reduces actuation voltage, optimizing performance for retinal stimulation. Key results include a 32.7% increase in transversal displacement, a 24.3% reduction in actuation voltage, and a 46.2% enhancement in first harmonic resonance amplitude. The proposed CMUT generates 2.4 times higher acoustic pressure at 2 MHz, with a 100-element array achieving 55 Pascals for photoreceptor stimulation and a 1600-element array producing 35 Pascals for ganglion and bipolar cells. These findings highlight the potential of porous graphene-reinforced PDMS to advance CMUT-based retinal prosthetics, offering improved efficiency, safety, and precision for noninvasive therapeutic applications.

This paper investigates the nonlinear free vibration of functionally graded porous graphene platelets-reinforced composite (FGP-GPLs) plates resting on the Kerr foundation, with piezoelectric sheets integrated on the upper and lower surfaces. The material model of the composite layer incorporates three types of porosity and three distinct patterns of graphene platelets distribution. To determine the effective material properties of the composite layer, the Halpin–Tsai micromechanical model, the rule of mixture, and the closed-cell Gaussian random field scheme are employed. The numerical model of the piezoelectric smart laminated structure is developed, carefully considering the effects of the piezoelectricity and flexoelectricity, temperature, and von Kármán nonlinear assumption. This is done in conjunction with the higher-order shear deformation theory (HSDT), the modified couple stress theory (MCST), and isogeometric analysis (IGA) techniques. The nonlinear response of the numerical model is solved using a direct iterative method. The accuracy and effectiveness of the model and solution approach have been validated through comparison with results from the available literature. Lastly, a comprehensive discussion is provided on the effects of various parameters, including the distribution patterns of porosity and graphene platelets, the porosity coefficient, the weight fraction of graphene platelets, the temperature rise, the stiffness of the elastic foundation, the flexoelectric effect, and the size-dependent effect on the nonlinear free vibration of the piezoelectric functionally graded porous graphene platelets-reinforced laminated plate resting on the foundation.

Graphene-reinforced composites are increasingly employed as core layers in smart microplates due to their exceptional mechanical and functional properties. Although graphene or graphene platelets (GPLs) are typically used to reinforce homogeneous matrices, integrating GPLs into conventional functionally graded materials (FGMs) represents a novel approach. This study proposed a new material model comprising a GPL-reinforced FGM core with piezoelectric coating layers. The composite matrix is continuously graded through the thickness following a power-law distribution, and five distinct GPL dispersion patterns are examined. The core’s material properties are determined using the modified Halpin–Tsai model in conjunction with the rule of mixtures. Based on variants of a four-unknown refined plate theory (RPT4) combined with the modified couple stress theory (MCST), governing equations for smart GPL-reinforced FGM microplates with two piezoelectric layers resting on a Winkler–Pasternak foundation are derived. A Navier-based analytical solution is then employed to compute the natural frequencies of the piezoelectric microplate. The performance of the proposed model and the different RPT4 variants is assessed, and the influences of material parameters, piezoelectric layer thickness, length scale, and foundation parameters on the natural frequency are thoroughly investigated.

A geometrically nonlinear framework is constructed for modeling material failure by adiabatic shear. Mechanisms encompassed include nonlinear thermoelasticity pertinent for high-pressure and high-temperature states, dynamic plasticity from combined actions of dislocation glide and twinning, initial and evolving porosity, rotational dynamic recrystallization (DRX), and localized material degradation from softening and ductile fracture. An order parameter of phase-field type accounts for softening mechanisms at a microstructure length scale too small to be resolved in structural mechanics applications. Phase-field regularization sets the finite width of a shear band or ductile crack, analogous to application of phase-field theory for regularizing sharp cracks in brittle fracture. The framework depicts the reduction in resistance to shear banding with (initial) defects or pores, and DRX, in a physically motivated scheme different from prior theory. Model calculations reproduce experimental observations on shear localization and fracture in steel and titanium, the latter with and without initial pores and DRX, under dynamic shear-dominant loading. Further results predict decreased shear stability from void growth under tensile pressure. Compressive pressure increases flow strength, leading to higher temperature and earlier localization in some cases, but later localization in others due to suppressed thermoelastic expansion. Higher loading rates can increase stability due to rate dependence of flow stress, transient phase-field kinetics, and possible inertial effects.

This research focuses on developing a numerical model for predicting time-varying displacement responses of damaged fibre-metal laminate (FML) hybrid structural components using a higher-order mathematical model, including pre-damage. The numerical solution accuracy obtained using a customized computational code (MATLAB) through the mathematical model is verified with experimental dynamic deflection data. The numerical transient responses are computed through Newmark’s (average acceleration) integration technique in association with the isoparametric finite element approach. Additionally, the pre-damage (crack) is introduced through a variable crack closure technique (VCCT) in a simulation tool (ABAQUS), and the mesh details, including the nodal information, are imported to the MATLAB platform using the compatibility code. For experimental validation purposes, a few hybrid FML (glass fibre epoxy panels joined with aluminium plates) are fabricated and utilized for experimentation, including the experimental material properties. The numerical model accuracies are initially verified with previously published transient values of the laminated composite. After fulfilling the necessary convergence criteria and the validation, the computational model is extended to work out a few parametric analyses to understand the significance of damage and limiting factors (curvature ratio, geometric shapes, and modular ratios) in designing such FML components. It can be concluded from the numerical experimentation that the geometrical parameters (curvature ratio, stacking sequence, and aspect ratio) largely influence the dynamic deflections, i.e. the responses vary from 4–8% (increase in peak displacement). Meanwhile, the values upsurge by 32%, while the structural end-restrained conditions are less (for a cantilever case: CFFF). Finally, a set of recommendations is listed to understand the advantages of the proposed model for the analysis of FML structure, including the damage effects.

Considering the increasing demand for vibration and noise control in fluid-conveying pipeline systems, this study presents the wave-based analytical model for investigating the vibration behavior of periodic pipe structures filled with internal fluids. The model is formulated by integrating Timoshenko beam theory with the wave-based method. Governing differential equations are derived, considering both cross-sectional deformation and shear effects. A fluctuation-type solution is employed to obtain the displacement fields. Based on the displacement and force continuity conditions at the interfaces of adjacent units, together with the appropriate boundary conditions, the global dynamic equations of the periodic fluid-filled pipe structure are derived.The model’s accuracy is validated through comparison with finite element method (FEM) results. Subsequently, a parametric analysis is performed to examine the effects of fluid velocity, structural geometry, and material properties on the bandgap characteristics. The proposed framework offers theoretical insights and practical guidance for the design and vibration control of fluid-filled periodic pipeline systems.