EIGENVALUE REANALYSIS OF STRUCTURES USING PERTURBATIONS AND PADÉ APPROXIMATION

Based on the usual perturbation and Padé approximation, a new eigenvalue reanalysis method for modified structures is developed in this paper. By this method, the accuracy of the eigenvalues and varying ranges of the parameters of the structures are improved. As an application of the method, a numerical example is given and the second-order perturbation method and the proposed method are compared in the accuracy of eigenvalues and range of parameters. The results show that the present method is effective.     

Étude expérimentale du comportement dynamique des matériaux

Experimental characterisation of materials under dynamic loading. This paper is specially dealing with dynamic testing and in particular the experimental characterisation of materials under dynamic loading. We shall focus on the SHPB (Split Hopkinson Pressure Bar) system because of its frequent use in a range of strain rates from 50/s to 5000/s which corresponds to the strain rates involved in most of civil industrial applications. The limitations of this system and its special advantages will be recalled. Some typical results obtained for various materials and small structures will be shown.     

RAYLEIGH-BÉNARD-MARANGONI INSTABILITIES DURING EVAPORATION OF AQUEOUS ALCOHOL SOLUTIONS,DETECTED BY PYROELECTRIC SENSORS

Abstract

A simple pyroelectric sensor is presented for on-line monitoring of Rayleigh-Bénard -Marangoni convective instabilities in methanol, ethanol and isopropanol aqueous solutions, caused by alcohol evaporation from the free surface of the liquid. The signals measured at the liquid-substrate interface represent thermal fluctuations of the order of 10^?2 K, having a frequency spectrum between 0.08 Hz and 0.4 Hz. The numerical estimation of the Rayleigh and Marangoni numbers leads to the conclusion that the latter is dominant in the conditions of the experiment. The amplitude and duration of the thermal noise are investigated as a function of alcohol concentration. An attempt is made to determine characteristic invariant quantities.     

Contrôle des écoulements appliqué a l'automobile. État de l'art

The control of the flows forms the basis for the work of development in automotive aerodynamics. Apart from the traditional techniques usually used, many experimental techniques often developed for aeronautics can constitute effective means of reduction of consumption, noise and stains. These techniques can also be used to improve the safety and the dynamic stability of the vehicles at the time of the phases of crossing, overtaking, entry or exit of tunnel with cross-wind. This article constitutes a state of the art of the new techniques which enable to control the flow and the position of separations lines. For each solution, the experimental conditions are recalled and the principal results presented.     

Évolution dimensionnelle des aciers martensitiques : étude expérimentale et modélisation

The microstructural causes of the dimensional change of a martensitic 100Cr6 bearing steel during an isothermal treatment are studied. On the one hand, the carbon of the supersaturated martensitic solid solution precipitates as carbides, inducing a shrinkage governed by the martensite carbon content as a function of time. On the other hand, the residual austenite decomposes, which leads to an expansion, depending on the austenite content as a function of time. These laws can be derived from experiments such as thermo-electric power measurements and X-ray diffraction. At a microscopic scale, the local dimensional variations are assessed and introduced as eigenstrains, into a homogenisation model taking into account the elastic stiffnesses and morphological arrangement of the different phases. The as-calculated dimensional variations are in agreement with the experimental measurements.     

Étude des transformations microstructurales survenant lors de l'endommagement par frottement sec d'un couple fonte/acier

In this study we will show the limits of use of the pair made of superficially quenched by induction 35CD4 steel and bainitic iron with spheroidal graphite during dry friction. This limit of use is the result of a quick deterioration of the shaft. The tribological mechanisms which took part in the shaft's damage are to be linked to the microstructural transformations.     

Étude analytique et expérimentale du perçage de plaques minces en carbone/époxy

Theoretical and experimental study of the drilling of thin carbon/epoxy plates. Drilling thin carbon/epoxy plates creates damages. The main damage is the delamination of the last laminate plies. This paper deals with the determination of the critical drilling force which is determined as a function of the location of the drill tip in the laminate. First, an analytic modelling and experimental procedure are presented and the study synthesis shows the interests and the limits of this modelling. Lastly, relation between trust force and cutting conditions is proposed.     

État de l'art sur l'accessibilité et l'étude de l'ergonomie en réalité virtuelle

The development and the use of DMU (Digital Mock-Up) and virtual reality in industry enhance the design of new tools for testing and validating virtual prototypes. This paper deals with the problem of mountability and maintenability analysis of parts in encumbered environments by virtual human operators (namely, manikins). This analysis is performed in relation with some ergonomic constraints from the operator point of view. There exist two main methods for performing such task. The first one consists in immersing the designer in the virtual world of the mechanical system; the second one takes advantage of a semi-automatic approach where the manikins are controlled through a predefined kinematical and ergonomic behaviour. We propose a comparison of these two methods.     

Étude du bruit dit de graillonnement dans les boı̂tes de vitesses automobiles

In a car, acoustic comfort has become a sales point. Due to the fact that the main noises have been reduced, the secondary sounds which could not be heard before suddenly became annoying. Such is the case of rattle noise, caused by repeated impacts between unloaded gears in the gear box, as they are driven by the engine acyclism. This publication presents a new method of study of the rattle noise. Our test bench is original, given that the gear box is not operated but is submitted to small angular oscillations. This allows us to control the angular acceleration applied on the primary shaft. We first distinguished and reviewed various kinds of rattling depending on the acyclism level produced. Then, we simulated real engine excitation by applying an acceleration made up of a sum of harmonics rather than a simple sine. Our aim being to measure the influence of the spectral composition and the waveform of the gear box input torque on the rattle threshold.     

Le contrôle non destructif des matériaux composites à matrice métallique renforcés par particules. État de l'art

The development of metal matrix composite reinforced by particles is possible only through the control, if possible “on-line”, of these materials. We have restricted our paper to non-destructive tests only. Out of these test we have considered three traditional, or in full expansion, techniques such as ultrasonic waves, acoustical microscopy and X-ray tomography. These three techniques give quite good results. A fitting model for interpretation of these results is a mixing linear law. From this fit one can qualify the product material. But the eventuality of porosities may disturb the analysis results. So the quantification of this type of defects is not studied in this paper.     

Étude bidimensionnelle du positionnement relatif des éléments de mécanismes avec jeu dans les liaisons par une méthode d'optimisation

One of the main objectives of engineers is the improvement of the performances of mechanisms and their reliability. The goal of this study is to propose a new method of static analysis in order to determine the arrangement of the various components of planar mechanisms subjected to mechanical loadings. The study takes into account the presence of linkage clearance and allows for the computation of the small variations of the parts position compared to the large amplitude of the movements useful for the power transmission. The method is based on the minimization of the potential energy of the whole mechanism. The results obtained from several simulations show the effectiveness of the method. The applications can deal with the numerical simulation of contacts between solids in finite element codes.