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Thermo-electromechanical coupling analysis at micro and nano temporal and spatial scales becomes significantly important with extensive application of ultrafast heating technology to micro/nano-machining and manufacturing of piezoelectric micro/nano-devices, where the size effects in heat conduction and elastic deformation remarkably increase. This article aims to establish a new nonlocal piezoelectric thermoelasticity theory based on newly developed model of Eringen-type nonlocal single-phase-lag heat conduction via Eringen's nonlocal continuum mechanics. The proposed model is applied to analyze the thermo-electromechanical responses of piezoelectric nanorod by Laplace transformation technique. The effects of nonlocal characteristic lengths on wave propagations and structural transient response are evaluated and discussed. [ABSTRACT FROM AUTHOR]

The extraordinary properties of graphene nanoplatelets (GPLs) have attracted great attention in the thermomechanical behaviors. Additionally, thermoelastic damping (TED), as a dominant intrinsic dissipation mechanism, is a major challenge in optimizing high-performance micro/nano-resonators. However, the classical TED models fail to explain the thermomechanical behavior considering the influences of the small-scale effect and the memory-dependent effect. To fill these gaps, the present study aims to investigate TED analysis of functionally graded (FG) microplate resonators reinforced with GPLs in the frame of the modified strain gradient theory and the fractional dual-phase-lag heat conduction model. Four patterns of GPLs distribution namely the UD, FG-O, FG-X, and FG-A pattern distributions are taken into account, and the effective material properties of the plate-type nanocomposite are evaluated based on the Halpin–Tsai model. The energy equation and the motion equation in the Kirchhoff microplate model are solved, and then, the closed-form analytical expression of TED is obtained by complex frequency technique. A detailed parametric study has been conducted to discuss the influence of the material length-scale parameter, the fractional-order parameter, and the total weight fraction of GPLs on the TED. The results demonstrated that the energy dissipation of FG microplate resonators reinforced with GPLs is determined by the small-scale effect, the memory-dependent effect, and the total weight fraction of GPLs. This article provides a theoretical approach to predict TED in the design of FG microplate resonators reinforced with GPLs with high performance. [ABSTRACT FROM AUTHOR]

In recent years, the application of porous materials in practical engineering has become increasingly common. Under extreme thermal conditions, how to accurately describe the heat conduction and structural response of porous materials is a key issue in the structural safety and functional design of porous materials. Among them, it is particularly important to consider the size-dependent and memory-dependent effects for small-sized structures or microdevices of porous materials. To address these issues of porous structures and to guide their applications as well as optimization, this paper first investigates the thermoelastic transient response of porous microplates subjected to thermal and stress shocks at the left boundary based on the Atangana-Baleanu (AB) fractional-order generalized thermoelastic theory by considering nonlocal effects and fractional-order strain, which is combined with the thermoelasticity theory of porous materials and the dual-phase-lag (DPL) heat conduction model. The governing equations are then established and solved using the Laplace transform and its numerical inversion. Finally, the effects of newly defined fractional order parameters, nonlocal parameters and the initial magnitude of the mechanical shock on the dimensionless temperature, volume fraction field, displacement and stress distribution are discussed and displayed graphically. [ABSTRACT FROM AUTHOR]

Piezoelectric material structures with an excellent mechatronic coupling property effectively promote self-power energy harvesting in micro-/nano-electro-mechanical systems (MEMS/NEMS). Therein, the characteristics of the microscale and multi-physical aspects effect significant influence on performance, such as attaining a fast response and high power density. It is difficult to use the classical mechanical and heat conduction models to effectively explain and analyze microscale physical field coupling behaviors. The purpose of this study is to develop the piezoelectric thermoelastic theoretical model, firstly considering the non-uniform physical field. The generalized equations governing thermo-electro-elastic vibration energy harvesting in a microbeam model were obtained based on Hamilton's principle and the generalized thermoelastic theory was developed by considering thermopolarization and thermal hysteresis behavior. After that, the explicit expressions for voltage and output power were derived using the assumed-modes method; meanwhile, effects such as the piezo-flexoelectric aspect, size dependence, etc. are discussed in detail. It was found that thermal and microscale effects significantly promote the voltage and output power. The research is also helpful for the design and optimization of self-powered and high-performance micro/nano devices and systems. [ABSTRACT FROM AUTHOR]

