Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Study on the Pull-In Instability of Gold Micro-Switches Using Variable Length Scale Parameter
114
123
EN
M
Fathalilou
Department of Mechanical Engineering, Khoy Branch, Islamic Azad University
m.fathalilou@tabrizu.ac.ir
M
Sadeghi
Department of Mechanical Engineering, University of Tabriz
G
Rezazadeh
Department of Mechanical Engineering, Khoy Branch, Islamic Azad University
M
Jalilpour
Department of Mechanical Engineering, Khoy Branch, Islamic Azad University
A
Naghilou
Department of Mechanical Engineering, Khoy Branch, Islamic Azad University
S
Ahouighazvin
Department of Mechanical Engineering, Khoy Branch, Islamic Azad University
In this paper, the size dependent behavior of the gold micro-switches has been studied. This behavior becomes noticeable for a structure when the characteristic size such as thickness or diameter is close to its internal length-scale parameter. The size dependent effect is insignificant for the high ratio of the characteristic size to the length-scale parameter, which is the case of the silicon base micro-beams. On the other hand, in some types of micro-beams like gold base, the size dependent effect cannot be overlooked. In such cases, ignoring this behavior in modeling will lead to incorrect results. Some previous researchers have applied classic beam theory on their models and imposed a considerable hypothetical value of residual stress to match their theoretical results with the experimental ones. In this study, by obtaining the equilibrium positions or fixed points of the gold micro-beam, a considerable difference between the obtained fixed points using classic beam theory and modified couple stress theory has been shown. In addition, it has been shown that the calculated pull-in voltages using modified couple stress theory are much closer to the experimental results than those obtained by classic beam theory. Finally, it has been shown that considering a unique value of length scale parameter, especially for the smallest values of the beam thicknesses, may leads to inaccurate results and variable length scale parameter should be considered.
MEMS,Gold micro-switch,Couple stress theory,Length-scale parameter,Pull-in voltage
http://jsm.iau-arak.ac.ir/article_514403.html
http://jsm.iau-arak.ac.ir/article_514403_a7a140f0084cf14697865209ac9db05c.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Performance Analysis of Different Modified MR Engines Mounts
124
131
EN
T
Feyzi
Department of Mechanical Engineering, Isfahan University of Technology
R
Tikani
Department of Mechanical Engineering, Isfahan University of Technology
M
Esfahanian
Department of Mechanical Engineering, Isfahan University of Technology
mesf1964@cc.iut.ac.ir
S
Ziaei Rad
Department of Mechanical Engineering, Isfahan University of Technology
Increasing current vehicle development trends for small, light, front wheel drive vehicles with low idle speeds have been forced automotive industries to use hydraulic engine mounts for further improvement in vibration, noise and harshness (NVH) performance of the vehicles. However, with the development of modern vehicle designs such as hybrid vehicles and variable engine management systems which have different operational modes, more sophisticated engine mounting systems are required to effectively response to each operational mode. Magnetorheological (MR) engine mount is a semi-active hydraulic engine mount, containing MR fluid, which can alter its dynamic behavior as a result of applying magnetic field. In this paper, design concept of two MR mounts is presented and their dynamic behavior is simulated. It is shown that the simulation methods used in this paper for simulating the dynamic behaviors of the MR mounts are effective with which the dynamic characteristic analysis and design optimization of MR mounts can be performed before its prototype development. Because of increasing demands for semi-active MR mounts in automotive industries, this can ensure their low cost and high quality for development.
Hydraulic engine,Mr fluid,Dynamic stiffness,Vibration isolation
http://jsm.iau-arak.ac.ir/article_514404.html
http://jsm.iau-arak.ac.ir/article_514404_cea69c6463650a8f3d89d628b5d75e82.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Thermal Stress Analysis of a Composite Cylinder Reinforced with FG SWCNTs
132
141
EN
A
Ghorbanpour Arani
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan---
Institute of Nanoscience & Nanotechnology, University of Kashan
aghorban@kashanu.ac.ir
S
Amir
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
V
Sadooghi
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
M
Mohammadimehr
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
Thermal stress analysis of a thick-walled cylinder reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) is considered in radial direction. Thick-walled cylinder is subjected to a thermal field. Two layouts of variations in the volume fraction of SWCNTs were considered in the composite cylinder along the radius from inner to outer surface, where their names are incrementally decreasing (Inc Dec) and incrementally increasing (Inc Inc). Micromechanical models based on the Mori-Tanaka is used to define effective macroscopic properties of the nano composite shell. Using equations of motion, stress-strain and their corresponding constitutive correlations of a polystyrene vessel, a second order ordinary differential equation was proposed based on the radial displacement. The higher order governing equation was solved in order to obtain the distribution of displacement and thermal stresses in radial, circumferential and axial directions. The results indicate that FG distributions of SWCNTs have significant effect on thermal stresses and displacements in axial, radial and circumferential directions, so that in Inc Inc layout, the radial and circumferential stresses are lower than of other FG structures.
