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The enormous increase in the application of nano-electromechanical systems for biological purposes, as well as modern sensors in the particle accelerators, leads to new operation situations for these devices, such as an external magnetic field. While different physical phenomena on the behavior of nano-electromechanical systems have been addressed, few researchers have focused on the magnetic flux’s inspiration on the performance of electromechanical nano-sensors. In this paper, the dynamic electromagnetic instability of nano-sensors immersed in an external magnetic flux is simulated. As nano-structures have a considerable surface-to-volume ratio, the constitutive equation is developed by incorporating surface energies. The impact of finite dimensions is taken into account in the developed model by using corrected relations for electrical and van der Waals force. The nonlinear dynamic behavior of the system is investigated by employing the Galerkin method. We find that the magnetic flux can significantly reduce the dynamic instability threshold of the nano-sensors.

Today, many scientists, as well as researchers, have devoted themselves to the quest of micro and nanoelectromechanical system (NEMS/MEMS) technologies because of their extraordinary potential in the field of fundamental research and application in industrial engineering. In-depth knowledge of MEMS and NEMS under various physical phenomena can significantly reduce the time and cost of designing, developing, and optimizing of the nanostructures compared with repeated fabrication and testing in the laboratory. In this section, the essential concepts for modeling ultrasmall structures are introduced, and the physical phenomena appearing on the nano- and microscale are discussed.

Novel developments in modern computers have simplified the application of mathematical methods for modeling and simulation of physical phenomena. Continuum mechanics is one of the most popular ways for simulating micro- and nanostructures that do not require computational equipment such as molecular dynamics. Moreover, their results are more accurate compared to simple approaches. However, continuum mechanics usually leads to highly-nonlinear differential equations so that a precise solution cannot be found for them. In this chapter, a variety of numerical approaches to solve the nonlinear differential equations are introduced, and the behavior of some micro- and nanostructures are investigated according to these methods.

Experiments depict that the physico-mechanical response of miniature devices is microstructure-dependent. However, the classic continuum theory cannot correctly predict the microstructure-dependency. In this paper, the strain gradient theory is employed to examine the dynamic behavior and instability characteristics of miniature varactor with trapezoidal geometry. The governing equation of the varactor is obtained incorporating the effects of Coulomb force, van der Waals (vdW) attraction, squeeze film damping and structural damping. The influences of microstructure on the dynamic instability of equilibrium points are studied by plotting the phase portrait and bifurcation diagrams. It is found that increase in the microstructure parameter enhances the torsional stability. In the presence of the applied voltage, the phase portrait shows the saddle-node bifurcation while for free-standing varactor a subcritical pitchfork bifurcation is observed.

The present research is devoted to theoretical study of the pull-in performance of double-sided and paddle-type NEMS actuators fabricated from cylindrical nanowire operating in the Casimir regime and in the presence of the centrifugal force. D'Alembert's principle was used to transform the angular velocity into an equivalent static, centrifugal force. Using the couple stress theory, the constitutive equations of the actuators were derived. The equivalent boundary condition technique was applied to obtain the governing equation of the paddle-type actuator. Three distinct approaches, the Duan-Adomian Method (DAM), Finite Difference Method (FDM), and Lumped Parameter Model (LPM), were applied to solve the equation of motion of these two actuators. This study demonstrates the influence of various parameters, i.e., the Casimir force, geometric characteristics, and the angular speed, on the pull-in performance. (C) 2017 Sharif University of Technology. All rights reserved.

A mathematical model is used to study the effects of the electrostatic, Casimir and centrifugal forces on the static behaviors of the two U-shaped NEMS with rectangular and circular geometries. The size-dependent equations are obtained by employing the consistent couple stress theory (CCST). The D’Alembert principle is used to transform the angular speed into an equivalent static centrifugal force. The equivalent boundary condition technique is applied for obtaining the governing equation of the U-shape actuator. The nonlinear equations are solved by two different approaches, i.e., using a distributed parameter model (in conjunction with Rayleigh–Ritz solution method) and a lumped parameter model. The model is validated by comparing the obtained results with those of experiment as well as finite element simulation. The effect of various parameters on the instability threshold and characteristics of the system is discussed. The obtained results are beneficial for design and fabrication of U-shaped sensors.

It has been well-established that the physical performance of nano-devices might be affected by the microstructure. Herein, a 2 degree-of-freedom model based on modified couple stress elasticity is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nano-scanner. The governing equation of the varactor is derived incorporating the effects of electrostatic Coulomb and corrected Casimir forces with the consideration of the finite conductivity of interacting surfaces. Effect of microstructure-dependency on the instability parameters are determined as a function of the microstructure parameter, bending/torsion coupling ratio, vacuum fluctuation parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the scanners especially those with long rotational beam elements. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to size phenomenon) and softening behavior (due to torsion/bending coupling) of the nano-mirror.

