Applied Mechanics and Systems Research Laboratory

Al Marsá, Tunisia

Applied Mechanics and Systems Research Laboratory

Al Marsá, Tunisia
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Elloumi R.,Applied Mechanics and Systems Research Laboratory | Kallel-Kamoun I.,University of Sfax | El-Borgi S.,Applied Mechanics and Systems Research Laboratory
Mechanics of Materials | Year: 2010

In this paper, we consider the two-dimensional nonlinear partial slip contact problem between a non-homogeneous isotropic graded half-plane and a rigid punch of an arbitrary profile subjected to a normal load. The graded medium is modeled as a non-homogeneous isotropic material with an exponentially varying shear modulus and a constant Poisson's ratio. The problem is formulated under plane strain conditions. Using standard Fourier transform, the problem is reduced to a set of two coupled singular integral equations in which the main unknowns are the normal and the tangential contact stresses and the stick zone size. An asymptotic analysis is performed to extract the proper singularities from the kernels. Using Gauss-Chebychev integration formulas, the two coupled equations are solved by sequential iterations. The objective of this paper is to study the effect of the graded medium non-homogeneity parameter and the friction coefficient on the size of the stick zone and the contact stresses for the cases of flat and circular stamp profiles. Particular attention is also paid to the effect of the coupling between the normal and the tangential contact stresses. © 2010 Elsevier Ltd. All rights reserved.


Kallel-Kamoun I.,University of Sfax | Elloumi R.,Applied Mechanics and Systems Research Laboratory | El-Borgi S.,Applied Mechanics and Systems Research Laboratory
Journal of Computational and Theoretical Nanoscience | Year: 2010

We consider in this paper the two-dimensional nonlinear partial slip contact problem between a non-homogeneous isotropic graded half plane and a rigid punch of an arbitrary profile subjected to a monotonically increasing normal load. The graded medium is modeled as a non-homogeneous isotropic material with an exponentially varying shear modulus and a constant Poisson's ratio. Using standard Fourier Transform, the problem is formulated under plane strain conditions and is reduced to a set of singular integral equations. An asymptotic analysis is performed to extract the proper singularities from the kernels, resulting in two integral equations which are solved numerically using Gauss-Chebechev integration formulas. Based on the Goodman approximation, the contact problem is simplified and an iterative method is developed to determine the stick-slip zone, as well as the normal and tangential tractions in the entire contact zone. The objective of this paper is to study the effect of the graded medium non-homogeneity parameter and the friction coefficient on the size of the stick zone and the contact stresses for the cases of flat and circular stamp profiles. The proposed solution method can be potentially used to study piezoelectric indentation problems in nanocomposites involving flexoelectricity and polarization gradient effects. Copyright © 2010 American Scientific Publishers.


Nayfeh A.H.,Virginia Polytechnic Institute and State University | Ouakad H.M.,Binghamton University State University of New York | Najar F.,Applied Mechanics and Systems Research Laboratory | Choura S.,Applied Mechanics and Systems Research Laboratory | Abdel-Rahman E.M.,University of Waterloo
Nonlinear Dynamics | Year: 2010

We develop a mathematical model for a resonant gas sensor made up of an microplate electrostatically actuated and attached to the end of a cantilever microbeam. The model considers the microbeam as a continuous medium, the plate as a rigid body, and the electrostatic force as a nonlinear function of the displacement and the voltage applied underneath the microplate. We derive closed-form solutions to the static and eigenvalue problems associated with the microsystem. The Galerkin method is used to discretize the distributed-parameter model and, thus, approximate it by a set of nonlinear ordinary-differential equations that describe the microsystem dynamics. By comparing the exact solution to that associated with the reduced-order model, we show that using the first mode shape alone is sufficient to approximate the static behavior. We employ the Finite Difference Method (FDM) to discretize the orbits of motion and solve the resulting nonlinear algebraic equations for the limit cycles. The stability of these cycles is determined by combining the FDM discretization with Floquet theory. We investigate the basin of attraction of bounded motion for two cases: unforced and damped, and forced and damped systems. In order to detect the lower limit of the forcing at which homoclinic points appear, we conduct a Melnikov analysis. We show the presence of a homoclinic point for a loading case and hence entanglement of the stable and unstable manifolds and non-smoothness of the boundary of the basin of attraction of bounded motion. © 2009 Springer Science+Business Media B.V.


Ghommem M.,Virginia Polytechnic Institute and State University | Nayfeh A.H.,Virginia Polytechnic Institute and State University | Choura S.,Applied Mechanics and Systems Research Laboratory | Najar F.,Applied Mechanics and Systems Research Laboratory | Abdel-Rahman E.M.,University of Waterloo
Journal of Sound and Vibration | Year: 2010

We develop a mathematical model of a microgyroscope whose principal component is a rotating cantilever beam equipped with a proof mass at its end. The microgyroscope undergoes two flexural vibrations that are coupled via base rotation about the microbeam longitudinal axis. The primary vibratory motion is produced in one direction (drive direction) of the microbeam by a pair of DC and AC voltages actuating the proof mass. The microbeam angular rotation induces a secondary vibration in the orthogonal (sense) direction actuated by a second DC voltage. Closed-form solutions are developed for the linearized problem to study the relationship between the base rotation and gyroscopic coupling. The response of the microgyroscope to variations in the DC voltage across the drive and sense electrodes and frequency of excitation are examined and a calibration curve of the gyroscope is obtained analytically. © 2010 Elsevier Ltd. All rights reserved.


