Alaa Ahmed - Academia.edu (original) (raw)

Papers by Alaa Ahmed

Research paper thumbnail of On Bending of Piezoelectrically Layered Perforated Nanobeams Embedded in an Elastic Foundation with Flexoelectricity

Mathematics

Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural co... more Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural components with flexoelectricity has been considered by many researchers because of the developments of nanotechnology and the applicability of piezoelectric composite nanobeam structures in Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). Therefore, the work investigates the size-dependent electromechanical bending of piezoelectrically layered perforated nanobeams resting on elastic foundations including the flexoelectric effect. Within the framework of the modified nonlocal strain gradient elasticity theory, both the microstructure and nonlocality effects are captured. The governing equilibrium equations including piezoelectric and flexoelectric effects are derived using Hamilton’s principle. Closed forms for the non-classical electromechanical bending profiles are derived. The accuracy of the proposed methodology is verified by comparing the obtained results with the available corresp...

Research paper thumbnail of Improvement of spacecraft structure Dynamic Characteristics by Using Honeycomb Sandwich panels

Egyptian Journal for Engineering Sciences and Technology, 2020

Honeycomb cored structures are considered one of the most efficient composite structures which ar... more Honeycomb cored structures are considered one of the most efficient composite structures which are commonly used in different industrial applications. These structures are characterized by high strength to weight ratio and good impact resistance thus it is suitable for aerospace structures. Structural properties of honeycomb structure depend on its lower, upper skin sheet thickness, the core material thickness, cell dimension, cell angle and foil thickness. Using of honeycomb structure panels in satellite main structure provide the opportunity to reduce satellite mass in significant manner. This study concerns with the static and dynamic performance of honeycomb sandwich panel structures and its applications in spacecraft construction. This work studies the static and dynamics characteristics of a spacecraft structure including an intermediate plate made of two different materials; the first one with an Aluminum intermediate sandwich plate while the second with honeycomb sandwich plate. The obtained results show that the satellite structure supported with honeycomb intermediate plate produces higher value of the fundamental resonant frequencies compared to the corresponding ones in satellite structure with Aluminum intermediate plate which is better for the launch vehicle requirements. Moreover, the spacecraft structure mass was reduced by around 15%.

Research paper thumbnail of A Dynamic Analysis of Randomly Oriented Functionally Graded Carbon Nanotubes/Fiber-Reinforced Composite Laminated Shells with Different Geometries

Mathematics, 2022

The present study demonstrates the free vibration behavior of composite laminated shells reinforc... more The present study demonstrates the free vibration behavior of composite laminated shells reinforced by both randomly oriented single-walled carbon nanotubes (SWCNTs) and functionally graded fibers. The shell structures with different principal radii of curvature are considered, such as cylindrical, spherical, elliptical–paraboloid shell, hyperbolic–paraboloid shell, and plate. The volume fraction of the fibers has a linear variation along the shell thickness from layer to layer, while the volume fraction of CNTs is constant in all shell layers and uniformly distributed. The fiber-reinforced elements are distributed with three functions which are V-distribution, O-distribution, and X-distribution in addition to the uniform distribution. A numerical analysis was carried out systematically to validate the proposed solution. A new analytical solution is presented based on the Galerkin approach for shells and is exploited to illustrate the influence of some factors on the free vibration ...

Research paper thumbnail of Dynamic Analysis of a Piezoelectrically Layered Perforated Nonlocal Strain Gradient Nanobeam with Flexoelectricity

Mathematics

This study presents a mathematical size-dependent model capable of investigating the dynamic beha... more This study presents a mathematical size-dependent model capable of investigating the dynamic behavior of a sandwich perforated nanobeam incorporating the flexoelectricity effect. The nonlocal strain gradient elasticity theory is developed for both continuum mechanics and flexoelectricity. Closed forms of the equivalent perforated geometrical variables are developed. The Hamiltonian principle is exploited to derive the governing equation of motion of the sandwich beam including the flexoelectric effect. Closed forms for the eigen values are derived for different boundary conditions. The accuracy of the developed model is verified by comparing the obtained results with the available published results. Parametric studies are conducted to explore the effects of the perforation parameters, geometric dimensions, nonclassical parameters, flexoelectric parameters, as well as the piezoelectric parameters on the vibration behavior of a piezoelectric perforated sandwich nanobeam. The obtained ...

Research paper thumbnail of Dynamic analysis of nanoscale Timoshenko CNTs based on doublet mechanics under moving load

The European Physical Journal Plus, 2021

The novelty of this article is to investigate the dynamic behavior and response of armchair and z... more The novelty of this article is to investigate the dynamic behavior and response of armchair and zigzag carbon nanotubes (CNTs) under the dynamic moving load using a bottom to up modeling nano-mechanics theory. CNTs are modeled as a Timoshenko beam structure with shear deformation effect, and the size influence of CNTs imposed using the doublet mechanics theory. Hamiltonian principle is used to derive the modified equation of motion and nonclassical boundary conditions of CNTs under moving loads. Analytical Navier method solution for simply supported CNTs beam and Newmark time integration method are developed to predict the response of the structure in time-domain. The proposed model is verified and proved with previously published works for free vibration. Parametric analysis is performed to illustrate the influence of doublet length scale, structures of CNTs, load velocities, and mass of the load on the dynamic responses of CNTs. The proposed model is useful in designing and analyzing of MEMS/NEMS, nano-sensor, and nano-actuator manufactured from CNTs.

