A new way to include the grain shape in texture simulations with the Taylor model
The use of the Hall-Petch relation in texture simulations with the Taylor-Bishop-Hill model is proposed as a mean to take into account grain shape effect. The results are compared with those obtained with the usual and relaxed constraint Taylor model for a simple texture and the consequences for the anisotropy coefficient are investigated On propose d'utiliser la relation de Hall-Petch dans les simulations de texture a l'aide du modele de Taylor-Bishop-Hill pour prendre en compte la forme des grains. Comparaison des resultats avec ceux du modele de Taylor classique ou relaxe dans le cas d'une texture simple; consequences pour le coefficient d'anisotropie
Some applications of the Taylor theory of polycrystal plasticity
The Taylor theory of polycrystal plasticity was applied to three-axial deformation accomplished by glide on (111) [110] or (110) [111] glide systems. The orientation dependence of the Taylor factor was used to calculate the angular dependence of the relative strength of a textured material. The angular dependence of the strain ratio R — calculated from the minimum value of the Taylor factor — was compared with the measured strain ratio. The orientation changes of the crystallites of a polycrystalline aggregate after 1% plastic deformation were calculated and compared with experimental values. The orientations which are deformed without orientation changes were calculated and compared with those of maximum orientation density found by a three-dimensional texture analysis of cold rolled copper and iron. The dependence of the rotationless orientations on the axis ratio of the deformation tensor was calculated. This allows suggestions to be made on the dependence of the rolling textures on the lateral broadening of the sheet during rolling. 
 
 
 
Die Taylor-Theorie der Vielkristallplastizitat wurde auf dreiachsige Verformungszustande und Gleitung auf (111) [110]- oder (110) [111]-Gleitsystemen angewandt. Aus der Orientierungsabhangigkeit des Taylor-Faktors wurde die Winkelabhangigkeit der relativen Festigkeit eines Texturmaterials berechnet. Die Winkelabhangigkeit des R-Wertes der plastischen Verformung — berechnet aus dem Minimalwert des Taylor-Faktors — wurde mit den gemessenen R-Werten verglichen. Die Orientierungsanderungen der Kristallite eines vielkristallinen Aggregates nach 1% plastischer Verformung wurden berechnet und mit experimentellen Werten verglichen. Diejenigen Orientierungen, die sich ohne Orientierungsanderung verformen, wurden berechnet und mit den Orientierungen maximaler Orientierungsdichte verglichen, die sich aus der dreidimensionalen Texturanalyse kaltgewalzter Kupfer- und Eisenbleche ergaben. Die Abhangigkeit der drehungsfreien Orientierungen vom Achsenverhaltnis des Deformationstensors wurde berechnet. Daraus ergeben sich Schlusfolgerungen uber die Abhangigkeit der Walztexturen von der relativen Breitung des Bleches wahrend der Walzung.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.