Golpayegan University of Technology

Golpayegan, Iran
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Bina R.,Golpayegan University of Technology | Mojahedi M.,Golpayegan University of Technology
International Journal of Applied Mechanics | Year: 2017

In this paper, the static and vibration responses of a microresonator by considering distributed proof mass are investigated based on the modified couple stress theory (MCST). The microresonator has a proof mass placed on the end of micro-cantilever beam and the proof mass actuated by electrostatic actuation. Due to the large length of proof mass compared to beam length, the proof mass is considered as a lengthy mass in the modeling. Hence, the resultant force and moment acting on the proof mass can be calculated by integrating the density of the electrostatic force along the mass length. Considering the length effects of the proof mass, MCST and electrostatic actuation, the equation of dynamic motion is derived using the extended Hamilton principle. Using a model approximation, i.e., Galerkin decomposition method, the governing equations of static and oscillatory motions are reduced and the resultant equation is solved by analytical (multiple scale method) and numerical methods. The result shows that the developed model, that includes distributed proof mass and size dependency effects, improves the results of pull-in instability voltage, natural frequency and amplitude of vibration. © 2017 World Scientific Publishing Europe Ltd.

Rafiaei S.M.,Golpayegan University of Technology
Materials Science- Poland | Year: 2016

In this investigation, Eu3+ doped YBO3 phosphors were synthesized by conventional solid state method at 1100 °C under atmosphere condition. Meanwhile, different amounts of LiCl, BaCl2 and CaCl2 were used as the flux compounds to modify the morphology of the phosphor particles and also final luminescent properties. It was concluded that even small amounts of fluxes play a vital role in the growth of particles. Then the emission and excitation photoluminescence spectra were measured respectively at λexc = 240 nm and λem = 610 nm and it was found that using 2 wt.% of flux compounds has a significant influence on the emission intensity of YBO3 phosphors. © Wroclaw University of Technology.

Klavzar S.,University of Ljubljana | Klavzar S.,University of Maribor | Nadjafi-Arani M.J.,University of Kashan | Nadjafi-Arani M.J.,Golpayegan University of Technology
European Journal of Combinatorics | Year: 2014

It is proved that the Wiener index of a weighted graph (G,w) can be expressed as the sum of the Wiener indices of weighted quotient graphs with respect to an arbitrary combination of Θ *-classes. Here Θ * denotes the transitive closure of Djoković-Winkler's relation Θ. A related result for edge-weighted graphs is also given and a class of graphs studied in Yousefi-Azari etal. (2011) [25] is characterized as partial cubes. © 2013 Elsevier Ltd.

Rahaeifard M.,Golpayegan University of Technology | Mojahedi M.,Golpayegan University of Technology
International Journal of Engineering Science | Year: 2017

This paper investigates the mechanical behavior of micro scaled laminated composite plates based on the modified couple stress theory. To this aim, considering a displacement field for the plate, the kinematic parameters such as strains and curvatures are calculated. Utilizing these kinematic parameters, classical stresses and couple stresses are obtained in each layer and consequently the equation of motion is derived using equilibrium equations of forces and moment of forces. Equivalent mechanical properties including the length scale parameter are presented for the composite plate. Using these equivalent quantities, static deflection and natural frequency of bilayer microplates are investigated and effects of size dependency on the mechanical behavior of the structure are assessed. © 2017 Elsevier Ltd

Rahaeifard M.,Golpayegan University of Technology | Ahmadian M.T.,Sharif University of Technology
International Journal of Engineering Science | Year: 2015

In this paper the static deflection and pull-in instability of electrostatically actuated microcantilevers is investigated based on the strain gradient theory. The equation of motion and boundary conditions are derived using Hamilton's principle and solved numerically. It is shown that the strain gradient theory predicts size dependent normalized static deflection and pull-in voltage for the microbeam while according to the classical theory the normalized behavior of the microbeam is independent of its size. The results of strain gradient theory are compared with those of classical and modified couple stress theories and also experimental observations. According to this comparison, the classical theory underestimates the stiffness of the microbeam and there is a gap between the results predicted by the classical theory and those observed in experiment. It is demonstrated that this gap can be reduced when utilizing the strain gradient theory. © 2014 Elsevier Ltd.