Research paper thumbnail of Dynamics of perforated higher order nanobeams subject to moving load using the nonlocal strain gradient theory

Smart Structures and Systems, 2021

The goal of this manuscript is to develop a nonclassical size dependent model to study and analyz... more The goal of this manuscript is to develop a nonclassical size dependent model to study and analyze the dynamic behaviour of the perforated Reddy nanobeam under moving load including the length scale and microstructure effects, that not considered before. The kinematic assumption of the third order shear deformation beam theory in conjunction with modified continuum constitutive equation of nonlocal strain gradient (NLSG) elasticity are proposed to derive the equation of motion of nanobeam included size scale (nonlocal) and microstructure (strain gradient) effects. Mathematical expressions for the equivalent geometrical parameters due to the perforation process of regular squared pattern are developed. Based on the virtual work principle, the governing equations of motion of perforated Reddy nanobeams are derived. Based on Navier's approach, an analytical solution procedure is developed to obtain free and forced vibration response under moving load. The developed methodology is v...

Research paper thumbnail of Effects of viscoelastic bonding layer on performance of piezoelectric actuator attached to elastic structure

Materials Research Express, 2022

In the context of the finite elements analysis, the mechanical performance of viscoelastically bo... more In the context of the finite elements analysis, the mechanical performance of viscoelastically bonded smart structures is investigated and analyzed. Three different models are considered and compared. In the 1st model, the actuator is glued to the host structure. On the other hand, in the two other models the actuator is glued to the bonding layer which is glued to the host structures. To explore the effect of the bonding layer characteristics on the mechanical behavior of the host structure, both elastic and viscoelastic layers are considered. The Prony’s series are utilized to simulate the viscoelastic constitutive response. The mathematical formulation of the coupled problem is presented and the dynamic finite elements equations of motion of the coupled electromechanical systems are introduced. The proposed methodology is verified by comparing the obtained results with the available results in the literature and good consentience is observed. Both static and dynamic vibration beh...

Research paper thumbnail of Modeling and analysis of the transient response of viscoelastic solids

Waves in Random and Complex Media, 2020

In this paper, an incremental finite element model (IFEM) for the transient analysis of viscoelas... more In this paper, an incremental finite element model (IFEM) for the transient analysis of viscoelastic solids is developed. The viscoelastic constitutive response is modeled based on the hereditary integral. Two new incremental constitutive forms suitable for finite element implementation are derived; creep-based (CB) and relaxation-based (RB) and, as a consequent, the difficulties associated with the interconversion from the relaxation modulus to the creep compliance and vice versa are avoided. Creep compliance and relaxation modulus are, respectively, modeled using generalized Kelvin-Voigt model and generalized Wiechert's model. To check the validity, the computational procedure, semi-analytical solution is derived for simple viscoelastic cases using Laplace and inverse Laplace transform techniques. The obtained results from the computational procedure are compared with that obtained from the derived semi-analytical solution. To show the validity and applicability of the developed model, two different applications under different excitation patterns are presented. In each application, the time response for displacements and stresses, especially for the dynamic stress concentration factor for both elastic and viscoelastic analyses are investigated. Moreover, the dissipative recoverable nature of the viscoelastic solids under different loading-unloading excitation patterns is illustrated.

Research paper thumbnail of On bending analysis of perforated microbeams including the microstructure effects

Structural Engineering and Mechanics, 2020

This article presents a nonclassical size dependent model based on the modified couple stress the... more This article presents a nonclassical size dependent model based on the modified couple stress theory to study and analyze the bending behavior of perforated microbeams under different loading patterns. Modified equivalent material and geometrical parameters for perforated beam are presented. The modified couple stress theory with one material length scale parameter is adopted to incorporate the microstructure effect into the governing equations of perforated beam structure. The governing equilibrium equations of the perforated Timoshenko as well as the perforated Euler Bernoulli are developed based on the potential energy minimization principle. The Poisson’s effect is included in the governing equilibrium equations. Regular square perforation configuration is considered. Based on Fourier series expansion, closed forms for the bending deflection and the rotational displacements are obtained for simply supported perforated microbeams. The proposed methodology is validated and compare...

