Vibration and instability of fluid-conveyed smart micro-tubes based on magneto-electro-elasticity beam model

The main scope of this paper is to propose a theoretical approach to investigate the stability of smart micro-tubes conveying fluid based on magneto-thermo-electro-elasticity theory. These micro-tubes are made of isotropic magneto-electro-elastic (MEE) material in which an incompressible fluid is flowing through it axially. Based on the Euler–Bernoulli beam model, using Hamilton’s variational principle and employing constitutive relations for MEE materials and Maxwell’s equations, the dimensionless governing equations pertinent to the free vibration of MEE tubes are derived. The effects of magnetization, thermal field, electricity and elasticity are modeled where the newly invented equation indicates the innovative properties of smart fluid-conveying MEE micro-tubes. Applying Galerkin method, eigenvalue analysis is performed and the critical fluid velocity and consequently stability of the system for both simply supported and clamped–clamped cases are studied. The effects of magnetic/electric potential and temperature changes on the stability of the system are discussed in detail. The obtained numerical results reveal that applying magneto-electric potential and temperature change has considerable effect on the stability of the system, which can be useful to control the critical fluid velocity in designing of smart fluid-conveying micro-tubes. Furthermore, the critical fluid velocities for different operating fluids with various densities are studied. It is shown that by increasing the fluid density the critical fluid velocity is decreased.     

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO₂–Al₂O₃–ZrO₂ were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.     

Modeling,analysis and multi-objective optimization of twist extrusion process using predictive models and meta-heuristic approaches,based on finite element results

Recently, twist extrusion has found extensive applications as a novel method of severe plastic deformation for grain refining of materials. In this paper, two prominent predictive models, response surface method and artificial neural network (ANN) are employed together with results of finite element simulation to model twist extrusion process. Twist angle, friction factor and ram speed are selected as input variables and imposed effective plastic strain, strain homogeneity and maximum punch force are considered as output parameters. Comparison between results shows that ANN outperforms response surface method in modeling twist extrusion process. In addition, statistical analysis of response surface shows that twist extrusion and friction factor have the most and ram speed has the least effect on output parameters at room temperature. Also, optimization of twist extrusion process was carried out by a combination of neural network model and multi-objective meta-heuristic optimization algorithms. For this reason, three prominent multi-objective algorithms, non-dominated sorting genetic algorithm, strength pareto evolutionary algorithm and multi-objective particle swarm optimization (MOPSO) were utilized. Results showed that MOPSO algorithm has relative superiority over other algorithms to find the optimal points.     

Mechanical behavior of a circular micro plate subjected to uniform hydrostatic and non-uniform electrostatic pressure

Circular micro plates are used in the many Microelectromechanical devices as micropumps and micro pressure sensors. All such systems exhibit a static instability phenomenon (Divergence) which is known as the “pull-in” instability. In this paper a distributed model was used to investigate the pull-in instability of a circular micro plate subjected to non-uniform electrostatic pressure and uniform hydrostatic pressure. The non-linear governing equation was derived and in order to linearize the obtained governing equations, step by step linearization method was used, then the linear system of equation was solved by finite difference method. The obtained results for only electrostatic actuation were compared with the existing results and good agreement has been achieved. There are exist two method of actuation. The pull-in voltages for these two actuation mechanism were investigated and the obtained results exhibited different effects on each actuation mechanism.     

Investigation of nonlinear dynamic behavior of a capacitive carbon nano-tube based electromechanical switch considering van der Waals force

Microsystem Technologies - In this study, nonlinear dynamic behavior of a capacitive carbon nano-tube switch is investigated considering van der Waals (vdW) force. The carbon nano-tube is...     

Designing and analyzing of a piezoelectric energy harvester with tunable system natural frequency for WSN and biosensing applications

A new structure for PEH with actuation piezoelectric layer for shifting natural frequency of the system is proposed. Beams are consisted to be Si and AlN piezoelectric which is deposited on fixed–fixed beams that produces high stress points and generates more power in comparison to the other cantilever beam PEHs. This PEH with ability of shifting system natural frequency is designed to the size of 0.25 cm² using optimum available space. Actuation piezoelectric layers added on both sides of the beams provides possibility of continues reducing systems natural frequency to less than 10 Hz. Accomplished simulation also confirms theoretical calculation done by PDE method to estimate natural frequency of the system. The natural frequency of the system without actuation voltage is 58 Hz that with 1 g acceleration generated 4.27 V and 71 µW electrical power which can be used in WSN and biosensing applications.

     

Stability analysis of an electrostatically actuated out of plane MEMS structure

In the present research, stability and static analyses of microelectromechanical systems microstructure were investigated by presenting an out-of-plane structure for a lumped mass. The presented model consists of two stationary electrodes in the same plane along with a flexible electrode above and in the middle of the two electrodes. The nonlinear electrostatic force was valuated via numerical methods implemented in COMSOL software where three-dimensional simulations were performed for different gaps. The obtained numerical results were compared to those of previous research works, indicating a good agreement. Continuing with the research, curves of electrostatic and spring forces were demonstrated for different scenarios, with the intersection points (i.e., equilibrium points) further plotted. Also drawn were plots of deflection versus voltage for different cases and phase and time history curves for different values of applied voltage followed by introducing and explaining pull-in and pull-out snap-through voltages in the system for a specific design. It is worth noting that, at voltages between the pull-in and pull-out snap-through voltages, the system was in bi-stable state. Based on the obtained results, it was observed that the gap between the two electrodes and the applied voltage play significant roles in the number and type of the equilibrium points of the system.

     

Hybrid silane-treated glass fabric/epoxy composites: tensile properties by micromechanical approach

The effect of interface modification on the interfacial adhesion and tensile properties of glass fabric/epoxy composites was evaluated in two directions of 0° and +45°. Herein, the glass fabric surface was modified by colloidal nanosilica particles and by a new blend of silane-coupling agents including both reactive and non-reactive silanes. Composite samples with high strength and toughness were obtained. A simultaneous improvement of tensile strength and toughness was observed for an epoxy composite reinforced with a hybrid-sized glass fabric including silane mixture and nanosilica. In fact, the incorporation of colloidal silica into the hybrid sizing dramatically modified the fiber surface texture and created mechanical interlocking between the glass fabric and resin. The results were analyzed by the rule of mixtures (ROM), Halpin–Tsai (H–T), and Chamis equations. It was found that the ROM equations provided approximate upper bound values for all investigated composite samples. In the samples containing nanosilica, the shear and elastic moduli values calculated by the Chamis and ROM equations showed good agreement with those obtained from experiments. However, in other samples, the values calculated by the H–T equation showed a better agreement with the experimental data. The analysis of fracture surfaces indicated that both silane and nanosilica particles had influence on the mode of failures at the interface.