Papers by Keyword: Rheology

Abstract: Drilling fluid rheology is very important aspect for judging its suitability for the well-drilling operation. This study looked at how fly ash affected the rheological characteristics of drilling fluids that were based on water. Six different drilling fluid samples (combination of water-bentonite-fly ash) have been prepared: 4 samples without engine oil additives and 2 samples with engine oil additive. The shear stress between fluid layers vs. shear rate curves and the viscosity of fluid vs. shear rate curves have been plotted for the controlled shear rate application by rotational rheometer MCR 102 (Make: Anton-Paar Inc.). Curve fitting have been done successfully with the Herschel-Bulkley rheology model and various parameters have been obtained. It is found that addition of fly ash as well as additive oil imparts favorable rheology to water based drilling fluids.

Abstract: The phenomenon of siltation represents an enormous risk for the lifespan and safety of dams, and there are several methods for evacuating sediments, of which the hydraulic dredging technique is the most widely used. But during this operation there are load loss exists so it is necessary to find solutions to reduce it. The purpose of this work is to use the Aloe Vera gel as a load loss reducer during hydraulic dredging of dams. To carry out this study, a rheumatic characterization of dams sediments and dams sediments - Aloe Vera gel mixtures was carried out using a torque controlled rheometer (Discovery Hybrid Rheometer DHR2 from TA instrument) and a hydraulic study carried out on a closed-circuit installation comprising three pipes of different diameters and lengths, supplied by a centrifugal pump driven by a variable speed Diesel engine. The experimental work was carried in pipe of diameter D₁=36.16 mm and length L₁ = 12.24 m with the quantity of Aloe Vera 2 to 10 wt% and different speed of rotation of pump. The flow curves as a function of dose of Aloe Vera added to dam sediments were analysed by the Casson model. The calibration of installation has been fitted by the Blasius equation. The addition of Aloe Vera gel with a quantity range between 2 and 10 wt% to dams sediments of 40 wt% and 45 wt% induces an decrease in the yield stress and the viscosity infinite of dams sediments. The study also demonstrated that adding of 6 wt% of sodium tripolyphosphate to 40 wt% and 45 wt% dam sediments decreased the friction factor by 75% and 85% respectively

Abstract: Abstract. Additive manufacturing of concrete structures is a novel and emerging technology. Freecontouring in civil engineering, which allows for entirely new designs, is a significant advantage. Inthe future, lower construction costs are expected with increased construction speeds and decreasingrequired materials and workers. However, architects and civil engineers rely on a certain quality ofexecution to fulfil construction standards. Although several techniques and approaches demonstratethe advantages, quality control during printing is highly challenging and rarely applied. Due to thecontinuous mixing process commonly used in 3D concrete printing, it is impossible to exclude varia-tions in the dry mixture or water content, and a test sample cannot be taken as a representative samplefor the whole structure. Although mortar properties vary only locally, a defect in one layer duringprinting could affect the entire integrity of the whole structure . Therefore, real-time process monitor-ing is required to record and document the printing process.At the Bundesanstalt für Materialforschung und -prüfung (BAM) a new test rig for the additive man-ufacturing of concrete is built. The primary purpose is measuring and monitoring the properties of amortar during the printing process.The following study investigates an approach for calculating yield stress and plastic viscosity based onexperimentally recorded pressure data. The calculations assume that fresh mortar behaves as a Bing-ham fluid and that the Buckingham-Reiner-equation is applicable. A test setup consisting of rigid pipeswith integrated pressure sensors at different positions is utilized.Monitoring the printing process with different sensors is crucial for the quality control of an ongoingprocess.

Abstract: Addition of high percentage of palm stearin (PS) into a blend with high density polyethylene (HDPE) may result in the blend instability and poor flowability of the composite during injection moulding process. The undesirable effect of the PS addition arises from lack of interaction between the PS and HDPE matrix. To improve the interaction between the two components, a compatibilizer was added to the blend. The objective of this work is to study the effect of glycerol monostearate (GMS) compatibilizer concentration (1-5 wt%) on the HDPE-PS composite with PS content of 40 wt.%. The thermal properties of the HDPE-PS composite were characterized using torque analysis, differential scanning calorimetry (DSC) analysis and rheology analysis. It was found that melting temperature of the HDPE-PS composite decreases with GMS concentration. The presence of GMS in the HDPE-PS composite had improved composite flowability indicate suitability of the GMS as compatibilizer for the HDPE-PS composite.