Research paper thumbnail of Bending behavior of squared cutout nanobeams incorporating surface stress effects

Steel and Composite Structures, 2020

In nanosized structures as the surface area to the bulk volume ratio increases the classical cont... more In nanosized structures as the surface area to the bulk volume ratio increases the classical continuum mechanics approaches fails to investigate the mechanical behavior of such structures. In perforated nanobeam structures, more decrease in the bulk volume is obtained due to perforation process thus nonclassical continuum approaches should be employed for reliable investigation of the mechanical behavior these structures. This article introduces an analytical methodology to investigate the size dependent, surface energy, and perforation impacts on the nonclassical bending behavior of regularly squared cutout nanobeam structures for the first time. To do this, geometrical model for both bulk and surface characteristics is developed for regularly squared perforated nanobeams. Based on the proposed geometrical model, the nonclassical Gurtin-Murdoch surface elasticity model is adopted and modified to incorporate the surface energy effects in perforated nanobeams. To investigate the effe...

Research paper thumbnail of Stability of perforated nanobeams incorporating surface energy effects

Steel and Composite Structures, 2020

Research paper thumbnail of Vibration response of symmetric and sigmoid functionally graded beam rested on elastic foundation under moving point mass

Mechanics Based Design of Structures and Machines, 2021

Research paper thumbnail of Dynamics analysis of timoshenko perforated microbeams under moving loads

Engineering with Computers, 2020

This paper aims to present a modified continuum mathematical model capable on investigation of dy... more This paper aims to present a modified continuum mathematical model capable on investigation of dynamic behavior and response of perforated microbeam under the effect of moving mass/load for the first time. A size-dependent finite element model with non-classical shape function is exploited to solve the mathematical model and obtain the dynamic response of perforated Timoshenko microbeams under moving loads. To that end, first, equivalent material and geometrical parameters for perforated beam are developed, based on the regular squared perforation configuration. Second, both the stiffness and mass property matrices including the microstructure effect based on modified couple stress theory and Timoshenko first-order shear beam theory are derived for two-node finite element using new shape function. After that, the interaction between the load and beam is modeed and unified with the equation of motion of the beam incorporating mass inertia effects of moving load. The developed procedure is validated and compared. Effects of perforation parameters, moving load velocities, inertia of mass, and the microstructure size parameter on the dynamic response of perforated microbeam structures have been investigated in a wide context. The achieved results are helpful for the design and production of MEMS structures such as frequency filters, resonators, relay switches, accelerometers and mass flow sensors, with perforation.

Research paper thumbnail of Static bending of perforated nanobeams including surface energy and microstructure effects

Engineering with Computers, 2020

This article aims to present comprehensive model and analytical solution to investigate the stati... more This article aims to present comprehensive model and analytical solution to investigate the static bending behavior of regularly squared cutout perforated thin/thick nanobeams incorporating the coupled effect of the microstructure and surface energy for the first time. The perforation influence is considered to be deriving equivalent geometrical and material characteristics. The modified couple stress theory is adopted to incorporate the microstructure effect while the modified Gurtin-Murdoch surface elasticity model is employed to incorporate the surface stress effect in perforated nanobeams. A variational formulation based on minimization of the total potential energy principle is employed to derive the equilibrium equations of perforated nanobeams based on both Euler-Bernoulli and Timoshenko beams theories are developed to investigate the associated effect of the shear deformation due to perforation process. Additionally, Poisson's effect is also incorporated. Analytical closed-form for the non-classical bending profiles as well as the rotational displacement are developed for both beam theories considering the simultaneous effect of both couple stress and surface stress for both uniformly distributed and concentrated loading patterns. The verification of the developed model is verified and compared with previous works, and an excellent agreement is obtained. The applicability of the developed model is demonstrated and applied to study and analyze the nonclassical bending behavior of regularly squared perforated simply supported beams under different loading conditions. Additionally, effects of the perforation configuration parameters, beam size as well as beam aspect ratio on the bending behavior of perforated beams in the presence of microstructure and surface stress effects are also investigated and analyzed. The obtained results reveal that both couple stress and surface stress significantly affect the bending behavior of regularly squared cutout perforated beam structures. Results obtained are supportive for the design, analysis and manufacturing of perforated NEMS applications.

Research paper thumbnail of Influence of the perforation configuration on dynamic behaviors of multilayered beam structure

Structures, 2020

The novelty of this paper is to investigates the free vibration, frequency response and modal par... more The novelty of this paper is to investigates the free vibration, frequency response and modal participation factors of the perforated multilayer microbeam structures using finite element analysis with different hole's geometry, filling ratio and array of hole. The three squared, rectangular, and circular configurations of perforation are considered through analysis. Elasto-dynamic finite element formulation is implemented. The natural frequencies for the three different perforation configurations at different number of holes are investigated. For better understanding of the dynamic behavior of multilayered perforated beam structure, both modal and harmonic responses are presented and discussed. To specify the most suitable vibrational mode for a certain degree of freedom for base excitation, both participation factor and the associated modal effective mass are presented and analyzed. The obtained results show the remarkable effect of perforation configuration and the number of holes throughout the cross-sectional area on the dynamic behavior of multilayered perforated beam structures. Different boundary conditions are considered through analysis. The obtained results are supportive for the design of perforated beam structures in both macro and micro-scales.

