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1

Thermoelastic vibration characteristics of asymmetric annular porous reinforced with nano-fillers microplates embedded in an elastic medium: CNTs Vs. GNPs

Arshid Ehsan, Amir Saeed, Loghman Abbas

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e100, 2023

EN

Due to the vast usage of metal foam structures in branches of science, reinforcing them with nano-fillers makes them more convenient. Hence, in the current study, vibration characteristics of functionally graded porous nanocomposite (FGPN) annular microplates are taken into consideration. Two kinds of nano-fillers, namely Carbon nanotubes (CNTs) and Graphene nanoplatelets (GNPs), are selected as the reinforcements to analyze and compare their effect on the microstructure’s vibrational response. The mentioned nano-fillers are dispersed according to four patterns which affect various mechanical properties of the structure. Similarly, based on given functions which are called porosity distributions, pores are placed in thickness course of the microstructure. Then, its properties are determined via employing Halpin-Tsai and extended rule of mixture micromechanics models. Using the first-order shear deformation theory (FSDT), modified couple stress theory (MCST), and Hamilton’s principle for dynamic systems, governing motion equations and related boundary conditions are derived in asymmetric state, and then, they are solved, and natural frequencies and corresponding mode shapes are extracted with the help of generalized differential quadrature method (GDQM). By validating the results in simpler conditions, effects of the most important parameters are examined. It is found that GNPs are more effective in reinforcing the structure than CNTs. Also, about 15~18 percent reduction in frequencies is seen by increasing the porosity up to seventy percent.

2

Couple stress-based thermoelastic damping in microrings with rectangular cross section according to Moore–Gibson–Thompson heat equation

Al‑Bahrani Mohammed, AbdulAmeer Sabah Auda, Yasin Yaser, Alanssari Ali Ihsan, Hameed Asaad Shakir, Sulaiman Jameel Mohammed Ameen, Hussein Mohamed J., Alam Mohammad Mahtab

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e151, 2023

EN

It has been confirmed that structures with micro dimensions display size-dependent thermomechanical behaviors. Moreover, according to the findings of empirical and theoretical researches, thermoelastic damping (TED) has been recognized as one of inescapable causes of energy dissipation in microstructures. The current article is an effort to provide a novel size-dependent framework for approximating the amount of TED in microring resonators with rectangular cross section. To include size effect into structural and thermal constitutive relations, the modified couple stress theory (MCST) and the Moore–Gibson–Thompson (MGT) heat equation are utilized, respectively. By solving the coupled heat equation in the purview of MGT model, the fluctuation temperature throughout the ring is determined. By employing the obtained temperature distribution and constitutive relations of MCST, the peak values of strain and wasted thermal energies during one cycle of vibration are computed. Based on the description of TED in the energy dissipation (ED) method, a mathematical expression containing the scale parameters of MCST and MGT model is derived for estimating TED value. To ensure the correctness and veracity of the established solution, a comparative study is carried out on the basis of the data released by other researchers for more plain models. A section is also designated for an all-out study to ascertain the association between TED spectrum and some influential factors like scale parameters of MCST and MGT model, vibration mode number, one-dimensional (1D) and two-dimensional (2D) heat conduction, geometry and material. The extracted data enlighten that the impact of applying MCST and MGT model on TED has a close relationship with the vibration mode number of the ring.

3

Transient dynamic analysis of functionally graded micro-beams considering small-scale effects

Eshraghi I., Dag S.

Archives of Mechanics

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2021

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Vol. 73, nr 4

303--337

EN

A domain-boundary element method, based on modified couple stress theory, is developed for transient dynamic analysis of functionally graded micro-beams. Incorporating static fundamental solutions as weight functions in weighted residual expressions, governing partial differential equations of motion are converted to a set of coupled integral equations. A system of ordinary differential equations in time is obtained by domain discretization and solved using the Houbolt time marching scheme. Developed procedures are verified through comparisons to the results available in the literature for micro- and macro-scale beams. Numerical results illustrate elastodynamic responses of graded micro-beams subjected to various loading types. It is shown that metal-rich micro-beams and those with a smaller length scale parameter ratio undergo higher displacements and are subjected to larger normal stresses.

