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1

Dynamical Behaviour of a Multi-Stage Epicyclic Gear Train

100%

Siala W. , Chaari F. , Fakhfakh T. , Haddar M.

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tom Vol. 31, No. 1

82-100

EN

For many years ago, much works were interested in the study of the dynamic behaviour of a simple epicyclical gear stages. But, in our knowledge there are very few or practically unexisting works dealing with the dynamic behaviour of multi stages epicyclical gear systems. This work is directed towards the study of the dynamic behaviour of an epicyclical double stages gear system without defects, by taking account of its essential components (gears, bearing...). Compared to the trains with parallel axes, these epicyclical gears have the characteristic to transmit an important torque with both small overall dimensions and relatively reduced level of vibration and noise. In this work, we present initially a plane model of the epicyclical double stages gear system while taking account of the bearings flexibility. Then, the error of transmission which is the main source of excitation of the train is evaluated. Finally, we develop the equation of total motion of the train to establish the vibratory and dynamic behaviour of the system studied.

2

Analytical Computation of the Mechanical Efficiency of Compound Mechanical Systems

100%

Kantchev K. , Baccar W. , Chaari F. , Haddar M.

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tom Vol. 33, No. 1

55-75

EN

In this paper, the mechanical efficiency of mechanical systems is discussed. The influence of the arrangement of the different components of the mechanism and the power distribution over the different modules on the efficiency is investigated. Revolute, slider and contoured joints are studied. Sliding and rolling frictions are taken into account in order to determine their mechanical efficiency. Two numerical examples of a crank-connecting rod mechanism and a cam follower system are presented and the evolution of their mechanical efficiencies over a cycle are computed.

3

Squeeze flow of concentrated suspensions of spheres in Newtonian or shear-thinning fluids

100%

Collomb J. , Chaari F. , Chaouche M.

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2003

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tom Vol. 8, no spec.

219-224

EN

The squeeze flow behaviour of concentrated suspensions of spheres in both Newtonian and shear thinning fluids is investigated experimentally. Analysing the evolution of the squeeze force as a function of time for different controlled velocities, the suspension is found to present two main flow regimes. The first regime is characterized by the situation in which the force decreases when the velocity decreases, which is expected and corresponds to a power-law fluid flow of the suspension. In the second regime the force increases when the velocity decreases which is an indication of solvent filtration through the particle skeleton that behaves then as a quasi-rigid porous media. It is found that the transition between the two regimes is a result of a competition between the viscous shear forces due the flow of the suspension and the damping force caused by the filtration of the fluid through the porous media made up by the particles. It is shown that the addition of a small amount (1000ppm) of a polymer (Xanthan) to the solvent significantly decreases the squeeze velocity for which we have fluid filtration.

4

Rheo-optical characterisation of linear low density polyethylene crystallization under shear

100%

Chaari F. , Chaouche M. , Benyahia l. , Tassin J. F.

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2003

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tom Vol. 8, no spec.

213-218

EN

Metallocene linear low density polyethylene (mLLDPE) crystallization under shear flow at controlled shear rates and above its crystallization temperature was investigated experimentally. The evolution of the material optical properties (turbidity, birefringence and dichroism) was monitored following a temperature jump from the melting point to a final crystallization temperature . These properties are discussed in terms of the evolution of the polymer semi-crystalline microstructure. In light of the optical properties evolution, the crystallization process can be split into three regimes (i) incubation phase in which small (compared to the light wavelength) crystalline nuclei spread over the medium, (ii) isotropic crystallite growth phase and (iii) anisotropic crystallite growth phase.

5

Modal analysis of gearbox transmission system in bucket wheel excavator

88%

Karray M. , Feki N. , Khabou M. T. , Chaari F. , Haddar M.

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tom Vol. 55 nr 1

253--264

EN

Planetary gears are widely used in modern machines as ones of the most effective forms of power transmission. In this paper, a special configuration of a gearbox composed of one stage spiral bevel gear and a two stage helical planetary gear used in a bucket wheel excavator gearbox is presented to investigate its modal properties. A lumped-parameter model is formulated to obtain equations of motion and the eigenvalue problem is solved. The modes are presented in low-frequency and high-frequency bands. Distributions of modal kinetic and strain energies are studied.