Numerical study ofthe mechanical behaviour of railway wheels containing tearing on the tread.

ABSTRACTWith the intention of ensuring security and diminishing the costs of service in the railway systems, it is necessary to characterize the mechanical behavior of the zone containing tearing of metal caused by a manufacturing defect which can be at the origin of breaks. The influence of these defects, present in the metal of the wheel was studied by simulating three geometrical forms: circular defect, elliptical defect and any form defect. The constraints and distortions were analyzed in the immediate neighborhood of these defects. The Calculations were performed for a level of load corresponding to the weight of the trailer of the new railcars in Algeria and to the assistant of a code of calculation by finished elements (ANSYS)

Dérive temporelle post-irradiation dans les dosimètres MOS de rayonnement

The properties of the post-irradiation annealing in MOS transistors used as dosimeter are studied. It is shown that the observed shift, probably caused by tunnel injection of electrons from the transistor channel, is a decreasing function of the insulator thickness. The limits of such a dosimeter when a very low dose rate is measured are evaluated.Les propriétés de la dérive post-irradiation dans les transistors MOS utilisés comme dosimètres sont étudiées. Il est montré que cette dérive, probablement due à une injection tunnel des électrons du canal, est une fonction fortement décroissante de l'épaisseur de la grille. Une évaluation des erreurs commises lors de la mesure de faibles débits de dose permet de définir les limites d'utilisation de ce type de dosimètre

Cost optimization of reliability testing by a bayesian approach

The Bayesian approach is a stochastic method, allowing to establish trend studies on the behavior of materials between two periods or after a break in the life of these materials. It naturally integrates the inclusion of the information partially uncertain to support in modeling problem. The method is therefore particularly suitable for the analysis of the reliability tests, especially for equipment and organs whose different tests are costly. Bayesian techniques are used to reduce the size of estimation tests, improving the evaluation of the parameters of product reliability by the integration of the past (data available on the product concerned) and process, the case “zero” failure observed, difficult to treat with conventional statistical approach. This study will concern the reduction in the number of tests on electronic or mechanical components installed in a mechanical lift knowing their a priori behavior in order to determine their a posteriori behavior

Electrical properties of MOS radiation dosimeters

MOS transistors are used for radiation dosimetry. The sensitivity obtained is ranging between 20 mV/ Gray (SiO2) and 1,5 V/Gray (SiO 2). Good linearity and stability of the transistor response is obtained

Methods of the rational choice of a labyrinth seal design for gas pumping units

This present paper describes a method of improving the labyrinth seal design by the development of three-dimensional parametric computer of its model and an anal-ysis of its work for gas pumping units (GPU) using the finite-element method. The authors have improved design labyrinth seal of the GPU according to the criterion of minimum pressure in the last gap by Gauss-Seidel method of optimization, which will increase GPU operational efficiency by reducing flowing medium at various operating modes of GPU. It is shown that change of geometrical sizes and form of creating more compact part of labyrinth seal with inclination them toward greater pressure for an angle of 80° decrease leakages of gas, that in same time considerably influences on the expense of working environment on the output of labyrinth sea

Détermination expérimentale des paramètres des transistors MOS

We present experimental methods to determine the MOS transistor parameters : effective channel. length, carrier mobility, mobility roll-off coefficient, series drain and source resistances. They are deduced from i) the output conductance measurement, at low drain bias, on a set of MOS transistors with different channel length, and ii) the comparison of the transfer characteristics in the normal and in the reverse configuration, i.e. by inversion of the drain and source electrodes.On propose des méthodes expérimentales propres à déterminer les paramètres des transistors MOS : longueur effective du canal, mobilité des porteurs, potentiel transversal de réduction de mobilité, résistances en série dans la source et le drain. Elles sont basées d'une part sur la mesure des conductances de sortie à faible tension drain-source effectuée sur des transistors MOS de même géométrie mais ayant des longueurs de canal différentes et, d'autre part, sur la comparaison des caractéristiques de transfert courant-tension en régime de non-pincement, en configuration normale et en configuration de source et drain inversés