4

Free vibration and buckling analyses of FG porous sandwich curved microbeams in thermal environment under magnetic field based on modified couple stress theory

Arshid Ehsan, Arshid Hossein, Amir Saeed, Mousavi S. Behnam

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

89--111

EN

Porous sandwich structures include different numbers of layers and are capable of demonstrating higher values of strength to weight ratio in comparison with traditional sandwich structures. Free vibration and mechanical buckling responses of a three-layered curved microbeam was investigated under the Lorentz magnetic load in the current study. A viscoelastic substrate was considered and the effect of the thermal environment on its mechanical properties was assessed. The core was composed of the functionally graded porous materials whose properties changed across the thickness based on some given functions. The face sheets were FG-carbon nanotube-reinforced composites and the influence of the placement of CNTs was evaluated on the behavior of the faces. Using the extended rule of mixture, their effective properties were determined. Modified couple stress theory was used to predict the results in the micro-dimension. While the governing equations were derived based on the higher order shear deformation theory and energy method, and mathematically solved via Navier’s method. The results were validated with the previously published works, considering the effects of various parameters. As comprehensively explained in the results section, natural frequencies and critical buckling loads were reduced by enhancing the central opening angle. Moreover, an increase in the porosity coefficient declined the mentioned values, but increasing the CNTs content showed the opposite effect. The outcomes of this study may help in the design and manufacturing of various equipment using such smart structures, making high stiffness to weight ratios more accessible.

5

Resonance of nanoscale beam due to various sources in modified couple stress thermoelastic diffusion with phase lags

Kumar Rajneesh, Devi Shaloo, Sharma Veena

Mechanics and Mechanical Engineering

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2019

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Vol. 23, nr 1

36--49

EN

This paper deals with the study of thermoelastic thin beam in a modified couple stress with three-phaselag thermoelastic diffusion model subjected to thermal and chemical potential sources. The governing equations are derived by using the Euler-Bernoulli beam assumption and eigenvalue approach. The Laplace transform technique is employed to obtain the expressions for displacements, lateral deflection, temperature change, axial stress and chemical potential. A particular type of instantaneous and distributed sources is taken to show the utility of the approach. The general algorithm of the inverse Laplace transform is developed to compute the results numerically. The numerical results are depicted graphically to show the effects of phase lags, with and without energy dissipation on the resulting quantities. Some special cases are given.

6

Free vibration of a hyper-elastic microbeam using a new “augmented Biderman model”

Karami Mohammadi Ardeshir, Danaee Barforooshi Saeed

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 3

739--750

EN

A new augmented Biderman model inspired by the modified couple stress theory has been introduced to investigate the size effect in addition to nonlinear material effects. Then, this model is used to investigate free vibration of a hyper-elastic microbeam. Classical Biderman strain energy does not include the effect of small size in hyper-elastic materials. In order to consider the effect of small size, terms inspired by the modified couple stress theory are added to the classical Biderman strain energy function. In order to provide the possibility of calculating these terms, a relation between the material constants in the hyper-elastic Biderman model and the linear elastic constants is obtained. The equations of motion of the microbeam is obtained based on the extended Hamilton principle, and then is solved using Galerkin discretization and perturbation methods. The effect of thickness to length scale ratio on the normalized frequency is studied for different modes. It is shown that when thickness gets larger in comparison with the length scale parameter, the normalized frequency tends to classical Biderman results. The results obtained are validated by results of the Runge-Kutta numerical method and indicate an excellent agreement. Mode shapes of the microbeam based on the classical and the augmented models are depicted, where the augmented model anticipates stiffer behavior for hyperelastic microbeams.

7

Deformation of modified couple stress thermoelastic diffusion in a thick circular plate due to heat sources

Kumar R., Devi S.

Computational Methods in Science and Technology

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2019

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Vol. 25, No. 4

167--176

EN

The aim of this study is to present a mathematical model for predicting the results for displacements, stress components, temperature change and chemical potential with considering independently a particular type of heat source. The general solution for the two-dimensional problem of a thick circular plate with heat sources in modified couple stress thermoelastic diffusion has been obtained in the context of one and two relaxation times. Laplace and Hankel transforms technique is applied to obtain the solutions of the governing equations. Resulting quantities are obtained in the transformed domain. The numerical inversion technique has been used to obtain the solutions in the physical domain. Effects of time on the resulting quantities are shown graphically.

