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HYPOTHESIS: The measurement of interfacial viscoelastic moduli provides information on the ability of surface-active agents to texture the interface. However, the contribution of the bulk rheology cannot be ignored in particular when the continuous phase exhibits a gel-like behavior, even with low modulus.EXPERIMENTS: Between 2 and 6 g/L, κ-carrageenan aqueous solutions have no significant activities at interfaces. At low concentrations or high temperatures, they behave like Newtonian liquids. Upon heating or cooling, a reversible liquid/gel transition appears with a hysteresis where the rheological behavior can be easily modulated by adjusting κ-carrageenan concentration. The frequency dependence of bulk and interfacial viscoelastic moduli are determined using a conventional shear rheometer and a drop tensiometer with a polyisobutene oil, respectively.FINDINGS: The effect of concentration and temperature is analyzed and the frequency dependence of interfacial moduli is correlated with those of the bulk. In presence of a gelled κ-carrageenan solutions, an elastic behavior of the interface appears and strengthens as the elastic modulus of the suspended phase is high. It turns out that the oscillating pendant drop method could be a sensitive indicator of the presence of very weak gels, even hardly detected by a shear classical rheometry.

In the present research, we evaluated the printability of inks that were formulated using an acrylate-endcapped urethane-based poly(ethylene glycol) hydrogel precursor (AUP) and a silicate-based nanoclay Laponite. Flow characterization of the AUP/ Laponite hydrogel inks revealed both yielding and shear thinning behavior, strongly dependent on the concentrations of the AUP and Laponite. In order to have a better insight into printability, the flow behavior along the cross section inside the printing needle was evaluated from the experimental shear flow data. The maximum stress values estimated inside the needle were applied to investigate the structural recovery of the inks using oscillatory rheology. Close analysis of the shear modulus recovery of the AUP/Laponite inks revealed a biexponential behavior, indicating a two-step recovery mechanism. The recovery mechanism is composed of fast and slow recovery steps and it appears that the shape fidelity after ink deposition is primarily controlled by the fast recovery contribution. Optimal printability was achieved for the ink formulation with the shortest characteristic time as well as a high modulus (>500 Pa) compared to the inks which could not be printed into well-defined structures. In the final part, cell interactivity of the three-dimensional (3D)-printed scaffolds was evaluated via live/dead cell assays.

Abstract The aging behavior of TEMPO-CNF suspensions is investigated using rheological measurements and experiments involving the free-falling solid sphere. The properties of CNF suspensions, which are formed of water and cellulose fibers with a large aspect ratio, are fundamentally different from those commonly known as model low-density gels. We characterize their aging utilizing SAOS rheometry following a period of shear rejuvenation, measuring the effect of aging time on the observed stress overshoot, and additionally measure the rheological hysteresis under continuous shear. In addition to such tests, which probe the sample at the bulk level, we study their local aging behavior via the Stokes’ experiment. During SAOS, the aging of the material results in a logarithmic growth of the elastic modulus over the first 50 minutes. In the Stokes’ experiment, depending on the sphere size, we find a systematic decrease in the sphere velocity with aging times up to 16 days and identify a range of intermittent particle motion. Based on our experimental evidence, we propose that the aging effect within the TEMPO-CNFs occurs due to the restructuring of fibrous elements by Brownian diffusion and that the aging of the system does not develop homogeneously across the whole sample as a consequence of the wide size distribution of CNFs. Finally, we note that this may be one of the primary reasons why the rheological data on even the same batch of CNFs show a large scatter. Graphical abstract

Crystal plasticity experiments consider fundamental physics of complex systems. With simulations, statistical analysis is performed on nanopillar compression. With the statistical data this thesis has done research for better understanding of the structure to yield stress relation. This thesis considers tantalum polycrystal nanopillar compression with two datasets. First of the two datasets considers 20 nm midway diameter Ta nanopillars with different grain sizes and indenter velocities. From the research done with the first dataset, there seems to be two regimes for the yield stress dependency on the grain size. For the average grain size larger than roughly 35 nm there seems to be a high dependency on the yield stress if the grain size is modified. If the grain size is increased, the yield stress increases, approaching the monocrystal yield stress. For grain sizes smaller than that, there seems to be almost no effect on the yield stress when it comes to modifying the grain size. With statistical analysis on another dataset, which considers 20 nm to 50 nm midway diameter Ta nanopillars, it is also proven that statistical analysis is necessary to draw reliable conclusions. This is proven by a fact that a similar study, with some differences, but still more than enough in common with this research, has different conclusions with single samples than with this study has with a statistical analysis.