Research paper thumbnail of Dynamics of perforated nanobeams subject to moving mass using the nonlocal strain gradient theory

Applied Mathematical Modelling, 2021

Abstract In the present manuscript, based on the nonlocal strain gradient theory, a nonclassical ... more Abstract In the present manuscript, based on the nonlocal strain gradient theory, a nonclassical dynamic finite element model is developed to study and analyze the dynamic behavior of perforated nanobeam structures under moving mass/load. In the context of nonclassical continuum mechanics and Timoshenko beam theory, dynamic equations of motion of perforated nanobeams are derived including both size scale (nonlocal) and microstructure (strain gradient) effects. The modification of the geometrical parameters due to the perforation process is included in the equations of motion for squared holes arranged in the arrayed form. The effect of the moving mass (the inertia, Coriolis and centripetal forces, and the gravity force) or moving load are included in the proposed model. To remove shear locking problem in slender nanobeams, finite element model on nonclassical shape function basis is developed. Elements stiffness and mass matrices and force vector including the nonlocal and strain gradient effects are derived. The proposed model is verified and checked with previous works. Impacts of perforation, mass/load velocities, inertia of mass, microstructure parameter and nonlocal size scale effects on the dynamic and vibration responses of perforated nanobeam structures have been investigated in a wide context. The following model is beneficial for the design of MEMS/NEMS structures such as frequency filters, resonators, relay switches, accelerometers, and mass flow sensors, with perforation.

Research paper thumbnail of Vibration response of Timoshenko perforated microbeams under accelerating load and thermal environment

Applied Mathematics and Computation, 2021

Research paper thumbnail of Nonlinear dynamics of viscoelastic flexible structural systems by finite element method

Engineering with Computers, 2020

This article presents a nonlinear displacement based finite elements model to study and analyze t... more This article presents a nonlinear displacement based finite elements model to study and analyze the nonlinear dynamic response of flexible double wishbone structural vehicle suspension system considering damping effect which was not previously discussed elsewhere. Due to large deflection and moderate rotation encountered during passing over road bumps, the kinematic nonlinearity is included through von Kármán strain component. Elastic undamped as well as viscous and viscoelastic damping mechanism are considered and compared. Considering the viscoelastic damping mechanism, the viscoelastic damping mechanism is modeled based on the integral constitutive form, which is recast into an incremental form suitable for finite element implementation. Additionally, the revolute joint element is adopted to incorporate the joint flexibility in the double wishbone system. The plane frame element is adopted to model the suspension links by using Timoshenko beam theory. The developed nonlinear finite element equations of motion are solved through the incremental iterative Newmark technique. The developed procedure is verified by comparing the obtained results with analytical solution and excellent agreement is observed. The applicability of the developed procedure is demonstrated by conducting parametric studies to show the effects of the road irregularities profiles, the vehicle speed, and the material damping coefficients on the nonlinear vibrations response of the double wishbone suspension systems. The obtained results are supportive in the design and manufacturing processes of these structural systems.

Research paper thumbnail of Finite Element Analysis of Double Wishbone Vehicle Suspension System

Egyptian Journal for Engineering Sciences and Technology, 2019

Suspension systems play an important role in vehicles. These systems provide passenger comfort an... more Suspension systems play an important role in vehicles. These systems provide passenger comfort and vibration isolation from road bumps. Thus an efficient finite element model is required to study and analyze the dynamic response of these suspension systems. This paper presents a finite element model to analyze the dynamic response of double wishbone vehicle suspension system taking into consideration both links and joints flexibilities. Links are modeled using plane frame element based on Timoshenko beam theory (TBT) kinematic relations. On the other hand, the revolute joint element, developed in ANSYS, is adopted to model joints flexibility.Both internal viscoelastic and external viscous as well as the modal proportional damping models are adopted to simulate the damping effect. The resulting dynamic finite element equations of motion are solved using Newmark numerical technique. The proposed numerical methodology is checked by comparing the obtained results with the developed analytical solution and good agreement is noticed. The applicability of the proposed procedure is demonstrated by operating parametric studies to illustrate the effects of the road irregularity configurations, the vehicle travelling velocity, as well as the material damping on the dynamic response characteristics of the double wishbone suspension system. The obtained results are helpful for the mechanical design of these structural systems.

Research paper thumbnail of Analysis of steady-state frictional rolling contact problems in Schapery–nonlinear viscoelasticity

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2018

In the context of an updated Lagrangian formulation, a computational model is developed for analy... more In the context of an updated Lagrangian formulation, a computational model is developed for analyzing the steady-state frictional rolling contact problems in nonlinear viscoelastic solids. Schapery's nonlinear viscoelastic model is adopted to simulate the viscoelastic behavior. In addition to the material nonlinearity, the model accounts for geometrical nonlinearities, large displacements, and rotations with small strains. To satisfy the steady-state rolling contact condition, a spatially dependent incremental form of the viscoelastic constitutive equations is derived. Consequently, the dependence on the past history of the strain rate in the stress–strain law is expressed in terms of the spatial variation of the strain. The contact conditions are exactly satisfied by employing the Lagrange multiplier approach to enforce the contact constraints. The classical Coulomb's friction law is used to simulate friction. The developed model is verified and compared and good agreement ...

