Comparative Study to Optimize Surface Roughness of the Titanium Alloy Ti-6Al-4V by Applying Taguchi, RSM and TLBO Methods

Titanium alloys are used in aeronautics and the shipbuilding industry for their good intrinsic properties, namely low density (40% less than steel), very good mechanical properties and resistance to corrosion. The purpose of this study is to optimize the cutting conditions during the turning of Ti-6Al-4V titanium alloy with Minimum of Quantity of Lubrication (MQL) conditions leading to minimize the surface roughness (Ra). The tests were carried out according to a Taguchi L18 design plan by varying four input factors namely: the cutting speed, the feed rate, the depth of cut and the cutting tool material (coated carbide with (PVD) (GC1125) and uncoated carbide (H13A)). Analysis of variance (ANOVA) was used to found the contribution of each factor and to determine which parameters had a significant influence on the surface roughness. The treatment of the results made it possible to propose a mathematical model, which allows predicting Ra. In addition, Taguchi Signal/Noise (S/N) analysis was used in order to optimize the cutting conditions permitting to minimize Ra. The Desirability Function (DF) was also determined. In addition, the obtained results were compared to the one determined using Response Surface Methodology (RSM) and Teaching and Learning Based Optimization (TLBO). It is important to note that the TLBO method gave a very satisfactory result

Oxide charges densities determination using charge-pumping technique with BTS in MOS structures

A New electrical method, using charge-pumping (CP) technique under bias thermal stress (BTS), has been described in this paper. This technique is based on the charge-pumping measurement which in turn used to extract the flat-band voltage before and after an applied bias voltage at high temperature. The obtained flat band voltage shift, that is due to redistribution of the mobile ionic charges, or to generation of the oxide trapped charge or both, may be used to determine their densitie

Analyse de l'impact des paramètres de coupe et des vibrations sur la rugosité des pièces usinées en tournage à partir de la méthode de régression linéaire multiple

La rugosité des surfaces des pièces usinées par tournage joue un très grand rôle sur la qualité du produit fini. Notre étude consiste à développer un modèle basé sur des expériences pour la prédiction de la rugosité. Beaucoup de paramètres influent sur la rugosité d'une façon directe ou indirecte, à savoir les paramètres du régime de coupe tels que l'avance par tour, la vitesse de rotation, la profondeur de passe et les efforts de coupe générés aux contacts outil-pièce, sans oublier les vibrations de l'outil dues aux phénomènes de coupe. Pour mettre en évidence l'influence de tous ces paramètres, des expériences sont réalisées selon un plan factoriel. La détermination du modèle est obtenue par la technique de régression linéaire multiple, sa validation est confirmée par la comparaison de la rugosité obtenue par le modèle et la rugosité mesurée. L'application de cette technique statistique pour la prédiction de la rugosité montre sa fiabilité car l'erreur entre la valeur expérimentale et la valeur calculée par le modèle est négligeable

Modelling of chloride migration in cementitious materials including thermodynamic equilibria

In this paper, a multispecies approach for the reactive transport modelling in cementitious materials is proposed. It considers the thermodynamic equilibria in the material during the transport that reflect the liquid – solid interactions and the dissolution/precipitation of solid phases (minerals): dissolution and precipitation of Portlandite and C-S-H. The ion fluxes during the transport are calculated using the Nernst-Planck equation that considers the natural diffusion under a concentration gradient, the migration under an electrical field, and the chemical activity. The model proposed is applied to simulate the standard chloride migration test on two cement pastes. The first paste is based only on Portland cement, while the second paste is composed of fly ash. Numerical results of fluxes of Cl-, Na+ and K+ at the steady state are used to calculate the corresponding effective ion diffusion coefficients in the material studied