Magneto-induced rheology control is beneficial to overcome the opposing property requirements in different construction processes. The viscoelastic properties of paste medium have great effects on the movement and distribution of magnetic particles when applying an external magnetic field and thus the degree of the rheological response. In the present research, the effect of (total) solid volume fraction ϕT on the magnetorheological (MR) response of nanoFe3O4 incorporated cementitious paste, represented by the early structural build-up is experimentally investigated. Cementitious pastes with various solid volume fractions are achieved by changing the water-to-cement ratio (w/c) of the paste medium while the nanoFe3O4 concentration remains unchanged. Results reveal that cementitious pastes with extremely low solid volume fractions acting as a dilute suspension show an insignificant increase in stiffness after applying an external magnetic field of 0.5 T, possibly due to the high surface to the surface separation distance between cement particles. Both the magnetic force between neighboring nanoparticles and the viscoelasticity of the suspension increase with increased solid volume fraction. At moderate solid volume fractions (e.g., 0.3

Shear thickening in stable dense colloidal suspensions is a reversible phenomenon and no hysteresis is observed in the flow curve measurements. However, a reduction in the stability of colloids promotes particle aggregation and introduces a time dependent rheological response. In this work, by using a model colloidal system of hard spherical silica particles (average diameter of 415 nm) with varying particle volume fractions 0.2 ≤ ϕ ≤ 0.56, we study the effect of particle stability on the hysteresis of the shear thickening behavior of these suspensions. The particle stability is manipulated by adding a simple monovalent salt (sodium chloride) in the silica suspension with varying concentrations α ∈ [0,0.5] M. For repulsive and weakly attractive suspensions, the flow behavior is history independent and the shear thickening behavior does not exhibit hysteresis. However, significant hysteresis is observed in rheological measurements for strongly attractive suspensions, with shear history playing a critical role due to the dynamic nature of particle clusters, resulting in time dependent hysteresis behavior. By performing numerical simulations, we find that this hysteresis behavior arises due to the competition among shear, electrostatic repulsive, van der Waals attractive, and frictional contact forces. The critical shear stress (i.e., the onset of shear thickening) decreases with increasing salt concentrations, which can be captured by a scaling relationship based on the force balance between particle–particle contact force and electrostatic repulsive force. Our combined experimental and simulation results imply the formation of particle contacts in our sheared suspensions.

Amorphous solids such as coffee foam, toothpaste or mayonnaise display a transient creep flow when a stress $\Sigma$ is suddenly imposed. The associated strain rate is commonly found to decay in time as $\dot{\gamma} \sim t^{-\nu}$, followed either by arrest or by a sudden fluidisation. Various empirical laws have been suggested for the creep exponent $\nu$ and fluidisation time $\tau_f$ in experimental and numerical studies. Here, we postulate that plastic flow is governed by the difference between $\Sigma$ and the transient yield stress $\Sigma_t(\gamma)$ that characterises the stability of configurations visited by the system at strain $\gamma$. Assuming the analyticity of $\Sigma_t(\gamma)$ allows us to predict $\nu$ and asymptotic behaviours of $\tau_f$ in terms of properties of stationary flows. We test successfully our predictions using elastoplastic models and published experimental results.

Processing, stability and sensorial perception of food foams are tightly related to their microstructure and flow behavior. Characterization of corresponding physical parameters is central for product development and quality control. An experimental setup enabling in-situ characterization of yield stress, gas volume fraction and bubble size distribution at different heights within a foam column created in a commercial whipping device is presented. Reliable determination of these quantities is shown. Foams made from regular and reconstituted milk have been investigated. Gas volume fraction and bubble size increase monotonically during free drainage. Related to the changes in these parameters, the yield stress increases strongly during initial drainage and weaker in mature foams. Gradients of the structural and rheological parameters along the direction of gravity increase over time. Yield stresses in these milk foams are as predicted from phenomenological modelling including the above parameters, emphasizing the reliability of the measurement setup.