Research paper thumbnail of On Bending of Piezoelectrically Layered Perforated Nanobeams Embedded in an Elastic Foundation with Flexoelectricity

Mathematics

Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural co... more Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural components with flexoelectricity has been considered by many researchers because of the developments of nanotechnology and the applicability of piezoelectric composite nanobeam structures in Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). Therefore, the work investigates the size-dependent electromechanical bending of piezoelectrically layered perforated nanobeams resting on elastic foundations including the flexoelectric effect. Within the framework of the modified nonlocal strain gradient elasticity theory, both the microstructure and nonlocality effects are captured. The governing equilibrium equations including piezoelectric and flexoelectric effects are derived using Hamilton’s principle. Closed forms for the non-classical electromechanical bending profiles are derived. The accuracy of the proposed methodology is verified by comparing the obtained results with the available corresp...

Research paper thumbnail of Improvement of spacecraft structure Dynamic Characteristics by Using Honeycomb Sandwich panels

Egyptian Journal for Engineering Sciences and Technology, 2020

Honeycomb cored structures are considered one of the most efficient composite structures which ar... more Honeycomb cored structures are considered one of the most efficient composite structures which are commonly used in different industrial applications. These structures are characterized by high strength to weight ratio and good impact resistance thus it is suitable for aerospace structures. Structural properties of honeycomb structure depend on its lower, upper skin sheet thickness, the core material thickness, cell dimension, cell angle and foil thickness. Using of honeycomb structure panels in satellite main structure provide the opportunity to reduce satellite mass in significant manner. This study concerns with the static and dynamic performance of honeycomb sandwich panel structures and its applications in spacecraft construction. This work studies the static and dynamics characteristics of a spacecraft structure including an intermediate plate made of two different materials; the first one with an Aluminum intermediate sandwich plate while the second with honeycomb sandwich plate. The obtained results show that the satellite structure supported with honeycomb intermediate plate produces higher value of the fundamental resonant frequencies compared to the corresponding ones in satellite structure with Aluminum intermediate plate which is better for the launch vehicle requirements. Moreover, the spacecraft structure mass was reduced by around 15%.

Research paper thumbnail of A Dynamic Analysis of Randomly Oriented Functionally Graded Carbon Nanotubes/Fiber-Reinforced Composite Laminated Shells with Different Geometries

Mathematics, 2022

The present study demonstrates the free vibration behavior of composite laminated shells reinforc... more The present study demonstrates the free vibration behavior of composite laminated shells reinforced by both randomly oriented single-walled carbon nanotubes (SWCNTs) and functionally graded fibers. The shell structures with different principal radii of curvature are considered, such as cylindrical, spherical, elliptical–paraboloid shell, hyperbolic–paraboloid shell, and plate. The volume fraction of the fibers has a linear variation along the shell thickness from layer to layer, while the volume fraction of CNTs is constant in all shell layers and uniformly distributed. The fiber-reinforced elements are distributed with three functions which are V-distribution, O-distribution, and X-distribution in addition to the uniform distribution. A numerical analysis was carried out systematically to validate the proposed solution. A new analytical solution is presented based on the Galerkin approach for shells and is exploited to illustrate the influence of some factors on the free vibration ...

Research paper thumbnail of Dynamic Analysis of a Piezoelectrically Layered Perforated Nonlocal Strain Gradient Nanobeam with Flexoelectricity

Mathematics

This study presents a mathematical size-dependent model capable of investigating the dynamic beha... more This study presents a mathematical size-dependent model capable of investigating the dynamic behavior of a sandwich perforated nanobeam incorporating the flexoelectricity effect. The nonlocal strain gradient elasticity theory is developed for both continuum mechanics and flexoelectricity. Closed forms of the equivalent perforated geometrical variables are developed. The Hamiltonian principle is exploited to derive the governing equation of motion of the sandwich beam including the flexoelectric effect. Closed forms for the eigen values are derived for different boundary conditions. The accuracy of the developed model is verified by comparing the obtained results with the available published results. Parametric studies are conducted to explore the effects of the perforation parameters, geometric dimensions, nonclassical parameters, flexoelectric parameters, as well as the piezoelectric parameters on the vibration behavior of a piezoelectric perforated sandwich nanobeam. The obtained ...

Research paper thumbnail of Dynamic analysis of nanoscale Timoshenko CNTs based on doublet mechanics under moving load

The European Physical Journal Plus, 2021

The novelty of this article is to investigate the dynamic behavior and response of armchair and z... more The novelty of this article is to investigate the dynamic behavior and response of armchair and zigzag carbon nanotubes (CNTs) under the dynamic moving load using a bottom to up modeling nano-mechanics theory. CNTs are modeled as a Timoshenko beam structure with shear deformation effect, and the size influence of CNTs imposed using the doublet mechanics theory. Hamiltonian principle is used to derive the modified equation of motion and nonclassical boundary conditions of CNTs under moving loads. Analytical Navier method solution for simply supported CNTs beam and Newmark time integration method are developed to predict the response of the structure in time-domain. The proposed model is verified and proved with previously published works for free vibration. Parametric analysis is performed to illustrate the influence of doublet length scale, structures of CNTs, load velocities, and mass of the load on the dynamic responses of CNTs. The proposed model is useful in designing and analyzing of MEMS/NEMS, nano-sensor, and nano-actuator manufactured from CNTs.

