scholarly journals L-Box Form Filling of Thixotropic Cementitious Paste and Mortar

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1760
Author(s):  
Mareike Thiedeitz ◽  
Nasime Habib ◽  
Thomas Kränkel ◽  
Christoph Gehlen
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Rheological Parameters ◽  
Empirical Equations ◽  
Dynamic Yield Stress ◽  
Shear Rates ◽  
Flow Length ◽  
Dynamic Yield ◽  
Fast Flow

Rheological properties of cementitious pastes and mortar affect the casting, placement, and setting properties of fresh concrete. Fundamental rheological knowledge thus helps in predicting concrete flowability and workability. Empirical equations correlate actual rheological parameters based on physical material characteristics to workability tests. Still, these equations generally only take the dynamic yield stress of the material into account. This is not sufficient for thixotropic cementitious pastes or mortars, which possess structural buildup at rest. Workability predictions regarding the flow of concrete are thus more complicated with thixotropic materials. During form-filling in L-shaped formworks, the flow velocity of concrete slows down, wherefore rheological parameters change with time. At initial fast flow, high shear rates without structural buildup can be assumed. Dynamic yield stress and a steady state viscosity thus are proper parameters for empirical equations describing concrete flowability. During low shear rates, partial structural buildup takes place. Viscosity and yield stress increase due to agglomeration and affect the flowability of concrete tremendously. Rheological parameters of various cementitious pastes and mortars varying in their solid volume fraction and flowability were investigated in a vane-in-cup rheometer. The workability of the same mixtures was investigated by measuring the flow length in an L-shaped formwork. The effect of yield stress, viscosity, and thixotropic structural buildup on flow length was investigated. Subsequently correlations and discrepancies between flowability parameters and workability equations were analyzed.

Dispersion of solids in fracturing flows of yield stress fluids

2017 ◽  
Vol 830 ◽  
pp. 93-137 ◽  
Author(s):  
S. Hormozi ◽  
I. A. Frigaard
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Three Dimensional ◽  
Process Variations ◽  
Model Framework ◽  
Shear Rates ◽  
Low Viscosity ◽  
High Shear Rates ◽  
Solids Concentration

Solids dispersion is an important part of hydraulic fracturing, both in helping to understand phenomena such as tip screen-out and spreading of the pad, and in new process variations such as cyclic pumping of proppant. Whereas many frac fluids have low viscosity, e.g. slickwater, others transport proppant through increased viscosity. In this context, one method for influencing both dispersion and solids-carrying capacity is to use a yield stress fluid as the frac fluid. We propose a model framework for this scenario and analyse one of the simplifications. A key effect of including a yield stress is to focus high shear rates near the fracture walls. In typical fracturing flows this results in a large variation in shear rates across the fracture. In using shear-thinning viscous frac fluids, flows may vary significantly on the particle scale, from Stokesian behaviour to inertial behaviour across the width of the fracture. Equally, according to the flow rates, Hele-Shaw style models give way at higher Reynolds number to those in which inertia must be considered. We develop a model framework able to include this range of flows, while still representing a significant simplification over fully three-dimensional computations. In relatively straight fractures and for fluids of moderate rheology, this simplifies into a one-dimensional model that predicts the solids concentration along a streamline within the fracture. We use this model to make estimates of the streamwise dispersion in various relevant scenarios. This model framework also predicts the transverse distributions of the solid volume fraction and velocity profiles as well as their evolutions along the flow part.

Yield Stress of Emulsions and Suspensions as Measured in Steady Shearing and in Oscillations

2008 ◽  
Vol 18 (4) ◽  
pp. 44790-1-44790-8 ◽  
Author(s):  
I. Masalova ◽  
A.Ya. Malkin ◽  
R. Foudazi
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Yield Stress ◽  
Flow Curves ◽  
Dynamic Yield Stress ◽  
Shear Rates ◽  
Meaningful Material ◽  
Dynamic Yield ◽  
Steady Shearing ◽  
Concentrated Emulsions

Abstract The yield stresses of five samples (two highly concentrated emulsions, two Kaolin dispersions and mayonnaise) were determined in two ways. In one case, steady shear experiments were performed over a range of incrementally decreasing shear rates. The resulting flow curves, plotted as shear stress against shear rate, clearly showed the existence of a yield stress for each sample, the Herschel-Bulkley model being fitted to obtain values. In the second case, oscillatory amplitude sweeps were performed at three frequencies, and the “dynamic yield stress” was defined as the stress at which deviation from linearity occurred; this procedure has often been used to determine the yield stress of emulsions. It was found that the dynamic yield stress is frequency dependent, and cannot therefore be thought of as physically meaningful material property. At no frequency did the dynamic yield stress correlate with the yield stress obtained from the flow curves.

