Papers by Keyword: Shear Stress

Abstract: The article is devoted to the analysis of the composition and properties of the materials and liquids during transportation using pipeline and shows that in order to increase the efficiency of hydraulic transport systems in mining a transition to the transportation of slurries with a high concentration of solids in the slurry flow is necessary. Experimental studies have shown that slurry tailings of gold-containing ore with mass concentrations of more than 55 % are viscoplastic fluids. Experiments on a rotational viscometer allowed us to establish the main rheological characteristics of the studied slurries – shear stress and the dynamic effective viscosity. It has been established that over the entire range of concentrations from 55 to 65 %, the flow of slurries is described by the Bingham rheological equation. Experimental studies of hydraulic transport performed on a laboratory setup with a pipeline diameter of 50 mm confirmed the results obtained on a rotational viscometer. The curved of mixture stream is inclined straight lines that are cut off on the axis of the head in the sections, which determine the initial hydraulic slope corresponding to the yield shear stress on the rheological curves. According to the results of the experiments, a method has been developed for calculating the hydraulic transport of high concentrated slurries of tailings of gold-bearing ore. Calculations showed that in a given range the performance of the hydrotransport system and the mass concentration of the solid phase pressure losses vary from 11 to 84 m of water column/m. Head loss values increase with the increasing concentration. A sharp increase in the head loss occurs in the concentration range from 60 to 65 % and higher.

Abstract: A study on the Saint-Venant principle implementation for a rigidly clamped I-beam loaded with various loads at the free end was carried out. When using the software package LIRA SAPR, the tangential stresses perturbations zones are determined in order to compare their distribution with the materials resistance solution.

Abstract: The treatment of aortic aneurysm varies according to each patient. Stent implantation is one of many methods used to stabilize diseases. The information obtained from hemodynamic parameters in the pathological aorta with stent could help doctors in choosing the treatment before the surgery. In this context, the numerical simulation of fluid dynamics is an essential tool that can give us more detailed information that could be exploited by surgeons to find appropriate solutions to some pathologies. In this work, a study of two models of aortas: with and without stent was presented. A comparison of the results of changes in pressures and shear stresses of aortas in systolic and diastolic phases was discussed. The obtained results show a nearly similar tendency of variation for both models, which justifies the effectiveness of the type of stent chosen and its effect on the improvement of the blood flow. The methodology used in this work has revealed the detailed and necessary information for both cases studied and has shown the interest of the numerical tools for diagnosis and surgery.

Abstract: Magnetic fluid or called ferro-fluid is such kind of magnetic nanomaterials, which is stable of solid-liquid two phase colloidal solution composited by magnetic nanoparticles coated by surfactant and highly disperse in a carrier liquid. The basis of magnetic fluid widely applied mainly is due to their unique magnetic properties and rheological properties, which enable its action as intelligent control materials in the magnetic field so as to achieve the goal of magnetic liquid dynamic seal, magnetic damping vibration and so on. In our recent research, the water-based magnetic fluid was synthesized using a co-precipitation method and its magnetorheological properties were studied. During the process, the magnetorheological properties of stable water-based magnetic fluids were determined by magnetic rheometer. The results show that the shear-thinning behavior of magnetic fluids was observed both in the absence and presence of magnetic field. However, there was a remarkable magnetoviscous effect with magnetic field function and the unexpected variation of shear stress was related to the chain aggregation. Furthermore, the constitutive equation of water-based magnetic fluid at a low magnetic field was discussed.

Abstract: In a previous study, we presented new method measurement rheological properties of hydrophobized plaster in dependence of hardening time. Influence of external temperature on pozzolana plaster is analyzed in this paper, especially plasticity and workability of paste. Main aim of rheological test is determination of flow curves, obtained by applying a succession of constant strain rates for short times at the temperature 10°C and 30°C. Base on the performed experiments, it can be concluded that the temperature have very significant influence on rheological properties of plasters. With an increase in temperature, the application time of the mixture is shorter, from hour to minutes. A comparative measurement with pure lime plaster was done as well.

Abstract: The influence of time on rheological properties of modified lime plaster is analyzed in this paper. Effect of composition of mixture is examined as well. Especially changes of paste due to hydrophobic and pozzolanic admixture. Main aim of rheological test is determination of flow curves, obtained by applying a succession of constant strain rates for short times. Base on performed experiments, it can be concluded that hydrophobic admixture eliminated influence of pozzolana. Also both time and temperature caused significant changes in rheological properties. Increasing values decreases the flow characteristic of the plaster. A comparative measurement with pure lime plaster was done as well.

Abstract: The purpose of this study is to investigate the rheological properties of alkali-activated slag prepared as a paste modified by various amount of polymer admixtures. Four commercial admixtures VINNAPAS^® 5023 L, 5111 L, 7016 F and 7220 E were used as polymer admixture in this study. These admixtures were incorporated to alkali activated slag pastes in quantities between 0.5 and 2% by mass of slag. Rheological properties as shear stress and viscosity of fresh pastes were examined by Discovery HR-1. Another main focus of this paper is the effect of selected admixtures on the heat of hydration of an alkali activated slag. Results indicate that addition of polymer admixtures affects the viscosity of the pastes and hydration process.

Abstract: UHPC (ultra-high-performance concrete) is one of the essential elements in the development and research of new modern concrete structures. It is a material showing all the positive qualities in terms of the design efficiency and construction process. In this paper, we analyze the behavior of prestressed UHPC I-beam with lightened web that is loaded by four-point bending test. Two variants of I-beam were used for the analysis. The first variant is beam with a continuous thin web and the second variant is beam with lightened web, which is analogous to castellated steel I-profiles, commonly used types of steel beams with larger span. Although these are relatively small specimens, light beam analysis can be extrapolated for large span structures, especially bridges. In case of structures of larger magnitude with precast members of UHPC, a certain amount of discontinuous action cannot be avoided, which is the case of using a lightened beam with openings across the entire height of the web. Application of prestressed tendons ensures sufficient resistance for bending action; members are designed so failure occurs by shear response.

Abstract: This paper deals with non linear elastic materials for which not all the stresses are admis-sible but only those which belong to the stress range, i.e. a closed and convex subset of the spaceof all symmetric tensors. The constitutive equation that has been formulated and explicitly solved issufficiently general to include, besides the so-called masonry-like materials, many others whose stressrange is obtained experimentally or is theoretically defined. The model, implemented into the finiteelement code MADY, has been used to analyze a masonry panel under a bi-directional monotonicallyincremental load and the obtained numerical results have been discussed.

Abstract: Rotational rheometer has been widely used in studying rheological properties of materials. However, the conventional rheological measurements may not be applicable for some non-traditional materials with characteristic properties. Polycarbosilane (PCS) is an oligomer and in the form of solid state at room temperature. A large amount of air bubbles are evolved during the heating process of PCS, which is extremely harmful for rheological measurements of PCS melt and detrimentally influences the accuracy of rheological data. In this work, a series of PCS raw samples were pretreated with different heating processes by the advanced rheometric expansion system at 315°C before the rheological measurements at 295°C. The softening point temperatures and molecular weight distributions of different PCS samples were obtained before and after the preheating processes. The experimental data collected with the in-situ preheating and ex-situ preheating for 1 h were compared.