Thixotropic structural build-up is an intrinsic property of fresh cementitious materials, playing a significant role in pumpability, stability and formwork filling of concrete, as well as buildability in 3D printing. This paper presents a critical review on the thixotropic structural build-up of cement-based materials from the viewpoints of origins, evaluation methods, influencing factors and applications. Recent research indicates that the origin of structural build-up of cementitious materials is a combining result of colloidal interactions and chemical hydration, with three stages of colloidal network percolation, rigid percolation and rigidification. The evolution of static yield stress and storage modulus can be used to evaluate the structural build-up of fresh cementitious materials, each describing different aspects. Increasing particle volume fraction, decreasing surface coverage and reducing maximum packing fraction exhibit a positive effect on the increase in the structural build-up. Based on the relationships with performance parameters, the thixotropic structural build-up can be used to predict formwork casting, numerical simulations and 3D concrete printing. Furthermore, on-demand stiffening can be obtained by magneto-controlled structural build-up of cementitious materials containing magnetizable particles.

This work deals with secondary instabilities in a Taylor-Couette flow with a wide gap in the case of shear-thinning fluids. Theoretical, experimental and numerical approaches are used. From theoretical point of view, a weakly nonlinear analysis has been done to account for the nonlinear effects of constitutive law on the flow structure of the Taylor Vortex Flow (TVF) regime. The shear-thinning behavior of the fluid are characterized by the Carreau model. Significant effects of shear-thinning have been demonstrated: Taylor vortices are smaller in size and shifted toward the inner cylinder. The radial outflow jet is thinner and stronger than the radial inflow jet. This asymmetry leads to an increase of the radial inflow zone. These changes in the flow structure are probably the origin of the secondary instabilities of Taylor vortices observed experimentally and numerically. The experimental setup consist of two coaxial cylinders where the inner cylinder is rotating and the outer one is at rest. The radius ratio is $eta = 0.4$ and the aspect ratio is $L = 32$. The fluids used are aqueous xanthan gum solutions at different concentrations and aqueous glycerol solution as a reference Newtonian fluid. The flow structure is analyzed through the visualization and by the 2D PIV velocity measurements. For the aqueous glycerol solution, once the primary bifurcation is reached at $Re = Re_c$, the stationary TVF regime remains stable up to practically $Re = 7 Re_c$. From this values the Taylor vortices lose its stability with respect to azimuthal disturbances. In the case of the aqueous xanthan gum solutions the values of the Reynolds number from which the Taylor vortices appear are in agreement with a linear theory as for the case of Newtonian fluid. By increasing the Reynolds number, the Taylor vortices become unstable, but with respect to axial disturbances. There instabilities can be considered as generalized Eckhaus instabilities. They are characterized by the continuous processes of creation and merging of vortices. The increase in the number of axial positions where these processes occur leads to the chaotic flow (phase turbulence). It should be noted that the stronger shear-thinning effects, the smaller the range of stable TVF regime. These results have been confirmed by a 2D numerical simulation of unsteady conservation equations, using PDE solver Freefem++. The case of shear-thinning with a stress-yield was started as well, focusing on the particular case when the unyielded zone is attached to the outer cylinder., On s’intéresse aux instabilités secondaires dans un écoulement de Taylor-Couette en grand entrefer pour un fluide rhéofluidifiant. Des études théorique, expérimentale et numérique ont été mises en œuvre. D’un point de vue théorique, une analyse faiblement non linéaire a été développée en régime dit TVF (Taylor Vortex Flow) pour rendre compte des premiers effets de la non linéarité de la loi de comportement sur la structure de l’écoulement. Le comportement rhéologique du fluide est décrit par le modèle de Carreau. Des effets significatifs du caractère rhéofluidifiant ont été mis en évidence : Les rouleaux de Taylor ont une taille plus petite et sont écrasés contre le cylindre intérieur. Le jet radial sortant est plus fin et beaucoup plus intense que le jet radial entrant. Par conservation de débit, la zone de jet radial entrant est plus étendue. Ces modifications sont probablement à l’origine des instabilités des rouleaux de Taylor observées expérimentalement et numériquement. Le dispositif expérimental utilisé est constitué de deux cylindres coaxiaux, où le cylindre intérieur est en rotation et le cylindre extérieur est fixe. Le rapport des rayons est $eta = 0.4$ et le rapport d’aspect $L = 32$. Les fluides utilisés sont des solutions de xanthane à différentes concentrations ainsi qu’une solution de glycérole, comme fluide newtonien de référence. La structure de l’écoulement est déterminée par visualisation et par mesures de vitesse par PIV 2D. Pour la solution de glycérole, après la bifurcation primaire à $Re = Re_c$, le régime TVF stationnaire reste stable jusqu’à pratiquement $7 Re_c$. A partir de cette dernière valeur, les rouleaux de Taylor perdent leur stabilité vis-à-vis de perturbations azimutales. Dans le cas des solutions de xanthane, les valeurs du nombre de Reynolds à partir desquelles, les rouleaux de Taylor apparaissent sont en accord avec la théorie linéaire comme dans le cas Newtonien. En augmentant le nombre de Reynolds, les rouleaux de Taylor deviennent instables, mais cette-fois-ci vis-à-vis de perturbations axiales. Ces instabilités peuvent être considérées comme des instabilités d’Eckhaus généralisées. Elles se caractérisent par un processus récurrent de création et d’appariement de rouleaux. L’augmentation du nombre de sites où se produit ce processus conduit à un écoulement chaotique (turbulence de phase). Il convient de noter que plus les effets rhéofluidifiants sont importants, et plus la gamme de Re où le régime TVF est stable, est réduite. Ces résultats ont été confirmés par une simulation numérique 2D des équations de conservation instationnaires, en utilisant le solveur de FreeFem++. Le cas des fluides rhéofluidifiants avec seuil de contrainte a été entamé , en se focalisant sur le cas particulier où il existe une zone non-cisaillée attachée au cylindre extérieur.