In this research, rubber based nanocomposites with presence of nanoparticle has been studied. Styrene butadiene rubber (SBR)/nanocopper (NC) composites were prepared using two-roll mill method. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images showed proper dispersion of NC in the SBR matrix without substantial agglomeration of nanoparticles. To evaluate the curing properties of nanocomposite samples, swelling and cure rheometric tests were conducted. Moreover, the rheological studies were carried out over a range of shear rates. The effect of NC particles was examined on the thermal behavior of the SBR using thermal gravimetric analysis (TGA). Furthermore, tensile tests were employed to investigate the capability of nanoparticles to enhance mechanical behavior of the compounds. The results showed enhancement in tensile properties with incorporation of NC to SBR matrix. Moreover, addition of NC increased shear viscosity and curing time of SBR composites. Keywords: Nanocopper, Rubber, Curing behavior, Rheological properties, Thermal stability, Tensile characteristics

The external magnetic field might affect the performances of electromechanical nano-bridges sensors and switches. While different physical phenomena on the behavior of nano-electromechanical systems have been addressed, few works have been done on the inspiration of the magnetic flux on the performance of these systems. Herein, the primary field equations necessary for dynamic instability analysis of electromechanical nano-bridges subjected to an external magnetic flux are extracted. The simultaneous effects of scale dependency and surface energies are considered in the proposed. To this end, the consistent couple stress theory is incorporated with the surface elasticity. Next, the system’s nonlinearity is defined by using von-Karman nonlinear strains. Also, the impact of vacuum fluctuation is also considered in the developed model. A reduced-order procedure is designed to solve the constitutive equation, and the effects of the longitudinal magnetic field on the instability of nano-bridge are examined. The outcomes demonstrate that the longitudinal magnetic flux considerably increases the instability voltage of the nano-bridge.

Paddle-type and double-sided nanostructures have much potential for measuring the angular speed in rotary systems and aerospace applications. While most investigations in the literature have concentrated on the electromechanical performance of conventional beam-type nanostructures, few researchers have addressed the performance of these systems. The pull-in instability of the cantilever paddle-type and double-sided sensors in the presence of the centrifugal force have been investigated. The nonlinear governing equations are solved and the obtained results are compared with the numerical solution. The influences of the van der Waals force, geometric parameters, angular speed, and size phenomenon on the instability performance have been demonstrated.

For modeling the electromechanical behavior of nano-bridge structures with slender narrow-width beam elements, not only the simultaneous effects of surface layer and size dependency should be taken into account but also corrected force models should be considered. In this paper, the instability of a narrow-width nano-bridge is studied based on strain gradient theory and Gurtin–Murdoch surface elasticity. The mid-plane stretching is incorporated in the governing equation as well as corrected force distribution. Using Rayleigh–Ritz method, a parametric analysis is conducted to examine the impacts of surface layer, size dependence, dispersion forces and structural damping on static and dynamic instability voltage of the nano-bridge.

It has been well-established that the physical performance of nano-devices might be affected by the microstructure. Herein, a 2-degree-of-freedom model based on the modified couple stress elasticity is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nano-electromechanical mirror. The governing equation of the mirror is derived incorporating the effects of electrostatic Coulomb and corrected Casimir forces with the consideration of the finite conductivity of interacting surfaces. Effect of microstructure-dependency on the instability parameters are determined as a function of the microstructure parameter, bending/torsion coupling ratio, vacuum fluctuation parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the mirrors especially those with long rotational beam elements. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nano-mirror.

Nano-scale beams might not be considered uniform isotropic since the energy of the surface layer and microstructure of the bulk part highly affect the mechanical characteristics of the beams. Herein, the impact of the energy of the surface layer and the microstructure of the bulk on the mechanical stability of beam-type nanotweezers are investigated. A new bilayer continuum model has been developed which incorporates the strain energy of the surface atoms as well as the microstructure-dependent strain energy of the bulk material. The recently-developed consistent couple stress elasticity (CCSE) in combination with the Gurtin-Murdoch surface theory is applied to derive the governing equation. The nonlinear governing equation was solved using numerical generalized differential quadrature (GDQ). Effects of various parameters including characteristics of the surface layer, microstructure of the bulk and external forces on the static and dynamic stability threshold of the nanostructure are demonstrated.