Thermal Stress analysis,Nano Composite,Mori-Tanaka,FG SWCNTs reinforcement,Thick-walled cylinder
http://jsm.iau-arak.ac.ir/article_514405.html
http://jsm.iau-arak.ac.ir/article_514405_49f8a2966a7245c6cc36f5c80251f379.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Time-Dependent Thermo-Electro-Mechanical Creep Behavior of Radially Polarized FGPM Rotating Cylinder
142
157
EN
A
Ghorbanpour Arani
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan---
Thermoelasticity Center of Excellence, Department of Mechanical Engineering, Amirkabir University of Technology
aghorban@kashanu.ac.ir
R
Kolahchi
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
A.A
Mosallaie Barzoki
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
A
Loghman
0000-0002-8292-8958
Department of Mechanical Engineering, Faculty of Engineering, University of Kashan
aloghman@kashanu.ac.ir
Time-dependent creep analysis is crucial for the performance and reliability of piezoactuators used for high-precision positioning and load-bearing applications. In this study history of stresses, deformations and electric potential of hollow rotating cylinders made of functionally graded piezoelectric material (FGPM), e.g., PZT_7A have been investigated using Mendelson’s method of successive elastic solution. Loading is composed of an internal pressure, a distributed temperature field, an inertia body force and a constant electric potential difference between the inner and outer surfaces of the FGPM cylinder. All the mechanical, thermal and piezoelectric properties are assumed to be the same power functions of the radial graded direction. Using equations of equilibrium, strain displacement, stress-strain relation and the electric potential equation a differential equation containing creep strains for displacement is derived. A semi-analytical method in conjunction with the method of successive approximation has therefore been proposed for this analysis. It has been found that a major redistribution for electric potential take place throughout the thickness. Electric potentials are increasing with time in the same direction as the compressive radial stress histories. That is the electric potential histories are induced by the compressive radial stress histories during creep deformation of the FGPM cylinder.
Time-dependent,Thermo-electro-mechanical creep,Stress histories,Electric potential histories,FGPM Rotating cylinder
http://jsm.iau-arak.ac.ir/article_514406.html
http://jsm.iau-arak.ac.ir/article_514406_0b81a18860ea8c27c2c5143050f96ecf.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Mechanical Behavior of a FGM Capacitive Micro-Beam Subjected to a Heat Source
158
171
EN
I
JafarSadeghi-Pournaki
Mechanical Engineering Department, Urmia University
M.R
Zamanzadeh
Mechanical Engineering Department, Urmia University
R
Shabani
Mechanical Engineering Department, Urmia University
G
Rezazadeh
Mechanical Engineering Department, Urmia University
g.rezazadeh@urmia.ac.ir
This paper presents mechanical behavior of a functionally graded (FG) cantilever micro-beam subjected to a nonlinear electrostatic pressure and thermal moment considering effects of material length scale parameters. Material properties through the beam thickness direction are graded. The top surface of the micro-beam is made of pure metal and the bottom surface from a mixture of metal and ceramic. The material properties through the thickness direction follow the volume fraction of the constitutive materials in exponential function form. The governing nonlinear thermo-electro-mechanical differential equation based on <em>Euler-Bernoulli</em> beam theory assumptions is derived using modified couple stress theory (MCST) and is solved using the Galerkin based weighted residual method. The effects of the electrostatic pressure and temperature changes on the deflection and stability of the FGM micro-beam, having various ceramic constituent percents, are studied. The obtained results are compared with the results predicted by classic theory (CT) and for some cases are verified with those reported in the literature.