THE STRESS-STRAIN RELATIONSHIP AND THE DYNAMIC YIELD STRESS IN ELECTRORHEOLOGICAL FLUID UNDER A MODIFIED CONDUCTION MODEL

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1456-1462
Author(s):  
CHUNRONG LUO ◽  
HONG TANG ◽  
XIANGYANG GAO ◽  
JIANBO YIN ◽  
XIAOPENG ZHAO
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Electrorheological Fluid ◽  
Dipole Approximation ◽  
Approximation Model ◽  
Stress Strain ◽  
Conduction Model ◽  
Dynamic Yield Stress ◽  
Static Yield ◽  
Dynamic Yield

By using a modified conduction model and the dipole approximation model respectively, we simulate the stress-strain curve and evaluate the dynamic yield stress through an ideal microstructure model of electrorheological fluid. The static yield strain is larger in our modified conduction model than in the dipole approximation model. Besides, the dynamic yield stress and static yield stress nearly linearly vary as volume fraction in the dipole model, while in our modified model they both exhibit a maximum at about volume fraction ϕ=0.45. Interpretation about these results is associated with the conduction effect and the inter-chain interactions.

scholarly journals Влияние гигантской магнитострикции на динамический предел текучести в условиях высокоскоростной деформации

2021 ◽  
Vol 63 (12) ◽  
pp. 2070
Author(s):  
В.В. Малашенко
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Yield Stress ◽  
High Strain ◽  
Dynamic Yield Stress ◽  
High Strain Rate Deformation ◽  
Dynamic Yield ◽  
Giant Magnetostriction

The high-strain rate deformation of crystals with giant magnetostriction is theoretically analyzed. It is shown that giant magnetostriction has a significant effect on the dynamic yield stress of crystals.

scholarly journals Effects of Silicone Oil Viscosity and Carbonyl Iron Particle Weight Fraction and Size on Yield Stress for Magnetorheological Grease Based on a New Preparation Technique

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1778 ◽  
Author(s):  
Kejie Wang ◽  
Xiaomin Dong ◽  
Junli Li ◽  
Kaiyuan Shi ◽  
Keju Li
Keyword(s):  
Yield Stress ◽  
Carbonyl Iron ◽  
Silicone Oil ◽  
Weight Fraction ◽  
Iron Particle ◽  
Preparation Technique ◽  
Oil Viscosity ◽  
Dynamic Yield Stress ◽  
Carbonyl Iron Particle ◽  
Dynamic Yield

This paper investigated the effects of silicone oil viscosity (SOV) and carbonyl iron particle (CIP) weight fraction and size on dynamic yield stress for magnetorheological (MR) grease. The MR grease samples were prepared using orthogonal array L9 on the basis of a new preparation technology. The shear rheological tests were undertaken using a rotational shear rheometer and yield stress was obtained based on the Bingham fluid model. It was found that CIP fractions ranging from 65 wt% to 75 wt% and SOV varying from 50 m2·s−1 to 1000 m2·s−1 significantly affect the magnetic field-dependent yield stress of MR grease, but the CIPs with sizes of 3.2–3.9 μm hardly had any influence based on the analysis of variance (ANOVA). In addition, the yield stress of MR grease mainly depended on the CIP fraction and SOV by comparing their percent contribution (PC). It was further confirmed that there were positive effects of CIP fraction and SOV on yield stress through response surface analysis (RSA). The results showed a high dynamic yield stress. It indicated that MR grease is an intelligent material candidate which can be applied to many different areas requiring high field-induced rheological capabilities without flow for suspension. Moreover, based upon the multivariate regression equation, a constitutive model was developed to express the function of the yield stress as the SOV and fraction of CIPs under the application of magnetic fields.

The Spall Strength and Dynamic Yield Stress of Hafnium

2019 ◽  
Vol 45 (1) ◽  
pp. 27-30 ◽  
Author(s):  
A. M. Molodets ◽  
A. S. Savinykh ◽  
A. A. Golyshev ◽  
G. V. Garkushin
Keyword(s):  
Yield Stress ◽  
Spall Strength ◽  
Dynamic Yield Stress ◽  
Dynamic Yield
Sign in / Sign up

Export Citation Format

Share Document