Surface energy and microstructure-dependent size phenomena can play significant roles in physical performance of nanoelectromechanical systems (NEMS). Herein, the static and dynamic pull-in instability of cantilever and double-clamped NEMS fabricated from conductive cylindrical nanowires with circular cross section is studied. The Gurtin–Murdoch surface elasticity in combination with the couple stress continuum theory is employed to incorporate the coupled effects of surface energy and microstructure-dependent size phenomenon. Using Green–Lagrange strain, the higher order surface stress components are incorporated into the governing equation. The effect of gas damping is considered in the model as well as structural damping. The nonlinear governing equation is solved using analytical reduced order method. The effects of various parameters on the static and dynamic pull-in parameters, phase plans, and stability threshold of the nanowire-based structures are demonstrated.

A nonlinear beam formulation is presented based on the Gurtin-Murdoch surface elasticity and the modified couple stress theory. The developed model theoretically takes into account coupled effects of the energy of surface layer and microstructures sizedependency. The mid-plane stretching of a beam is incorporated using von-Karman nonlinear strains. Hamilton’s principle is used to determine the nonlinear governing equation of motion and the corresponding boundary conditions. As a case study, pull-in instability of an electromechanical nano-bridge structure is studied using the proposed formulation. The nonlinear governing equation is solved by the analytical reduced order method (ROM) as well as the numerical solution. Effects of various parameters including surface layer, size dependency, dispersion forces, and structural damping on the pullin parameters of the nano-bridges are discussed. Comparison of the results with the literature reveals capability of the present model in demonstrating the impact of nanoscale phenomena on the pull-in threshold of the nano-bridges.

Surface energy and size phenomenon can play significant roles in physical performance of nano-electromechanical systems. Herein, the static and dynamic pull-in behavior of nano-tweezers and nano-switch fabricated from conductive cylindrical nano-wires is studied. The Gurtin–Murdoch surface elasticity in combination with the couple stress theory is employed to incorporate the coupled effects of surface energy and microstructure dependency (size phenomenon). Using Green–Lagrange strain, the higher-order surface stress components are incorporated in the nonlinear governing equation. The effect of gas damping is considered in the model as well as structural damping. The governing equation is solved using the reduced order method. The effects of various parameters on the static and dynamic pull-in parameters, phase plans and stability threshold of the nano-structures are demonstrated.

While comprehensive researches have been conducted on modeling the electromechanical stability of wide-enough beam-plate nano-switches, few researchers have focused on modeling the electromechanical instability of narrow-width nano-switches. For such systems, considering the coupled effects of surface stresses and size dependency of material characteristics is crucial as well as applying appropriate force models. In this paper, Gurtin–Murdoch surface theory incorporating with strain gradient elasticity is employed to study the pull-in instability of narrow-width beam-type nano-switch with small width to height ratio. The model accounts for the force corrections, i.e. the impact of finite dimensions on the fringing field, Casimir attraction and van der Waals force. Furthermore, a modified gas damping model has been incorporated in the governing equation. The nonlinear governing equation was solved using analytical Rayleigh–Ritz method. The influences of the above-mentioned corrections on the static and dynamic pull-in parameters, phase planes and stability threshold of the switch are demonstrated. The modified model is compared with conventional parallel beam-plate models in the literature.

Surface energy and size phenomenon can highly affect the physical performance of ultra-small systems. Herein, the static and dynamic stability of nanotweezers fabricated from conductive cylindrical nanowires is studied under the presence of Casimir force. The Gurtin---Murdoch surface elasticity in combination with the consistent couple stress theory is employed to incorporate the coupled effects of surface energy and size phenomenon. Using Green---Lagrange strain, the higher order surface stress components are incorporated in the governing equation. The Dirichlet mode is considered and an asymptotic solution, based on the path integral approach, is applied to consider the effect of the Casimir attraction. Numerical generalized differential quadrature is employed to solve the nonlinear governing equation of system. The effects of various parameters on the static and dynamic pull-in parameters and stability threshold of the tweezers are demonstrated.

The U-shaped and double-sided nanostructures are promising for developing miniature angular speed sensors. While the electromechanical instability of conventional beam-type nanostructures has been extensively addressed in the literature, few researchers have investigated this phenomenon in the double-sided and U-shaped sensors. In this regard, the present work demonstrates the effect of the centrifugal force on the pull-in performance of the double-sided and U-shaped sensors fabricated from cylindrical nanowire and operated in the van der Waals (vdW) regime. Based on the modified couple stress theory, the size-dependent constitutive equations of the sensors are derived. The governing equations are solved by two different approaches, i.e. the analytic Duan–Adomian method and the numerical differential quadrature method. The influences of the vdW and centrifugal forces, geometric parameters and the size phenomenon on the pull-in parameters are demonstrated.