In this thesis, the solid/flowing transition in yield-stress fluids is investigated using laboratory experiments and numerical simulations. The results obtained from the fluid mechanics study are then applied to the dynamics of magmatic systems. The aims are to evaluate how the transition depends on the fluid structure and its elasticity, what ingredients are needed to describe mathematically this transition and fluid motion, and when this description will break down. Two systems have been chosen for the simplicity of their dynamics in Newtonian fluids and their relevance to geological systems: (1) the motion of a solid sphere, and (2) the development of thermal plumes. Case (1) regards the experimental work on the free-fall of a sphere through a mixture of water and superabsorbent gel grains. The aim here is to investigate the influence that the size of particles which build up the structure of the fluid has on the dynamics of a spherical intruder. Case (2) is instead approached through numerical simulations that combine viscoelasticity and viscoplasticity together. The role of elasticity on the overall deformation of the fluid is characterized. Results are afterwards applied to crustal magmatic reservoirs in which both small scale phenomena (such as the motion of bubbles and melt pockets) and larger scale phenomena (deformation on the top of an entire magmatic chamber) are examined.; Cette thèse étudie la transition solide/fluide dans les fluides à contrainte-seuil, en utilisant des expériences de laboratoire et des simulations numériques. Les résultats obtenus à partir de l’étude de mécanique des fluides sont ensuite appliqués à la dynamique des systèmes magmatiques. Les objectifs sont d’évaluer comment la transition dépend de la structure du fluide et de son élasticité, quels sont les ingrédients nécessaires pour décrire mathématiquement cette transition et le mouvement du fluide, et dans quelles conditions cette description n’est plus valide. Deux systèmes ont été choisis pour la simplicité de leur dynamique dans le cas Newtonien et leur pertinence pour les systèmes géologiques: (1) le mouvement d’une sphère solide, et (2) le développement des panaches thermiques. Dans le premier cas, on a caractérisé expérimentalement la chute libre d’une shère dans un mélange aqueux de gels superabsorbants. L’objectif est ici d’étudier l’influence de la taille des grains de gel qui constituent la structure du fluide sur la dynamique de l’intrusion sphérique. Dans le second cas, l’approche utilisée est numérique, avec des simulations combinant les effets viscoplastiques et viscoélastiques. Le rôle de l’élasticité sur la déformation du fluide est ainsi caractérisé. Les résultats sont ensuite appliqués aux réservoirs magmatiques dans la croûte terrestre, où sont examinés les phénomènes à petite échelle (le mouvement des bulles de gaz et des poches de liquide fondu dans la chambre magmatique) et à grande échelle (la remontée d’un diapir magmatique et la déformation de la croûte au dessus de la chambre magmatique).

