جستجوی مقالات مرتبط با کلیدواژه "nano beam" در نشریات گروه "مکانیک"

In this work, a comprehensive wave propagation analysis is performed on rotating viscoelastic nanobeams resting on viscoelastic Winkler-Pasternak foundations. Here, a novel non-classical mechanical model is developed to describe accurate wave propagation behavior for viscoelastic nanobeams. In fact, to capture both hardening and softening behaviors of materials during wave propagation, general nonlocal theory (GNT) is applied to establish the governing motion of equations. Unlike Eringen’s nonlocal theory, general nonlocal theory employs two different nonlocal parameters refers to normal and shear strains. Also, Kelvin-Voigt model along with Timoshenko beam theory are considered to extract the equations and analytical solution is employed to make the results. The results are obtained for longitudinal (LA), torsional (TO) and transverse (TA) types of wave propagations. Moreover, the effects of nonlocal parameters, Kelvin-Voigt damping, foundation damping, Winkler-Pasternak coefficients and rotating velocity are illustrated and discussed in details especially for TO and TA types of wave propagation. The results show the effect of each of the mentioned parameters on the frequency for all types of wave propagation.

Many researches have been carried out for modeling of micro/nano electromechanical systems instabilities, in which both movable and substrate electrodes are at the same size; however, there is no research considering the static and dynamic pull-in instabilities of micro/nano actuators with a smaller substrate electrode in the presence of small size effects. In the present study, the static and dynamic behaviors of partially affected clamped micro/nano actuators are investigated and the effects of position and length of the substrate electrode are analyzed. The non-linear Euler-Bernoulli governing equation of the beam motion and the corresponding boundary conditions are derived using the Modified couple stress theory. Finite element method is utilized to solve the governing equations. In order to investigate the accuracy of the utilized finite element method, the obtained results are compared with those available in the literature and a good agreement between them was found. The results demonstrate that a decrease of the substrate electrode length leads to an increase of the required pull-in voltage and the pull-in capillary force. Moreover, a small reduction in the pull-in deflection of the nano-beam is observed because of the decrease of the substrate electrode. Finally, a new parameter, named as balanced size effect-capillary force which changes the trend of the behavior of the nano-beam, is introduced.

In the nanoscale, the continuity assumption may be violated, and hence, the classical theories, which have been introduced based on the continuity assumption, may lose their accuracy. Therefore, new size-dependent continuum theories are demanded for proper design and analysis of micro/nano-electro-mechanical systems. The aim of the present study is to develop a new non-linear theoretical model, based on the Modified couple stress theory, for analysis of static and dynamic pull-in instabilities of nanobeams, utilized in nano switches. In the present model, the size effect parameter, the fringing field effect, the electro static forces, the intermolecular forces (Casimir and Van der Walls) are taken into account. The non-linear Euler-Bernoulli governing equation of the beam motion and the corresponding boundary conditions are derived by using Hamilton’s principle. The results show that the decrease in the size of the beam increases the beam stiffness. An increase in the fringing field effect, the size effect parameter or decrease in intermolecular forces as well as decrease in the substrate length would increase the ultimate pull-in voltage. Also, when a cantilever nanobeam is affected partially from the free-side end, the effect on the increase of the pull-in parameters of the intermolecular forces and the voltage is greater than that of the nanobeam is affected partially from its support side.

In this paper deflection and free vibration of sandwich panel is studied. The core of Sandwich panels is made of hexagonal honeycomb and faces are made of two different materials of Carbon Fiber Reinforced Plastic and K-aryl/epoxy covering. The governing equations are deduced from the First order Sheer Deformation Theory (FSDT) and they are solved using Generalized Differential Quadrature Method (GDQM). The classical method in the references is used to verify the DQ method and to show that the applied GDQM method has a good results with compared to the references. Deflection of sandwich panel is investigated with two different load types. Finally natural frequency for the first 4 modes and the two different faces materials are calculated and the effect of various lengths to core thickness ratios and faces to honeycomb core thickness ratios are studied. Further, the effect of foundation stiffness coefficient on deflection and natural frequency are showed.

In this article, a novel method, namely full modified nonlocal (FMNL) theory, for analysis of nano structures under different case loading. Also bending analysis of rectangular nano plates and nano beams are investigated in order to demonstrate the effectiveness of the presented theory. For this purpose, a complete representation of governing equation and boundary conditions are derived based on the infinite series of modified nonlocal constitutive equations by applying the variational principle. It is shown that by rearranging and then computing the sum of the infinite series which appears in the maximum bending deflection, the truncation errors will be eliminated. In addition, the results of the presented method are compared with MD simulations to confirm the validity of FMNL theory. One of the advantages of the FMNL theory is that the defect of nonlocal (NL) theory in vanishing of small scale effect for some problems can be resolved. Furthermore, the FMNL theory will be a criterion for accuracy of the primary modified nonlocal (PMNL) theory that considers only two terms of the series of the modified nonlocal constitutive equation in predicting maximum bending deflections.

In this paper deflection and free vibration of sandwich panel is studied. The core of Sandwich panels is made of hexagonal honeycomb and faces are made of two different materials of Carbon Fiber Reinforced Plastic and K-aryl/epoxy covering. The governing equations are deduced from the First order Sheer Deformation Theory (FSDT) and they are solved using Generalized Differential Quadrature Method (GDQM). The classical method in the references is used to verify the DQ method and to show that the applied GDQM method has a good results with compared to the references. Deflection of sandwich panel is investigated with two different load types. Finally natural frequency for the first 4 modes and the two different faces materials are calculated and the effect of various lengths to core thickness ratios and faces to honeycomb core thickness ratios are studied. Further, the effect of foundation stiffness coefficient on deflection and natural frequency are showed.

In the present paper, electrical energy harvesting from random vibrations of an Euler-Bernoulli nano-beam with two piezoelectric layers is investigated. The beam is composed of an aluminum layer together with two piezoelectric ceramic layers (PZT 5A) serving as energy harvesting sensors. In the proposed method, the equations governing the bimorph nano-beam will be analytically derived using classical beam theory with corresponding modification coefficients to the nano-structure applied. Then, the derived system of equations will be solved following Kantorovich method. Assumed boundary conditions for the nano-beam are as follows: a clamped end with the mass concentrated at the free end of the beam. Further, the input activation function of the system for energy harvesting was taken as being random. Since the objective of this research is to investigate the amount of harvested energy, the section on the results provides associated voltage and maximum output power curves with the bimorph nano-beam under random activation and input white noise, while also presenting the effects of characteristics and scale factor of the nano-particles on the amount of harvested energy.