8

Vibration analysis of nanotubes based on two-node size dependent axisymmetric shell element

Soleimani I., Beni Y. T.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1345--1358

EN

In this paper, size dependent axisymmetric shell element formulation is developed by using the modified couple stress theory in place of classical continuum theory. Since the study of nanoshells is conducted in nanodimensions, the mechanical properties of nanoshells are size dependent; therefore, taking into consideration the size effect, nonclassical continuum theories are used. In the present work the mass–stiffness matrix for axisymmetric shell element is developed, and by means of size-dependent finite element, the formulation is extended to more precisely account for nanotube vibration. It is shown that the classical axisymmetric shell element can also be defined by setting length scale parameter to zero in the equations. The results show that the rigidity of the nanoshell in the modified couple stress theory is greater than that in classical continuum theory, which leads to the increase in natural frequencies. The findings also indicate that the developed size dependent axisymmetric shell element is able to cover both cylindrical and conical shell elements and is reliable for simulating micro/nanoshells. Using size dependent axisymmetric shell element increases convergence speed and accuracy in addition to reducing the number of the required elements.

9

A multi-spring model for buckling analysis of cracked Timoshenko nanobeams based on modified couple stress theory

Akbarzadeh Khorshidi M., Shariati M.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 4

1127--1139

EN

This paper develops a cracked nanobeam model and presents buckling analysis of this developed model based on a modified couple stress theory. The Timoshenko beam theory and simply supported boundary conditions are considered. This nonclassical model contains a material length scale parameter and can interpret the size effect. The cracked nanobeam is modeled as two segments connected by two equivalent springs (longitudinal and rotational). This model promotes discontinuity in rotation of the beam and additionally considers discontinuity in longitudinal displacement due to presence of the crack. Therefore, this multi-spring model can consider coupled effects between the axial force and bending moment at the cracked section. The generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations, boundary and continuity conditions. The influences of crack location, crack severity, material length scale parameter and flexibility constants of the presented spring model on the critical buckling load are studied.

10

Nonlinear Free Vibration Analysis of Micro-beams Resting on Viscoelastic Foundation Based on the Modified Couple Stress Theory

Jam J. E., Noorabadi M., Namdaran N.

Archive of Mechanical Engineering

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2017

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Vol. LXIV, nr 2

239--256

EN

In this paper, nonlinear free vibration analysis of micro-beams resting on the viscoelastic foundation is investigated by the use of the modified couple stress theory, which is able to capture the size effects for structures in micron and sub-micron scales. To this aim, the governing equation of motion and the boundary conditions are derived using the Euler–Bernoulli beam and the Hamilton’s principle. The Galerkin method is employed to solve the governing nonlinear differential equation and obtain the frequency-amplitude algebraic equation. Finally, the effects of different parameters, such as the mode number, aspect ratio of length to height, the normalized length scale parameter and foundation parameters on the natural frequency-amplitude curves of doubly simply supported beams are studied.

11

Response of Thermoelastic Beam due to Thermal Source in Modified Couple Stress Theory

Rajneesh K.

Computational Methods in Science and Technology

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2016

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Vol. 22, No. 2

95--101

EN

The present investigation deals with the problem of thermoelastic beam in the modified couple stress theory due to thermal source. The governing equations of motion for the modified couple stress theory and heat conduction equation for coupled thermoelasticity are investigated to model the vibrations in a homogeneous isotropic thin beam in a closed form by applying the Euler Bernoulli beam theory. The Laplace transform technique is used to solve the problem. The lateral deflection, thermal moment, axial stress average due to normal heat flux in the beam are derived and computed numerically. The resulting quantities are depicted graphically for a specific model. A particular case is also introduced.

12

Nonlinear motion characteristics of microarches under axial loads based on modified couple stress theory

Farokhi H., Ghayesh M. H.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 2

401--411

EN

The aim of the present study is to investigate the geometrically nonlinear size-dependent bending as well as resonant behaviour over the bent state of a microarch under an axial load. In particular, an axial load is applied on the system causing the initial curvature to increase by giving rise to a new bent configuration. A distributed harmonic transverse force is then exerted on the microarch and the nonlinear resonant response of the system over the new deflected configuration is investigated. The nonlinear partial differential equation of motion is obtained via Hamilton's principle based on the modified couple stress theory. The equation is discretized into a set of nonlinear ordinary differential equations through use of the Galerkin scheme. The pseudo-arclength continuation technique is then applied to the resultant set of ordinary differential equations. First, for the unforced system in the transverse direction, the axial load is increased and the new deflected configuration of the system is plotted versus the axial compression load; the nonlinear resonant response over the deflected configuration is then investigated through constructing frequency–response and force–response curves.