Baghani M.,Sharif University of Technology | Naghdabadi R.,Sharif University of Technology | Arghavani J.,Sharif University of Technology | Arghavani J.,Golpayegan University of Technology | And 2 more authors.
International Journal of Plasticity | Year: 2012

The ever increasing applications of shape memory polymers have motivated the development of appropriate constitutive models for these materials. In this work, we present a 3 D constitutive model for shape memory polymers under time-dependent multiaxial thermomechanical loadings in the small strain regime. The derivation is based on an additive decomposition of the strain into six parts and satisfying the second law of thermodynamics in Clausius-Duhem inequality form. In the constitutive model, the evolution laws for internal variables are derived during both cooling and heating thermomechanical loadings. The viscous effects are also fully accounted for in the proposed model. Further, we present the time-discrete form of the evolution equations in the implicit form. The model is validated by comparing the predicted results with different experimental data reported in the literature. Finally, using the finite element method, we solve two boundary value problems e.g., a 3 D beam and a medical stent made of shape memory polymers. © 2012 Elsevier Ltd. All rights reserved.

Rahaeifard M.,Golpayegan University of Technology
Composites Part B: Engineering | Year: 2015

In this paper, size-dependent static and dynamic behavior of functionally graded microbars is investigated on the basis of the modified couple stress theory. The equation of motion and corresponding boundary conditions are derived using Hamilton's principle and presented in the dimensionless form. Equivalent mechanical properties (i.e. shear modulus, density and length scale) are extracted for the functionally graded microbar based on the mechanical properties of the material constituents. In this work, it is shown that without any simplifying assumption, two equivalent length scale parameters can be defined for functionally graded bars and the size-dependent mechanical behavior of these components can be explained using these parameters. As an example, static and dynamic behavior of a functionally graded microbar with fixed-free boundary conditions is analyzed and the effect of size-dependency on mechanical behavior of this structure is discussed. © 2015 Elsevier Ltd. All rights reserved.

Tadi Beni Y.,Shahrekord University | Mehralian F.,Shahrekord University | Razavi H.,Golpayegan University of Technology
Composite Structures | Year: 2015

In this paper, size-dependent equations of motion for functionally graded cylindrical shell were developed using shear deformation model and rotation inertia. Material properties of the shell were assumed as continuously variable along thickness, and consistent with the variation in the component's volume fraction based on power law distribution. To consider the size effect, modified couple stress theory in conjunction with first order shear deformation shell model were used, and general equations of motion and classical and non-classical boundary conditions were derived based on Hamilton's principle. Finally, in the special case, using the Navier procedure, the free vibrations of simply supported functionally graded cylindrical nanoshell were obtained, and the effects of parameters such as dimensionless length scale parameter, distribution of FG properties, thickness, and length on the natural frequency were identified and was compared with the classical theory. Results obtained through the modified couple stress theory are indicative of the considerable effect of the size parameter, particularly in bigger thicknesses and shorter lengths of nanotubes, on the natural frequency. © 2014 Elsevier Ltd.

Rahaeifard M.,Golpayegan University of Technology
International Journal of Engineering Science | Year: 2016

This paper investigates the size-dependent static behavior of micro scale thermal actuators. The actuator is considered as a bilayer microcantilever and the modified couple stress theory is utilized to capture the size-dependency of the mechanical behavior of the device. Considering Euler–Bernoulli beam theory, the equations governing axial and lateral deformations of the microbeam are derived. Equivalent material properties including length scale parameter are defined for the bilayer microbeam and deflection of the actuator due to temperature change is calculated using these equivalent quantities. For numerical analysis, a bilayer microbeam made of aluminum and polysilicon is considered. For this microbeam, the lateral deflection due to temperature change is obtained based on the modified couple stress theory and compared to the results of the classical model and the influence of size-dependency on mechanical response of the microbeam is discussed. Finally, the effect of the thickness of layers on the lateral deflection of the device is investigated. © 2016 Elsevier Ltd

Rafiaei S.M.,Golpayegan University of Technology
Transactions of the Indian Institute of Metals | Year: 2016

In this paper, YVO4:Eu3+ nanophosphors were synthesized via the simple combustion method by urea and aniline, individually. The particle size of produced powders and the combustion flame temperature were explained in thermodynamic terms. These phosphors were characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscope and photoluminescence (PL) analyses. It was concluded that the amounts of released gas, adiabatic flame temperature, remaining compounds after combustion reaction, size of powders and optical properties depended strongly on the used combustion fuel. Also, the PL intensity of the phosphors synthesized by aniline was remarkably higher than that of phosphors synthesized by urea. © 2016 The Indian Institute of Metals - IIM

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