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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. Source

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. Source

Aloui S.,Ecole Centrale Nantes | Aloui S.,Applied Mechanics and Systems Research Laboratory | Othman R.,Ecole 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. Source

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. Source

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. Source

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