Research paper thumbnail of Dynamics of perforated higher order nanobeams subject to moving load using the nonlocal strain gradient theory

Smart Structures and Systems, 2021

The goal of this manuscript is to develop a nonclassical size dependent model to study and analyz... more The goal of this manuscript is to develop a nonclassical size dependent model to study and analyze the dynamic behaviour of the perforated Reddy nanobeam under moving load including the length scale and microstructure effects, that not considered before. The kinematic assumption of the third order shear deformation beam theory in conjunction with modified continuum constitutive equation of nonlocal strain gradient (NLSG) elasticity are proposed to derive the equation of motion of nanobeam included size scale (nonlocal) and microstructure (strain gradient) effects. Mathematical expressions for the equivalent geometrical parameters due to the perforation process of regular squared pattern are developed. Based on the virtual work principle, the governing equations of motion of perforated Reddy nanobeams are derived. Based on Navier's approach, an analytical solution procedure is developed to obtain free and forced vibration response under moving load. The developed methodology is v...

Research paper thumbnail of Effects of viscoelastic bonding layer on performance of piezoelectric actuator attached to elastic structure

Materials Research Express, 2022

In the context of the finite elements analysis, the mechanical performance of viscoelastically bo... more In the context of the finite elements analysis, the mechanical performance of viscoelastically bonded smart structures is investigated and analyzed. Three different models are considered and compared. In the 1st model, the actuator is glued to the host structure. On the other hand, in the two other models the actuator is glued to the bonding layer which is glued to the host structures. To explore the effect of the bonding layer characteristics on the mechanical behavior of the host structure, both elastic and viscoelastic layers are considered. The Prony’s series are utilized to simulate the viscoelastic constitutive response. The mathematical formulation of the coupled problem is presented and the dynamic finite elements equations of motion of the coupled electromechanical systems are introduced. The proposed methodology is verified by comparing the obtained results with the available results in the literature and good consentience is observed. Both static and dynamic vibration beh...

Research paper thumbnail of Modeling and analysis of the transient response of viscoelastic solids

Waves in Random and Complex Media, 2020

In this paper, an incremental finite element model (IFEM) for the transient analysis of viscoelas... more In this paper, an incremental finite element model (IFEM) for the transient analysis of viscoelastic solids is developed. The viscoelastic constitutive response is modeled based on the hereditary integral. Two new incremental constitutive forms suitable for finite element implementation are derived; creep-based (CB) and relaxation-based (RB) and, as a consequent, the difficulties associated with the interconversion from the relaxation modulus to the creep compliance and vice versa are avoided. Creep compliance and relaxation modulus are, respectively, modeled using generalized Kelvin-Voigt model and generalized Wiechert's model. To check the validity, the computational procedure, semi-analytical solution is derived for simple viscoelastic cases using Laplace and inverse Laplace transform techniques. The obtained results from the computational procedure are compared with that obtained from the derived semi-analytical solution. To show the validity and applicability of the developed model, two different applications under different excitation patterns are presented. In each application, the time response for displacements and stresses, especially for the dynamic stress concentration factor for both elastic and viscoelastic analyses are investigated. Moreover, the dissipative recoverable nature of the viscoelastic solids under different loading-unloading excitation patterns is illustrated.

Research paper thumbnail of On bending analysis of perforated microbeams including the microstructure effects

Structural Engineering and Mechanics, 2020

This article presents a nonclassical size dependent model based on the modified couple stress the... more This article presents a nonclassical size dependent model based on the modified couple stress theory to study and analyze the bending behavior of perforated microbeams under different loading patterns. Modified equivalent material and geometrical parameters for perforated beam are presented. The modified couple stress theory with one material length scale parameter is adopted to incorporate the microstructure effect into the governing equations of perforated beam structure. The governing equilibrium equations of the perforated Timoshenko as well as the perforated Euler Bernoulli are developed based on the potential energy minimization principle. The Poisson’s effect is included in the governing equilibrium equations. Regular square perforation configuration is considered. Based on Fourier series expansion, closed forms for the bending deflection and the rotational displacements are obtained for simply supported perforated microbeams. The proposed methodology is validated and compare...

Research paper thumbnail of Bending behavior of squared cutout nanobeams incorporating surface stress effects

Steel and Composite Structures, 2020

In nanosized structures as the surface area to the bulk volume ratio increases the classical cont... more In nanosized structures as the surface area to the bulk volume ratio increases the classical continuum mechanics approaches fails to investigate the mechanical behavior of such structures. In perforated nanobeam structures, more decrease in the bulk volume is obtained due to perforation process thus nonclassical continuum approaches should be employed for reliable investigation of the mechanical behavior these structures. This article introduces an analytical methodology to investigate the size dependent, surface energy, and perforation impacts on the nonclassical bending behavior of regularly squared cutout nanobeam structures for the first time. To do this, geometrical model for both bulk and surface characteristics is developed for regularly squared perforated nanobeams. Based on the proposed geometrical model, the nonclassical Gurtin-Murdoch surface elasticity model is adopted and modified to incorporate the surface energy effects in perforated nanobeams. To investigate the effe...