Nanocomposite materials, such as graphene nanoplatelets (GPLs), have been fabricated into high-efficient resonators due to the excellent thermo-mechanical properties. In addition, thermoelastic damping (TED), as a dominant intrinsic dissipation mechanisms, is a major challenge in optimizing high-performance micro-/nano-resonators. Nevertheless, the classical TED models fail on the micro-/nano-scale due to not considering the influences of the size-dependent effect and the thermal lagging effect. To fill these gaps, the present work aims to investigate TED analysis of functionally graded (FG) polymer microplate resonators reinforced with GPLs based on the modified couple stress theory (MCST) and the three-phase-lag (TPL) heat conduction model. Four patterns of GPL distribution including the UD, FG-O, FG-X, and FG-A pattern distributions are taken into account, and the effective mechanical properties of the plate-type nanocomposite are evaluated based on the Halpin-Tsai model. The energy equation and the transverse motion equation in the Kirchhoff microplate model are formulated, and then, the analytical solution of TED is solved by complex frequency method. The influences of the various parameters involving the material length-scale parameter, the phase-lag parameters, and the total weight fraction of GPLs on the TED are discussed in detail. The obtained results show that the effects of the modified parameter on the TED are pronounced. This paper provides a theoretical approach to estimate TED in the design of high-performance micro-resonators. [ABSTRACT FROM AUTHOR]

With the size reduction of structures into micro/nanoscale, the size-dependent effect arises in mechanical properties. For micro/nanostructures working in transient thermal environment, the thermal relaxation needs to be considered in heat conduction. Functionally graded carbon nanotubes/graphene platelets reinforced composite (FG-CNTRC/GPLRC) materials as new generation of advanced materials have attracted much attention due to their excellent mechanical or thermoelastic performance. Though the mechanical or non-coupled thermoelastic behaviors of beam, plate and shell made of FG-CNTRC/GPLRC materials have been extensively studied, there lacks of investigations on the coupled thermoelastic behaviors of micro/nanostructures of FG-CNTRC/GPLRC in the context of generalized thermoelasticity where both the elastic nonlocality and thermal relaxation need to be considered. To fill this gap, in this work, the Lord–Shulman (L-S) type generalized thermoelasticity incorporating the fractional-order nonlocal theory is applied to investigating the thermoelastic bending wave propagation characteristics of a nanocomposite microbeam reinforced by GPLs and CNTs simultaneously for the first time. The Halpin–Tsai micromechanical model is used to assess the effective elastic modulus and the other properties are evaluated by the rule of mixture. Then, the governing equations are formulated based on the Euler–Bernoulli beam model. By assuming the wave-type solutions, the governing equations are solved and the dispersion relation between frequency and wave number and the relation between phase velocity and wave number are determined, respectively. In calculation, the effects of the thermal relaxation time, the elastic nonlocal parameter, the fractional order parameter and the mass fractions of GPLs and CNTs on the dimensionless frequency and phase velocity are analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

For small-sized structures or devices, size-dependent effect and thermal-induced deformation become the main concerns in guiding their practical applications. To reveal such concerns of porous structures, the dynamic response of a finite porous microrod, subjected to a moving heat source and fixed at both ends, is investigated based on the non-local elasticity theory and the theory for porous materials with thermal relaxation. The corresponding governing equations are formulated and solved using Laplace transform and its numerical inversion. The distributions of the non-dimensional temperature displacement stress and volume fraction are obtained and illustrated graphically. In the simulation, the effects of the non-local parameter, the velocity of the heat source, and the thermal lag factor on the considered quantities are examined and illustrated graphically. Comparisons between the microrod with voids and without voids are shown. [ABSTRACT FROM AUTHOR]

AbstractHollow cylinder structures play a crucial role in scientific experiment and industrial production, and are widely used in various fields, including pipeline transportation of gases and liquids, high-speed engines, porous combustors, and other engineering equipments. As a result, they have garnered considerable academic interest over the years. However, as science and technology progress, studying hollow cylinders under a single physical field is no longer sufficient for real-world applications. Additionally, the classical viscoelastic model has become inadequate in accurately describing complex materials with properties that fall between elasticity and viscosity. Therefore, this article investigates the electro-magneto-thermoviscoelastic coupling behavior of an infinitely long rotating multilayer homogeneous hollow cylindrical conductor. In this study, based on the fractional-order three-phase lag thermoelasticity theory, the fractional-order viscoelastic system and the two-temperature theory are introduced to further increase the accuracy of the model. To solve the corresponding equations, the Laplace transform technique is employed, resulting in solutions with dimensionless physical quantities. Graphs and tables are used to make relevant comparisons and assess the effects of time, material layering properties, different thermoelastic theoretical models, fractional-order parameters and angular velocity on the considered physical quantities. Finally, the numerical results are discussed to reveal the dynamic response of a homogeneous multilayered hollow cylinder under the complex coupling of multiple physical fields. [ABSTRACT FROM AUTHOR]