In this thesis, the solid/flowing transition in yield-stress fluids is investigated using laboratory experiments and numerical simulations. The results obtained from the fluid mechanics study are then applied to the dynamics of magmatic systems. The aims are to evaluate how the transition depends on the fluid structure and its elasticity, what ingredients are needed to describe mathematically this transition and fluid motion, and when this description will break down. Two systems have been chosen for the simplicity of their dynamics in Newtonian fluids and their relevance to geological systems: (1) the motion of a solid sphere, and (2) the development of thermal plumes. Case (1) regards the experimental work on the free-fall of a sphere through a mixture of water and superabsorbent gel grains. The aim here is to investigate the influence that the size of particles which build up the structure of the fluid has on the dynamics of a spherical intruder. Case (2) is instead approached through numerical simulations that combine viscoelasticity and viscoplasticity together. The role of elasticity on the overall deformation of the fluid is characterized. Results are afterwards applied to crustal magmatic reservoirs in which both small scale phenomena (such as the motion of bubbles and melt pockets) and larger scale phenomena (deformation on the top of an entire magmatic chamber) are examined.; Cette thèse étudie la transition solide/fluide dans les fluides à contrainte-seuil, en utilisant des expériences de laboratoire et des simulations numériques. Les résultats obtenus à partir de l’étude de mécanique des fluides sont ensuite appliqués à la dynamique des systèmes magmatiques. Les objectifs sont d’évaluer comment la transition dépend de la structure du fluide et de son élasticité, quels sont les ingrédients nécessaires pour décrire mathématiquement cette transition et le mouvement du fluide, et dans quelles conditions cette description n’est plus valide. Deux systèmes ont été choisis pour la simplicité de leur dynamique dans le cas Newtonien et leur pertinence pour les systèmes géologiques: (1) le mouvement d’une sphère solide, et (2) le développement des panaches thermiques. Dans le premier cas, on a caractérisé expérimentalement la chute libre d’une shère dans un mélange aqueux de gels superabsorbants. L’objectif est ici d’étudier l’influence de la taille des grains de gel qui constituent la structure du fluide sur la dynamique de l’intrusion sphérique. Dans le second cas, l’approche utilisée est numérique, avec des simulations combinant les effets viscoplastiques et viscoélastiques. Le rôle de l’élasticité sur la déformation du fluide est ainsi caractérisé. Les résultats sont ensuite appliqués aux réservoirs magmatiques dans la croûte terrestre, où sont examinés les phénomènes à petite échelle (le mouvement des bulles de gaz et des poches de liquide fondu dans la chambre magmatique) et à grande échelle (la remontée d’un diapir magmatique et la déformation de la croûte au dessus de la chambre magmatique).

Nonlinear rheological properties are often relevant in understanding the response of a material to its intended environment. For example, many gastropods crawl on a thin layer of pedal mucus using a technique called adhesive locomotion, in which the gel structure is periodically ruptured and reformed. We present a mechanical model that captures the key features of this process and suggests that the most important properties for optimal inclined locomotion are a large, reversible yield stress, followed by a small shear viscosity and a short thixotropic restructuring time. We present detailed rheological measurements of native pedal mucus in both the linear and nonlinear viscoelastic regimes and compare this "rheological fingerprint" with corresponding observations of two bioinspired slime simulants, a polymer gel and a clay-based colloidal gel, that are selected on the basis of their macroscopic rheological similarities to gastropod mucin gels. Adhesive locomotion (of snails or mechanical crawlers) imposes a large-amplitude pulsatile simple shear flow onto the supporting complex fluid, motivating the characterization of nonlinear rheological properties with large amplitude oscillatory shear (LAOS). We represent our results in the form of Lissajous curves of oscillatory stress against time-varying strain. The native pedal mucus gel is found to exhibit a pronounced strain-stiffening response, which is not imitated by either simulant. ispartof: Soft matter vol:3 issue:5 pages:634-643 ispartof: location:England status: published

Rheology control is essential during the period in which cement and concrete pastes are encountered in the fresh state, due to the fact that it directly affects workability, initial placement and the structural performance of the hardened material. Optimizations of clinker formulations and reductions in cement-to-water ratios induced by economic and environmental considerations have a significant effect in rheology, which invokes the need for mechanistic models capable of describing the effect of multiple relevant phenomena on the observed paste flow. In this work, the population balance framework was implemented to develop a model able to relate the transient microstructural evolution of cement pastes under typical experimental conditions with its macroscopic rheological responses. Numerical details and performance are assessed and discussed. It was found that the model is capable of reproducing experimentally observed flow curves by using measured cluster size distribution information. It is also able to predict the complex rheological characteristics typically found in cement pastes. Furthermore, a spatially resolved scheme was proposed to investigate the nature of flow inside a parallel-plates rheometer geometry with the objective of assessing the ability of the model of qualitatively predicting experimentally observed behavior and to gain insight into the effect of possible secondary flows.