Research paper thumbnail of Stability of perforated nanobeams incorporating surface energy effects

Steel and Composite Structures, 2020

Research paper thumbnail of Vibration response of symmetric and sigmoid functionally graded beam rested on elastic foundation under moving point mass

Mechanics Based Design of Structures and Machines, 2021

Research paper thumbnail of Dynamics analysis of timoshenko perforated microbeams under moving loads

Engineering with Computers, 2020

This paper aims to present a modified continuum mathematical model capable on investigation of dy... more This paper aims to present a modified continuum mathematical model capable on investigation of dynamic behavior and response of perforated microbeam under the effect of moving mass/load for the first time. A size-dependent finite element model with non-classical shape function is exploited to solve the mathematical model and obtain the dynamic response of perforated Timoshenko microbeams under moving loads. To that end, first, equivalent material and geometrical parameters for perforated beam are developed, based on the regular squared perforation configuration. Second, both the stiffness and mass property matrices including the microstructure effect based on modified couple stress theory and Timoshenko first-order shear beam theory are derived for two-node finite element using new shape function. After that, the interaction between the load and beam is modeed and unified with the equation of motion of the beam incorporating mass inertia effects of moving load. The developed procedure is validated and compared. Effects of perforation parameters, moving load velocities, inertia of mass, and the microstructure size parameter on the dynamic response of perforated microbeam structures have been investigated in a wide context. The achieved results are helpful for the design and production of MEMS structures such as frequency filters, resonators, relay switches, accelerometers and mass flow sensors, with perforation.

Research paper thumbnail of Static bending of perforated nanobeams including surface energy and microstructure effects

Engineering with Computers, 2020

This article aims to present comprehensive model and analytical solution to investigate the stati... more This article aims to present comprehensive model and analytical solution to investigate the static bending behavior of regularly squared cutout perforated thin/thick nanobeams incorporating the coupled effect of the microstructure and surface energy for the first time. The perforation influence is considered to be deriving equivalent geometrical and material characteristics. The modified couple stress theory is adopted to incorporate the microstructure effect while the modified Gurtin-Murdoch surface elasticity model is employed to incorporate the surface stress effect in perforated nanobeams. A variational formulation based on minimization of the total potential energy principle is employed to derive the equilibrium equations of perforated nanobeams based on both Euler-Bernoulli and Timoshenko beams theories are developed to investigate the associated effect of the shear deformation due to perforation process. Additionally, Poisson's effect is also incorporated. Analytical closed-form for the non-classical bending profiles as well as the rotational displacement are developed for both beam theories considering the simultaneous effect of both couple stress and surface stress for both uniformly distributed and concentrated loading patterns. The verification of the developed model is verified and compared with previous works, and an excellent agreement is obtained. The applicability of the developed model is demonstrated and applied to study and analyze the nonclassical bending behavior of regularly squared perforated simply supported beams under different loading conditions. Additionally, effects of the perforation configuration parameters, beam size as well as beam aspect ratio on the bending behavior of perforated beams in the presence of microstructure and surface stress effects are also investigated and analyzed. The obtained results reveal that both couple stress and surface stress significantly affect the bending behavior of regularly squared cutout perforated beam structures. Results obtained are supportive for the design, analysis and manufacturing of perforated NEMS applications.

Research paper thumbnail of Influence of the perforation configuration on dynamic behaviors of multilayered beam structure

Structures, 2020

The novelty of this paper is to investigates the free vibration, frequency response and modal par... more The novelty of this paper is to investigates the free vibration, frequency response and modal participation factors of the perforated multilayer microbeam structures using finite element analysis with different hole's geometry, filling ratio and array of hole. The three squared, rectangular, and circular configurations of perforation are considered through analysis. Elasto-dynamic finite element formulation is implemented. The natural frequencies for the three different perforation configurations at different number of holes are investigated. For better understanding of the dynamic behavior of multilayered perforated beam structure, both modal and harmonic responses are presented and discussed. To specify the most suitable vibrational mode for a certain degree of freedom for base excitation, both participation factor and the associated modal effective mass are presented and analyzed. The obtained results show the remarkable effect of perforation configuration and the number of holes throughout the cross-sectional area on the dynamic behavior of multilayered perforated beam structures. Different boundary conditions are considered through analysis. The obtained results are supportive for the design of perforated beam structures in both macro and micro-scales.