For the case of micro/nano-scale structures, it is well-known that the physico-mechanical behavior of such devices is size-dependent. However, the classical continuum theory cannot correctly predict the size-dependency. In this paper, the modified couple stress theory is employed to examine the instability characteristics of scanner-type nano-mirrors with circular geometry. The governing equation of the scanner is derived incorporating the effects of electrostatic Coulomb and corrected Casimir forces with the consideration of the finite conductivity of interacting surfaces. In addition, to investigate the influence of air damping, a modified nonlinear expression for the squeeze film model is proposed. The influences of vacuum fluctuation, applied voltage, nonlinear damping and length scale parameter on the dynamic instability of equilibrium points are studied by plotting the phase portrait and bifurcation diagrams. It is concluded from the obtained results that the Casimir attraction reduces the instability threshold of the nano-systems. The small-scale parameter and the nonlinear squeeze film damping enhance the torsional stability. In the presence of the applied voltage, the phase portrait shows the saddle-node bifurcation while for free-standing scanner a subcritical pitchfork bifurcation is observed.

Herein, the dynamic pull-in instability of cantilever nanoactuator fabricated from conductive cylindrical nanowire with circular cross-section is studied under the presence of Casimir force. The Gurtin–Murdoch surface elasticity in combination with the couple stress theory is employed to incorporate the coupled effects of surface energy and size phenomenon. Using Green–Lagrange strain, the higher order surface stress components are incorporated in the governing equation. The Dirichlet mode is considered and an asymptotic solution, based on the path integral approach, is applied to consider the effect of the Casimir attraction. Furthermore, the influence of structural damping is considered in the model. The nonlinear governing equation is solved using analytical reduced order method (ROM). The effects of various parameters on the dynamic pull-in parameters, phase planes and stability threshold of the actuator are demonstrated.

Paddle-type and double-sided nanostructures are potential for use as accelerometers in flying vehicles and aerospace applications. Herein the pull-in instability of the cantilever paddle-type and double-sided sensors in the Casimir regime are investigated under the acceleration. The D׳Alembert principle is employed to transform the accelerating system into an equivalent static system by incorporating the accelerating force. Based on the couple stress theory (CST), the size-dependent constitutive equations of the sensors are derived. The governing nonlinear equations are solved by two approaches, i.e. modified variational iteration method and finite difference method. The influences of the Casimir force, geometrical parameters, acceleration and the size phenomenon on the instability performance have been demonstrated. The obtained results are beneficial to design and fabricate paddle-type and double-sided accelerometers.

Finite conductivity, surface energy and nonlocal effect can influence the electromechanical performance of micro/nano-electromechanical systems (MEMS/NEMS). However, these factors are yet ignored on stability analysis of MEMS/NEMS fabricated from functionally graded materials (FGM). In this paper, dynamic stability of double-sided NEMS fabricated from non-symmetric FGM is investigated incorporating finite conductivity, surface energy and nonlocal effect. The Gurtin–Murdoch model and Eringen's elasticity are employed to consider the surface energy and nonlocal effect, respectively. Effect of finite conductivity of FGM on electrostatic and Casimir attractions is incorporated via relative permittivity and plasma frequency of the material. The stability analysis of the nanostructure is conducted by plotting time history and phase portraits. Moreover, bifurcation analysis is conducted to investigate the stability of the fixed points of the nano-structure. The validity of the proposed model is examined by comparing the results of the present study with those reported in the literature. The impact of various parameters i.e. finite conductivity, nonlocal parameter, surface stresses and material characteristics on the dynamic instability of the NEMS are addressed.

Double-sided electromechanical nano-bridges can potentially be used as angular speed sensors and accelerometers in rotary systems such as turbine blades and vacuum pumps. In such applications, the influences of the centrifugal force and rarefied flow should be considered in the analysis. In the present study, the non-linear dynamic pull-in instability of a double-sided nano-bridge is investigated incorporating the effects of angular velocity and rarefied gas damping. The non-linear governing equation of the nanostructure is derived using Euler-beam model and Hamilton׳s principle including the dispersion forces. The strain gradient elasticity theory is used for modeling the size-dependent behavior of the system. The reduced order method is also implemented to discretize and solve the partial differential equation of motion. The influences of damping, centrifugal force, length scale parameters, van der Waals force and Casimir attraction on the dynamic pull-in voltage are studied. It is found that the dispersion and centrifugal forces decrease the pull-in voltage of a nano-bridge. Dynamic response of the nano-bridge is investigated by plotting time history and phase portrait of the system. The validity of the proposed method is confirmed by comparing the results from the present study with the experimental and numerical results reported in the literature.