Samaali H.,Micro Electro Thermal Systems Research Unit | Najar F.,Applied Mechanics and Systems Research Laboratory | Choura S.,Micro Electro Thermal Systems Research Unit | Nayfeh A.H.,Virginia Polytechnic Institute and State University | Masmoudi M.,Micro Electro Thermal Systems Research Unit
Nonlinear Dynamics | Year: 2011

In this paper, we propose the design of an ohmic contact RF microswitch with low voltage actuation, where the upper and lower microplates are displaceable. We develop a mathematical model for the RF microswitch made up of two electrostatically actuated microplates; each microplate is attached to the end of a microcantilever. We assume that the microbeams are flexible and that the microplates are rigid. The electrostatic force applied between the two microplates is a nonlinear function of the displacements and applied voltage. We formulate and solve the static and eigenvalue problems associated with the proposed microsystem. We also examine the dynamic behavior of the microswitch by calculating the limit-cycle solutions. We discretize the equations of motion by considering the first few dominant modes in the microsystem dynamics. We show that only two modes are sufficient to accurately simulate the response of the microsystem under DC and harmonic AC voltages. We demonstrate that the resulting static pull-in voltage and switching time are reduced by 30 and 45%, respectively, as compared to those of a single microbeam-microplate RF-microswitch. Finally, we investigate the global stability of the microswitch using different excitation conditions. © 2010 Springer Science+Business Media B.V.


Aloui S.,École Centrale Nantes | Aloui S.,Applied Mechanics and Systems Research Laboratory | Othman R.,École Centrale Nantes | Othman R.,King Abdulaziz University | And 2 more authors.
Mechanics Research Communications | Year: 2013

Abstract Because of their low mechanical wave speed, high strain rate testing of rubber is highly difficult. Indeed, stress and strain homogeneity is hard to achieve. In this paper, a semi-analytic inverse solution is proposed. This solution is based on a uni-axial stress state assumption in the specimen. Moreover, a new-Hookean law is assumed for rubber. The new method is successfully applied to a high strain rate test on a synthetic rubber. © 2012 Elsevier Ltd.


Loulizi A.,Applied Mechanics and Systems Research Laboratory
Construction and Building Materials | Year: 2010

Compacted sand concrete is being researched for potential usage in road construction because of shortage in gravel resources in many countries. However, one of the problems for this material with such application is shrinkage cracking. This paper presents the results of the unrestrained shrinkage test performed on three different compacted sand concrete mixes. Two existing shrinkage prediction models, namely the ACI 209 and the CEB 90, were used to fit the measured shrinkage data. The CEB 90 model with an application of a correction factor was found to perform well with compacted sand concrete. Based on the results of the shrinkage tests, joint spacing between compacted sand concrete slabs was calculated. © 2010 Elsevier Ltd. All rights reserved.


Ghozlane M.,Applied Mechanics and Systems Research Laboratory
Lecture Notes in Mechanical Engineering | Year: 2015

A simplified approach for modeling an open crack in a rotor based on the change of the flexibility is proposed in this paper. The crack model is incorporated in a two-node Timoshenko beam with 4 DOF at each node, which in turn represents one element of the finite element model of the rotor bearing system. The objectives of this work are twofold. The primary objective is to study the effect of the presence of crack on movement equation of rotor bearing system. Theoretically, it was shown that the crack generates external inertial, damping and elastic excitation forces which depend on the second harmonic of the rotational speed. The second objective is to calculate the dynamic response of the rotor bearing system with NEWMARK numerical integration method (average acceleration method) of non-linear equation. Results show that transverse crack produces peaks in the second harmonic of rotating speed modulated with natural frequency and the third harmonic of the rotation speed. The presence of a crack in a symmetric rotor causes asymmetry in the stiffness and consequently causes critical frequencies in backward whirl. © Springer International Publishing Switzerland 2015.


Rekik M.,Applied Mechanics and Systems Research Laboratory | Neifar M.,Applied Mechanics and Systems Research Laboratory | El-Borgi S.,Applied Mechanics and Systems Research Laboratory
International Journal of Solids and Structures | Year: 2010

In an attempt to simulate non-uniform coating delamination, the elasto-static problem of a penny shaped axisymmetric crack embedded in a functionally graded coating bonded to a homogeneous substrate subjected to crack surface tractions is considered. The coating's material gradient is parallel to the axisymmetric direction and is orthogonal to the crack plane. The graded coating is modeled as a non-homogeneous medium with an isotropic constitutive law. Using Hankel transform, the governing equations are converted into coupled singular integral equations, which are solved numerically to yield the crack tip stress intensity factors. The Finite Element Method was additionally used to model the crack problem. The main objective of this paper is to study the influence of the material non-homogeneity and the crack position on the stress intensity factors for the purpose of gaining better understanding on the behavior of graded coatings. © 2010 Elsevier Ltd. All rights reserved.


Rekik M.,Applied Mechanics and Systems Research Laboratory | Neifar M.,Applied Mechanics and Systems Research Laboratory | El-Borgi S.,Applied Mechanics and Systems Research Laboratory
Journal of Thermal Stresses | Year: 2011

The elastic-static problem of a partially insulated axisymmetric crack embedded in a graded coating bonded to a homogeneous substrate subjected to thermal loading is considered. The coating's gradient is parallel to the axisymmetric direction and is orthogonal to the crack plane. The graded coating is modeled as a nonhomogeneous medium with an isotropic constitutive law. Using Hankel transform, the heat conduction and the plane elasticity equations are converted into singular integral equations, which are solved numerically to yield the temperature distribution and the crack tip stress intensity factors. The Finite Element Method was additionally used to model the crack problem. The main objective of this paper is to study the influence of the material nonhomogeneity, partial insulation of the crack faces and the crack position on the stress intensity factors for the purpose of gaining better understanding on the behavior of graded coatings. Copyright © 2011 Taylor & Francis Group, LLC.

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