Research paper thumbnail of Dynamics of perforated nanobeams subject to moving mass using the nonlocal strain gradient theory

Applied Mathematical Modelling, 2021

Abstract In the present manuscript, based on the nonlocal strain gradient theory, a nonclassical ... more Abstract In the present manuscript, based on the nonlocal strain gradient theory, a nonclassical dynamic finite element model is developed to study and analyze the dynamic behavior of perforated nanobeam structures under moving mass/load. In the context of nonclassical continuum mechanics and Timoshenko beam theory, dynamic equations of motion of perforated nanobeams are derived including both size scale (nonlocal) and microstructure (strain gradient) effects. The modification of the geometrical parameters due to the perforation process is included in the equations of motion for squared holes arranged in the arrayed form. The effect of the moving mass (the inertia, Coriolis and centripetal forces, and the gravity force) or moving load are included in the proposed model. To remove shear locking problem in slender nanobeams, finite element model on nonclassical shape function basis is developed. Elements stiffness and mass matrices and force vector including the nonlocal and strain gradient effects are derived. The proposed model is verified and checked with previous works. Impacts of perforation, mass/load velocities, inertia of mass, microstructure parameter and nonlocal size scale effects on the dynamic and vibration responses of perforated nanobeam structures have been investigated in a wide context. The following model is beneficial for the design of MEMS/NEMS structures such as frequency filters, resonators, relay switches, accelerometers, and mass flow sensors, with perforation.

Research paper thumbnail of Vibration response of Timoshenko perforated microbeams under accelerating load and thermal environment

Applied Mathematics and Computation, 2021

Research paper thumbnail of Nonlinear dynamics of viscoelastic flexible structural systems by finite element method

Engineering with Computers, 2020

This article presents a nonlinear displacement based finite elements model to study and analyze t... more This article presents a nonlinear displacement based finite elements model to study and analyze the nonlinear dynamic response of flexible double wishbone structural vehicle suspension system considering damping effect which was not previously discussed elsewhere. Due to large deflection and moderate rotation encountered during passing over road bumps, the kinematic nonlinearity is included through von Kármán strain component. Elastic undamped as well as viscous and viscoelastic damping mechanism are considered and compared. Considering the viscoelastic damping mechanism, the viscoelastic damping mechanism is modeled based on the integral constitutive form, which is recast into an incremental form suitable for finite element implementation. Additionally, the revolute joint element is adopted to incorporate the joint flexibility in the double wishbone system. The plane frame element is adopted to model the suspension links by using Timoshenko beam theory. The developed nonlinear finite element equations of motion are solved through the incremental iterative Newmark technique. The developed procedure is verified by comparing the obtained results with analytical solution and excellent agreement is observed. The applicability of the developed procedure is demonstrated by conducting parametric studies to show the effects of the road irregularities profiles, the vehicle speed, and the material damping coefficients on the nonlinear vibrations response of the double wishbone suspension systems. The obtained results are supportive in the design and manufacturing processes of these structural systems.

Research paper thumbnail of Finite Element Analysis of Double Wishbone Vehicle Suspension System

Egyptian Journal for Engineering Sciences and Technology, 2019

Suspension systems play an important role in vehicles. These systems provide passenger comfort an... more Suspension systems play an important role in vehicles. These systems provide passenger comfort and vibration isolation from road bumps. Thus an efficient finite element model is required to study and analyze the dynamic response of these suspension systems. This paper presents a finite element model to analyze the dynamic response of double wishbone vehicle suspension system taking into consideration both links and joints flexibilities. Links are modeled using plane frame element based on Timoshenko beam theory (TBT) kinematic relations. On the other hand, the revolute joint element, developed in ANSYS, is adopted to model joints flexibility.Both internal viscoelastic and external viscous as well as the modal proportional damping models are adopted to simulate the damping effect. The resulting dynamic finite element equations of motion are solved using Newmark numerical technique. The proposed numerical methodology is checked by comparing the obtained results with the developed analytical solution and good agreement is noticed. The applicability of the proposed procedure is demonstrated by operating parametric studies to illustrate the effects of the road irregularity configurations, the vehicle travelling velocity, as well as the material damping on the dynamic response characteristics of the double wishbone suspension system. The obtained results are helpful for the mechanical design of these structural systems.

Research paper thumbnail of Analysis of steady-state frictional rolling contact problems in Schapery–nonlinear viscoelasticity

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2018

In the context of an updated Lagrangian formulation, a computational model is developed for analy... more In the context of an updated Lagrangian formulation, a computational model is developed for analyzing the steady-state frictional rolling contact problems in nonlinear viscoelastic solids. Schapery's nonlinear viscoelastic model is adopted to simulate the viscoelastic behavior. In addition to the material nonlinearity, the model accounts for geometrical nonlinearities, large displacements, and rotations with small strains. To satisfy the steady-state rolling contact condition, a spatially dependent incremental form of the viscoelastic constitutive equations is derived. Consequently, the dependence on the past history of the strain rate in the stress–strain law is expressed in terms of the spatial variation of the strain. The contact conditions are exactly satisfied by employing the Lagrange multiplier approach to enforce the contact constraints. The classical Coulomb's friction law is used to simulate friction. The developed model is verified and compared and good agreement ...