While vinyl-terminated butadiene acrylonitrile is frequently used for the toughening of vinylester and polyester, very limited research has been conducted on modification of epoxy with this oligomer. Herein, the effect of vinyl-terminated butadiene acrylonitrile addition to epoxy in bulk and glass reinforced composite is systematically investigated. Thermo-physical behavior and mechanical characteristics of the samples are determined. To interpret the test results, the void content of reinforced samples is measured and fracture surface of the specimens is investigated. It is found that vinyl-terminated butadiene acrylonitrile improves the toughness with slight negligible effects on other characteristics. Incorporation of 15 phr of vinyl-terminated butadiene acrylonitrile increases the KIC of epoxy from 0.6 MPa to 2.3 MPam0.5. Similarly, addition of 15 phr vinyl-terminated butadiene acrylonitrile leads to 67% enhancement in the interlaminar fracture toughness of composites. The toughening mechanism...

While few studies have been conducted on modeling the pull-in instability of cantilever nanoelectromechanical systems (NEMS) in electrolyte media, no researchers has investigated this phenomenon in double-clamped NEMS. Herein, the pull-in instability of the NEMS bridge immersed in ionic liquid electrolyte media is explored for the first time considering the size effect and dispersion forces. The strain gradient elasticity in conjunction with von-Karman strain is employed to incorporate the effect of size-dependency and beam stretching in the structural model. The presence of electrochemical force field and nano-scale attractions i.e. Casimir and van der Waals forces is incorporated in the model considering the presence of the liquid media. To solve the nonlinear constitutive equation of the system two different methods including the differential transformation method (DTM) and numerical solution are employed. The proposed model is validated by comparing with the results presented in literature. Impacts of various parameters i.e. the size dependency, dispersion forces, electrolyte ion concentration and potential ratio on the instability characteristics of the NEMS bridge are discussed. The results of present theory are compared with those predicted by the classic continuum theory as well as the modified couple stress theory.

Finite conductivity, size dependency and surface layer are known as crucial factors that affect the electromechanical response and pull-in instability of micro/nano-electromechanical systems (MEMS/NEMS). However, these effects are yet ignored on modeling the instability of MEMS/NEMS fabricated from functionally graded materials (FGMs). Herein, a modified continuum model is developed to incorporate these effects on the dynamic behavior and electromechanical instability of double-sided FGM NEMS bridge. Using Gurtin–Murdoch model in conjunction with nonlocal Eringen elasticity, the governing equations of the nano-bridges is derived considering the surface layer and size dependency. The Coulomb and Casimir forces are incorporated in the governing equation considering the corrections due to the finite conductivity of FGM (relative permittivity and plasma frequency). The validity of the proposed method is elucidated by comparing the results obtained from the present study with the results reported in the literature. The stability analysis of the nanostructure is conducted by plotting time history and phase portraits. The effects of various parameters including finite conductivity, nonlocal parameter, surface stresses and material characteristics on the dynamic pull-in behavior of the nano-bridges are studied. The obtained results imply a significant impact of the abovementioned corrections on the instability threshold and pull-in parameters of the FGM nanobridge.

In this paper, the electromechanical response and instability of the nanobridge immersed in ionic electrolyte media is investigated. The electrochemical force field is determined using double-layer theory and linearized Poisson–Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions are incorporated considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). The strain gradient elasticity is employed to model the size-dependent structural behavior of the nanobridge. To solve the nonlinear constitutive equation of the system, three approaches, e.g., the Rayleigh–Ritz method, Lumped parameter model and the numerical solution method are employed. Impacts of the dispersion forces and size effect on the instability characteristics as well as the effects of ion concentration and potential ratio are discussed.

While the pull-in instability of beam-type electromechanical nanoactuators with single actuating electrode has been widely addressed in literature, limited research works have been devoted to modeling the pull-in phenomenon in actuators with double-sided actuating electrodes. Herein, couple stress theory (CST) has been used to study the size-dependent instability of two double-sided actuators, i.e., nano-bridges and nano-cantilevers. The influence of Casimir force has been considered in the model. The analytical differential transformation method (DTM) has been applied to solve the governing equations as well as numerical method. Furthermore, a lumped parameter model has been developed to simply explain the physical performance of the systems without mathematical complexity. The critical deflection and pull-in voltage of the nanostructures as basic design parameters have been calculated. Effect of the Casimir attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed for both nano-structures. The present work can be helpful to precise design and analysis of nano-cantilevers and nano-bridges.