FGM Cantilever micro-beam,Euler–Bernoulli,Pull-in voltage,Size-dependent,Exponential volume fraction law
http://jsm.iau-arak.ac.ir/article_514408.html
http://jsm.iau-arak.ac.ir/article_514408_f493673cf4e83a981ab358918652b4c9.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Free Vibration of Thick Isotropic Plates Using Trigonometric Shear Deformation Theory
172
182
EN
Y.M
Ghugal
Department of Applied Mechanics, Government Engineering College, Aurangabad-431005 (Maharashtra State)
ghugal@rediffmail.com
A.S
Sayyad
Department of Applied Mechanics, Government Engineering College, Aurangabad-431005 (Maharashtra State)
In this paper a variationally consistent trigonometric shear deformation theory is presented for the free vibration of thick isotropic square and rectangular plate. In this displacement based theory, the in-plane displacement field uses sinusoidal function in terms of thickness coordinate to include the shear deformation effect. The cosine function in terms of thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. Results of frequency of bending mode, thickness-shear mode and thickness-stretch mode are obtained from free vibration of simply supported isotropic square and rectangular plates and compared with those of other refined theories and frequencies from exact theory. Present theory yields exact dynamic shear correction factor π<sup>2</sup>/12 from thickness shear motion of the plate.
Shear deformation,Thick isotropic plate,Shear correction factor,Transverse normal strain,Free vibration,Thickness shear frequencies
http://jsm.iau-arak.ac.ir/article_514411.html
http://jsm.iau-arak.ac.ir/article_514411_9cd976687f1a4475ff1c9da88145a2bf.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
A Power Series Solution for Free Vibration of Variable Thickness Mindlin Circular Plates with Two-Directional Material Heterogeneity and Elastic Foundations
183
197
EN
M.M
Alipour
Faculty of Mechanical Engineering, K.N. Toosi University of Technology
M
Shariyat
Faculty of Mechanical Engineering, K.N. Toosi University of Technology
m_shariyat@yahoo.com
In the present paper, a semi-analytical solution is presented for free vibration analysis of circular plates with complex combinations of the geometric parameters, edge-conditions, material heterogeneity, and elastic foundation coefficients. The presented solution covers many engineering applications. The plate is assumed to have a variable thickness and made of a heterogeneous material whose properties vary in both radial and transverse directions. While the edge is simply-supported, clamped, or free; the bottom surface of the plate is resting on a two-parameter (<em>Winkler-Pasternak</em>) elastic foundation. A comprehensive sensitivity analysis including evaluating effects of various parameters is carries out. <em>Mindlin</em> theory is employed for derivation of the governing equations whereas the differential transform method is used to solve the resulted equations. In this regard, both the in-plane and rotary inertia are considered. Results show that degradations caused by a group of the factors (e.g., the geometric parameters) in the global behavior of the structure may be compensated by another group of factors of different nature (e.g, the material heterogeneity parameters). Moreover, employing the elastic foundation leads to higher natural frequencies and postponing the resonances.
Free vibration,Circular plate,Elastic foundation,Two-directional functionally graded material,Variable thickness,Differential transform
http://jsm.iau-arak.ac.ir/article_514412.html
http://jsm.iau-arak.ac.ir/article_514412_b7db117d03260b4f8ff0e0ec7f99c634.pdf
Islamic Azad University Arak Branch
Journal of Solid Mechanics
2008-3505
2008-7683
3
2
2011
06
30
Effect of Boundary Condition on Pre-Existing Crack Under Fatigue Loading
198
207
EN
V.K
Singh
Department of Mechanical Engineering, College of Technology, Govind Ballabh Pant University of Agriculture & Technology
vks2319@yahoo.co.in
P.C
Gope
Department of Mechanical Engineering, College of Technology, Govind Ballabh Pant University of Agriculture & Technology
pcgope@rediffmail.com
R.K
Bhagat
Department of Mechanical Engineering, College of Technology, Govind Ballabh Pant University of Agriculture & Technology
In this paper, the present investigation has been conducted keeping in mind some of the problems concerning the crack propagation direction and growth under constant loading in an inclined crack geometry. The present studies mainly focused on the development and modifications in the crack growth criterion to account the biaxial, shear loading and number of stress terms. Existing criteria for the prediction of crack initiation direction have been modified taking higher order stress terms. The effective methods of experimentally determining the stress intensity factor for a body containing a crack is to analyze the isochromatic pattern obtained from a photoelastic model. The effect of biaxial load factor, crack angle, Crack length/width of specimen and length of specimen/width of specimen were studied and a regression model was developed for geometry correction to predict stress intensity factor for tearing mode and intensity factor for shearing mode. This approach is being used to predict crack growth trajectory under biaxial cyclic loading by assuming that the crack may grow in a number of discrete steps using the vectorial method. MTS criterion (Maximum Tangential Stress criterion) is used for prediction of crack initiating angle. The crack growth trajectory has been determined by cycle simulation procedure.
Stress intensity factor,crack growth,Photo elasticity
http://jsm.iau-arak.ac.ir/article_514414.html
http://jsm.iau-arak.ac.ir/article_514414_495bd84653cc62893a5534647dd77771.pdf