Abstract: Metal injection molding (MIM) feedstock is composed of Cu powder and a complex binder system that consists of PA6, MgSt, and GMS with various solid loading (43-53vol%). Cu powders used are fabricated by gas and water atomization. Powder particle shapes used have spherical and dendritic shapes. Sphericity of particles can be identified by Scanning Electron Microscopy (SEM). A rheology test is used to ensure the optimum solid loading and investigate the influence of particle shape. The pseudo-plastic behavior of all the feedstock is exhibited by decreasing viscosity along with increasing shear rate for all working temperatures. In this study, rheological test result such as viscosity, flow activation energy, and flow behavior index of feedstock indicates that the optimum solid loading was selected as 43 vol%. Both gas and water atomized powders are desirable for MIM feedstock. According to the rheology behavior test, gas-atomized powders with spherical shape has better rheology stability than water-atomized powders with dendritic shape. The proper MIM feedstock was selected to solid loading 43 vol% with gas-atomized powders.

Abstract: Semisolid castings are usually produced using primary Al alloys to ensure significant mechanical performances. However, the need to increase the use of secondary alloys is becoming more and more urgent to reduce the carbon footprint of the manufacturing process. In fact, it is well known that the production of primary alloys is far more demanding in terms of energy and emissions than the recycling route. To extend the use of secondary alloys to semisolid processing, it is necessary to thoroughly understand their properties and how they can influence a material with peculiar properties as the semisolid one. Besides microstructural and mechanical features, the rheological behaviour also plays a major role when dealing with processing metals in the semisolid state. Therefore, in the present study, a rheological characterization of secondary AlSi7Mg commercial alloy was carried out and compared to that of the conventional primary alloy. In details, a different content of Fe, Cu and Mn was considered, as these impurities easily form primary intermetallic particles, which can remain dispersed in the liquid matrix of the semisolid metal. The aim of this work is to understand if this can affect the rheological properties of the considered semisolid alloy. Flow curves and yield stresses were obtained from the experimental results to compare the behaviour of the different alloys.

Abstract: Semisolid materials with a non-dendritic microstructure have a complex rheological behavior such as pseudo-plasticity and thixotropy. These properties affect filling and solidification processes during, casting; thus, simulation plays a vital role since it avoids limitations improving cast and production performance. In order to study and A356 aluminum semisolid alloy flow, a Computational Fluid Dynamics (CFD) software (ANSYS) is used to simulate the die filling process in a rectangular mold. Three non-Newtonian constitutive equations are modeled in this work: the Cross equation, the Power-law equation and the Carreau equation. The rheological parameters for each equation were obtained from experimental data reported in the literature. The results showed that the non-Newtonian models predicted better the filling behavior and the pressure distribution than the Newtonian model.

Abstract: It is fundamental in thixoforming to have a refined microstructure that, when heated to the semisolid state, consists of a mixture of small spheres immersed in liquid as this ensures the best rheological properties. The present work therefore aims to analyze the rheological behaviour of aluminum-silicon-copper alloys, namely, Al5Si2.8Cu, Al6Si2.8Cu and Al7Si2.8Cu. The alloys were produced by conventional casting and then deformed by ECAP in one pass in a die containing two channels of the same cross-sectional area forming an angle of 120°. After being processed by ECAP, the alloys were heated to semisolid temperatures, i.e., temperatures corresponding to a solid fraction of 45 %, and kept in the semisolid state for 0, 30 and 90 s, after which they were subjected to hot compression tests. The structures of the three alloys had an excellent response to recovery and recrystallization mechanisms, with refined microstructures that led to the formation of very fine spheres immersed in liquid in the semisolid state. The best rheological behaviour was obtained for the Al5Si2.8Cu alloy, which had an apparent viscosity of the order of 10³ Pa.s. The findings suggest that this simple ECAP process is a promising route for the production of semisolid feedstock for use in thixoforming.

Abstract: Rotational rheology was used to analyze the performance of polypropylene (PP) composites reinforced with date palm nanofiber (DNF) in the molten state in this study. In the first stage, mechanical ball milling was used to obtain date nanofillers with average filler sizes ranging from 30–110 nm in width and 1–10 mm in length. Dry blending technique was used to reinforce this filler to the polypropylene in the 1-5wt. % loading. The resulting PP/DNF biocomposites were subsequently tested using a rotating rheometer with a 25 mm parallel plate geometry. The broad range of angular frequency from 0.1 rad·s⁻¹ to 100 rad·s⁻¹ was applied to study their complex viscosity (η*) at a fix strain (1%). The decrease in complex viscosity with angular frequency in all the samples was observed compared to the neat PP. The complex viscosity of the neat PP and the 5 wt.% of filler samples at 0.1 rad·s⁻¹ frequency was found to have 18170 Pa. s and 5335 Pa. s, respectively. Therefore, this analysis revealed that this biocomposites exhibits typical viscoelastic behavior of entangled polymeric liquid.

Abstract: This paper presents research on the rheology of earth-based composites for Additive Manufacturing (AM) The study experiment setup is based on using different types of natural fibers with earth hydraulic binders through a pneumatic extrusion system of a 3axis printing machine. The ingredients of the composites are eco-friendly, locally available, inexpensive, and driven from recycled sources. The line tests have been done to improve important parameters related to extrudability, plasticity, and fluidity of the material composite through the printing process.