Experimental observations reveal that the physical response of nano-structures is size-dependent. Herein, modified strain gradient theory in conjunction with Euler–Bernoulli beam theory have been used for mathematical modeling of the size dependent instability of nanostructures. Effect of van der Waals intermolecular force has been included in the mathematical model. Two common beam-type systems including double-clamped nano-bridge and clamped-free nano-cantilever have been investigated. Three approaches including using an approximated differential transformation method (DTM), applying iterative numerical method and developing a simple lumped parameter model have been employed to solve the governing equations of the systems. The obtained results have been compared with those obtained via numerical method. Furthermore a lumped parameter model has been developed to simply explain the physical performance of the systems without mathematical complexity. The pull-in parameters of the nanostructures as basic design parameters have been calculated. Effect of the size dependency on the pull-in performance has been discussed for both nano-structures.

Toughening of epoxy with different types of modifiers produces a bimodal blend that might show better fracture resistance in comparison with single-modified ones. In this research, bimodal epoxy formulations including mixtures of glass microsphere and silica nanoparticles are explored for possible synergistic toughening. The influence of composition on the glass transition temperature ( Tg), tensile characteristics, and fracture toughness ( KIC) is investigated. Interestingly, a synergism in fracture toughness is observed when mixtures of modifiers were incorporated. For the fixed overall modifier content, KIC is higher when the volume fraction of glass microsphere is lesser than the volume fraction of nanosilica. Fractographs reveal that glass microsphere increases the toughness of epoxy matrix by crack pinning/bridging mechanisms. On the other hand, nanosilica enhances the toughness by increase in plastic deformation via shear banding/particle debonding. Interestingly, the origin of synergistic toughness in bimodal epoxies is the interaction between the glass microsphere and crack-tip damage zone which provides comprehensive stable crack deflection within the nanosilica-toughened epoxy. This mechanism results in a mixed-mode crack growth that reduces the strain energy release rate in bimodal formulations.

In this research the effects of surface quality and loading history on fatigue behavior of CO 2 laser-machined poly(methyl methacrylate) are investigated. It is found that polishing of laser-machined surfaces can enhance the tensile strength up to 5% while significantly elongating the fatigue life of specimens. Microscopic observations reveal that defects on lateral laser machined surface and heat affected zone lead to a reduction of fatigue life by a factor of ten compared to samples with polished lateral surfaces. In the second part of this research it is observed that the loading sequence has a definite effect on the remaining life of poly(methyl methacrylate). Finally the ability of several cumulative damage formulations for modeling the fatigue life in multi-stage loading is evaluated, out of which Manson–Halford and Otani–Song models outperformed the others.

Herein, the fracture toughness of ternary epoxy systems containing nanosilica and hollow glass microspheres (HGMS) is investigated. The experimental measurements reveal synergistic fracture toughness in some hybrid compositions: The incorporation of 10 phr of HGMS and nanosilica alone modify the fracture toughness of epoxy by 39% and 91%, respectively. However, use of 10 phr hybrid modifier can enhance the fracture toughness of the resin up to 120%. Observations reveal different toughening mechanisms for the blends i.e., plastic deformation for silica nanoparticles and crack bifurcation for HGMS. Both of these toughening mechanisms additively contribute to the synergism in ternary epoxies.

In this paper, the impact of the Casimir attraction on the electromechanical stability of nanowire-fabricated nanotweezers is investigated using a theoretical continuum mechanics model. The Dirichlet mode is considered and an asymptotic solution, based on path integral approach, is applied to consider the effect of vacuum fluctuations in the model. The Euler-Bernoulli beam theory is employed to derive the nonlinear governing equation of the nanotweezers. The governing equations are solved by three different approaches, i.e. the modified variation iteration method, generalized differential quadrature method and using a lumped parameter model. Various perspectives of the problem, including the comparison with the van der Waals force regime, the variation of instability parameters and effects of geometry are addressed in present paper. The proposed approach is beneficial for the precise determination of the electrostatic response of the nanotweezers in the presence of Casimir force.

It is well-recognized that the electromechanical response of a nanostructure is affected by its element size. In the present article, the size dependent stability behavior and nanotweezers fabricated from nanowires are investigated by modified couple stress elasticity (MCSE). The governing equation of the nanotweezers is obtained by taking into account the presence of Coulomb and intermolecular attractions. To solve the equation, four techniques, i.e., the modified variational iteration method (MVIM), the monotonic iteration method (MIM), the MAPLE numerical solver, and a lumped model, are used. The variations of the arm displacement of the tweezers versus direct current (DC) voltage are obtained. The instability parameters, i.e., pull-in voltage and deflection of the system, are computed. The results show that size-dependency will affect the stability of the nanotweezers significantly if the diameter of the nanowire is of the order of the length scale. The impact of intermolecular attraction on the size-dependent stability of the system is discussed.