In response to a series of engineering disasters encountered during the excavation and support construction of loess tunnels, considering the issues of water enrichment in surrounding rock induced by excavation disturbance and system bolt failure, drawing on the concepts of lime pile composite foundation and composite bearing arch, and based on the principle of the New Austrian Tunneling Method (NATM) that fully mobilizes and leverages the self-supporting capacity of surrounding rock, this study comprehensively considers the wetting and stress adjustment processes of the surrounding rock after excavation disturbance in loess tunnels. By adopting the technical principle of "water absorption and densification of shallow surrounding rock, suspension and anchoring of deep surrounding rock, and composite arch bearing", a new type of water-absorbing, densifying, and anchoring bolt was developed that can reduce the water content of surrounding rock while enhancing its resistance. To further investigate the water absorption, densification effect, and pull-out bearing characteristics of this new bolt, laboratory model tests were conducted, examining the temperature, pore water pressure, densification stress of the soil around the bolt, as well as the physical properties of the soil in the consolidation zone. The test results indicate that a cylindrical heat source forms around the water-absorbing, densifying, and anchoring bolt, significantly inducing the thermal consolidation of the surrounding soil. The variations in temperature, pore water pressure, and densification stress of the soil around the bolt truly reflect the qualitative patterns of hydro-thermal–mechanical changes during the water absorption, curing, and exothermic reaction processes. The water absorption and densification segment of the bolt effectively enhances the density of the soil in the water absorption, densification, and consolidation zone, improving soil strength parameters. Compared to traditional mortar-bonded bolts, the water-absorbing, densifying, and anchoring bolt exhibits a greater pull-out bearing capacity. The research findings provide important guidance for the theoretical design and engineering application of this new type of bolt. [ABSTRACT FROM AUTHOR]

The accurate representation of real floor behavior is crucial for assessing human-induced vibration serviceability. Many researchers focus on developing computational models and field testing to reflect actual serviceability conditions. Although traditional boundary conditions are commonly used, limited attention has been given to optimizing these conditions. To begin with, this paper introduced semirigid boundary conditions into a finite-element model of the floor and optimized physical parameters and boundary constraint stiffness using the simulated annealing-particle swarm optimization (SA-PSO) method, resulting in a more realistic computational model. Subsequently, a random crowd load model was established by combining the social force model (SFM) and the pedestrian load model, and a random crowd-floor mutual coupling calculation model was established based on the improved pedestrian biomechanical model. In addition, the mode shape functions of the floor with semirigid boundary conditions were obtained by extracting the optimized mode shape vector of the floor and using cubic spline interpolation. The dynamic response of the floor was computed using the modal analysis method, and the accuracy of the suggested method and model was verified by experiment. Furthermore, the effect on the vibration serviceability of the floor was analyzed under crowd walks randomly on the floor with different boundary conditions both before and after optimization. This study revealed: (1) achieving a computational model consistent with real floors requires optimization of relevant parameters and boundary conditions, reducing the error in floor frequency from 39.48% to 5.44% compared to measured results. (2) The human-induced vibration serviceability for existing floors may be misjudged by using traditional boundary conditions. The mean value of peak acceleration of floor with semirigid boundary conditions increased by 35.92%, with a 42% increase in the probability of serviceability problems compared to the SSCC boundary. (3) High-frequency floors also experience human-induced vibration serviceability issues. For a floor with a fundamental frequency of 10.3540 Hz, simulation and experimental results during five-person random walks indicate that peak acceleration at the middle position of the floor exceeds serviceability limits. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets (GPLs) are considered to be a desirable reinforcing nanofillers for nanocomposite materials owing to their superior thermo‐mechanical properties. Meanwhile, thermoelastic damping (TED), as a dominant intrinsic dissipation mechanisms, is a major challenge in optimizing high‐performance micro/nano‐resonators. Nevertheless, the classical TED models fail at the micro/nano‐scale due to without considering the influences of the size‐dependent effect and the thermal lagging effect. The present work focuses on investigating TED analysis of functionally graded (FG) microplate resonators reinforced with GPLs based on the modified coupled stress theory (MCST) and the Moore–Gibson–Thompson (MGT) heat conduction model. Four patterns of GPLs distribution including the UD, FG‐O, FG‐X and FG‐A pattern distributions are taken into account and the effective mechanical properties of the plate‐type nanocomposite are evaluated based on the Halpin–Tsai model. The energy equation and the transverse motion equation in the Kirchhoff microplate model are formulated, and then, the closed‐from analytical solution of TED is solved by complex frequency method. The influences of the various parameters involving the material length‐scale parameter, the thermal phase lag of the heat flux and the total weight fraction of GPLs on the TED are discussed in detail. The obtained results show that the effects of the modified parameter on the TED are pronounced. This results provide a more reasonable theoretical approach to estimate TED in the design of FG microplate resonators reinforced with GPLs with high performance. [ABSTRACT FROM AUTHOR]