Experimental observations reveal that the physical response of nanostructures is size-dependent. Herein, modified couple stress theory has been used to study the effect of intermolecular van der Waals force on the size dependent pull-in of nanobridges and nanocantilevers. Three approaches including using differential transformation method, applying numerical method and developing a simple lumped parameter model have been employed to solve the governing equation of the systems. The pull-in parameters i.e. critical tip deflection and instability voltage of the nanostructures have been determined. Effect of the van der Waals attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed.

The Casimir force can induce instability and adhesion in freestanding nanostructures. Previous research efforts in this area have exclusively focused on modeling the instability in structures with planar or rectangular cross-section, while, to the best knowledge of the authors, no attention has been paid to investigate this phenomenon for nanowires with circular cross-section. In this study, effects of the Casimir force on the instability and adhesion of freestanding Cylinder–Plate and Cylinder–Cylinder geometries are investigated, which are commonly encountered in real nanodevices. To compute the Casimir force, two approaches, i.e. the proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation (scattering theory) for large separations, are considered. A continuum mechanics theory is employed, in conjunction with the Euler-beam model, to obtain constitutive equations of the systems. The governing nonlinear constitutive equations of the nanostructures are solved using two different approaches, i.e. the analytical modified Adomian decomposition (MAD) and the numerical finite difference method (FDM). The detachment length and minimum gap, both of which prevent the Casimir force-induced adhesion, are computed for both configurations.

In recent years, carbon nanotubes (CNTs) have attracted great attention in the fabrication of probe tips and actuators for scanning microscopes. Herein, the pull-in instability of CNT-based probe is investigated using a nanoscale continuum model. The Euler–Bernoulli beam theory is applied to model the elastic response of the CNT. The van der Waals attraction is computed from the simplified Lennard-Jones potential. Two analytical methods (i.e., Homotopy perturbation method and Adomian decomposition method) are applied to solve the nonlinear governing equation of the system. Furthermore, the obtained results are validated by comparing with experimental results in the literature as well as numerical solutions of the finite difference method. The pull-in parameters are determined and effect of van der Waals force and a geometrical parameter effect on the instability behavior of the CNT is discussed. Moreover, the detachment length and minimum initial gap of the freestanding CNT probe are determined.

It is well established that electromechanical response of a nano-electromechanical system (NEMS) might be size-dependent. Herein, the size dependent electrostatic instability of NEMS sensor/actuator fabricated from nano-wires with circular cross-section is theoretically investigated considering the effects of the Coulomb electrostatic and van der Waals molecular attractions. For this purpose, modified couple stress theory is applied to model the size effect on the instability of the system. The van der Waals and Coulomb attractions are computed from the simplified Lennard---Jones potential and the electrical capacitance model, respectively. In order to solve the nonlinear constitutive equation of the system, four different approaches including modified variational iteration method, monotonic iteration method, lumped parameter model and numerical solution are employed. It is found that when the diameter of the nano-wire is comparable with the intrinsic material length scale, size effect can substantially influence the pull-in voltage of the system. Interestingly, a coupling between van der Waals force and size dependency can affect the instability deflection of the sensor/actuator.

It is well-established that mechanical response of nanostructures is size-dependent. In this article, the size-dependent pull-in instability of rotational nano-mirror is investigated using modified couple stress theory. The governing equation of the mirror is derived taking the effect of electrostatic Coulomb and Casimir forces into account. Effect of finite conductivity of material is included in the Casimir formulation. Variation of the rotation angle of the mirror as a function of the applied voltage is obtained and the instability parameters i.e., pull-in voltage and pull-in angle of the system are determined. The effect of Casimir forces on the size-dependent pull-in instability of the system is discussed. Furthermore, the minimum gap between the mirror and the ground to prevent stiction (due to Casimir force) is determined as a function of material length scale parameter. It is found that the proposed model is able to predict the experimental results more accurately than the previous classical model...

In this paper, the static response and pull-in instability of nanotweezers fabricated from carbon nanotubes (CNT) are theoretically investigated considering the effects of the Coulomb electrostatic and van der Waals molecular attractions. For this purpose, a nanoscale continuum model is employed to obtain the nonlinear constitutive equation of this nano-device. The van der Waals attraction is computed from the simplified Lennard-Jones potential. In order to solve the nonlinear constitutive equation of the nanotweezers, three different approaches, e.g. developing a lumped parameter model, applying the analytical modified Adomian decomposition (MAD) and using a commercial numerical integration routine, are employed. The obtained results are in good agreement with experimental measurements as reported in the literature. As a case study, we have investigated a freestanding nanotweezer and have determined the detachment length and minimum initial gap. Furthermore, range of dominancy of the molecular attraction has been discussed.

Carbon nanotube (CNT) tweezers are composed of two parallel cantilever CNTs with a distance in between. In this paper, the static response and instability of CNT-made nano-tweezers is theoretically investigated considering the effects of Coulomb electrostatic force and van der Waals molecular attraction. For this purpose, a nano-scale continuum model is employed to obtain the nonlinear constitutive equation of the nano-tweezers. The Euler–Bernoulli beam theory is applied to model the elastic response of the CNT. The van der Waals attraction is computed from the simplified Lennard-Jones potential. In order to solve the nonlinear constitutive equation of the system, three approaches, e.g. the hemotopy perturbation method (HPM), the Adomian decomposition (AD) and the finite difference method (FDM) are employed. The obtained results are in good agreement with the experimental measurements. As a case study, freestanding CNT tweezers has been investigated and the detachment length and minimum initial gap of the tweezers are determined. Moreover, the effective operation range of the van der Waals attraction that affects the instability behavior of the CNT tweezers is discussed.

ZnO nanoparticles are synthesized and applied as ethanol gas sensors. In some cases, the sensitivity and response time of these particles are shown to be higher than that has been reported in the literature. It has been investigated that the most possible reason for this higher gas sensing performance can be attributed to the quantity of the activity coefficient of its initial components. However, other effects such as pH and thermal decomposition are of importance as well. Specific ion interaction (SIT) model is applied to derive the mean activity coefficient values of the additives used in synthesis of ZnO nanoparticles.

It has been well established that the physical performance of nanodevices might be affected by the microstructure. Herein, a two-degree-of-freedom model base on the modified couple stress theory is developed to incorporate the impact of microstructure in the torsion/bending coupled instability of rotational nanoscanner. Effect of microstructure dependency on the instability parameters is determined as a function of the microstructure parameter, bending/torsion coupling ratio, van der Waals force parameter and geometrical dimensions. It is found that the bending/torsion coupling substantially affects the stable behavior of the scanners especially those with long rotational beam elements. Impact of microstructure on instability voltage of the nanoscanner depends on coupling ratio and the conquering bending mode over torsion mode. This effect is more highlighted for higher values of coupling ratio. Depending on the geometry and material characteristics, the presented model is able to simulate both hardening behavior (due to microstructure) and softening behavior (due to torsion/bending coupling) of the nanoscanners.

Herein, the torsion–bending coupled pull-in instability of rotational electromechanical nano–micro mirror is investigated using a two-degree-of-freedom (2-DOF) model. Two nano-scale phenomena (i.e., surface effect and molecular van der Waals attraction) are incorporated in the model. None of the previous 2-DOF models have taken these nano-scale effects into account. Results reveal that the influences of surface effects and intermolecular force on the coupled pull-in voltage of the nano–micro mirror highly depend on the geometrical characteristics of the system. It is found that if the mirror dimensions are of the order of the material length scale parameters, the pull-in characteristics computed via the present 2-DOF model will highly differ from those predicted by previous one-degree-of-freedom (1-DOF) models. Interestingly, the influence of surface effects on pull-in voltage of the system highly depends on the bending/torsion coupling ratio. Moreover, results show that the van der Waals force can reduce the pull-in voltage of the mirror. This deteriorating effect is more highlighted in the torsional mode than the bending mode.

The fracture behavior of a hybrid-rubber-modified epoxy system was investigated. The modified epoxy included amine-terminated butadiene acrylonitrile (ATBN) rubber and recycled tire particles as fine and coarse modifiers, respectively. The results of the fracture toughness (KIC) measurement of the blends revealed synergistic toughening in the hybrid system when 7.5-phr small particles (ATBN) and 2.5-phr large particles (recycled tire) were incorporated. Transmission optical micrographs showed different toughening mechanisms for the blends; fine ATBN particles increased the toughness by increasing the size of the damage zone and respective plastic deformation in the vicinity of the crack tip. However, in the case of hybrid resin, coarse recycled rubber particles acted as large stress concentrators and resulted in the branching of the original crack tip. Mode mixity at the branch tips led to synergistic KIC in the hybrid system. It seemed that the ductility of the matrix played an effective role in the nature of the crack-tip damage zone in the hybrid epoxies. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1–1000 mm/min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1–10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10–1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012