Magneto-rheology control, by means of adding magnetizable particles and applying magnetic field, is a potential approach to satisfy the contradicting requirements of fresh properties in different casting processes. Poly-carboxylate ether (PCE) superplasticizer is an essential component of modern cement-based materials, which significantly affects the viscoelastic properties of cementitious suspensions, and hence the movement and distribution of magnetic particles after applying an external magnetic field. This present research focuses on the following two aspects: whether highly flowable cementitious paste containing both magnetic particles and PCE shows rheological response to an external magnetic field, and if yes, is there a difference of magneto-responsive structural evolution of cementitious pastes with and without PCE? For these purposes, the magneto-responsive structural build-up of highly flowable cementitious pastes with various magnetic particles (two nano-Fe3O4 particles and one magnetic fly ash) in the presence of PCE, described by the evolution of storage modulus over time, is evaluated. Experimental results show that highly flowable cementitious pastes containing both magnetic particles and PCE indeed exhibit obvious magneto-rheological (MR) responses. The incorporation of PCE significantly increases the relative MR effect while slightly decreases the absolute MR effect. By comparing the magneto-responsive structural build-up of cementitious pastes with and without PCE, it is revealed that the application of an external magnetic field to a highly flowable cementitious paste with PCE mainly plays a significant role in the increase of solid-like properties.

© 2018, The Minerals, Metals & Materials Society and ASM International. The viscosity of solid phase containing heterogeneous silicate melts is discussed in this review. The crucial parameters characterizing silicate melt structure are first presented, i.e., volume fraction of solid particles, particle shape and size. The measurement and calculation methods of these parameters are summarized and the influence of the parameters on viscosity is discussed. Next, a theoretical description of rheological behavior in heterogeneous silicate melts is given, focusing on non-Newtonian characteristics, e.g., shear-dependence, time-dependence, and yield stress. The viscosity models which were proposed in the last half century are reviewed and critically assessed. This paper concludes with opportunities and suggestions for future work. ispartof: METALLURGICAL AND MATERIALS TRANSACTIONS B-PROCESS METALLURGY AND MATERIALS PROCESSING SCIENCE vol:49 issue:5 pages:2469-2486 status: published

The refining characteristics of the highly concentrated water-in-oil emulsion, which are used as ‘emulsion precursors’ for the preparation of emulsion explosives, were investigated to elucidate the manner in which the refining time influences its microstructure and rheological behaviour. The development of microstructure at various stages of the emulsification process has been studied in detail and an empirical correlation between the characteristic droplet size and refining time has been proposed. The evolution of rheological characteristics of the emulsion during the microstructure refinement has been investigated through different protocols of the dynamic and steady-state rheology. An extended refining led to a finer microstructure and resulted in an increase in the elastic modulus, yield stress and viscosity of the emulsion. The droplet size dependency of the elasticity and the yield stress during the refining have also been discussed. The network structure of the dispersed phase, the droplet size and the corresponding interdroplet interactions all govern the rheological characteristics of the final emulsion.

WOS:000395847500002; International audience; Rheometers with specific impellers, developed to characterize the behavior of cement-based suspensions in the fresh state, are used to limit the heterogeneities induced during shearing but they make the identification of the rheological parameters less straightforward compared to conventional rheometers. This paper presents the inverse analysis method and discusses the quality of this identification procedure when applied to such materials. The procedure includes a CFD simulation based on the finite element method using a Herschel-Bulkley model. Two kinds of optimization algorithms are used: a deterministic simplex method and a stochastic genetic method. As a first step of a larger study, the procedure reported in this paper used 2D synthetic data, i.e. 2D numerically generated experimental data. Two numerical vis-coplastic materials, characterized by shear-thinning and shear-thickening, were selected and studied. The results obtained with the two algorithms are systematically compared to the known parameter solution. Three approaches corresponding to three levels of user's knowledge about the material under study are considered successively: (1) the user has no a priori knowledge about the material, (2) the user knows whether the material is shear-thinning or shear-thickening and (3) the user is able to estimate the behavior index. The time-consuming genetic method appears to be suitable when the a priori knowledge of the material is slight, whereas the simplex method gives a reliable solution in a few iterations when the level of knowledge is higher. Both algorithms encounter more difficulties with the shear-thinning material than with the shear-thickening one. In this paper, the advantage provided by the genetic method regarding the non-uniqueness of the identification procedure for real experimental data is also highlighted: this method provides a collection of satisfactory solutions among which the user can select the optimal one based on his scientific background and/or on further experimental test results.

The determination of rheological and mechanical material properties becomes a challenge when the availability of material is limited to a few (milli)grams. This miniaturized testing is hampered by the contradicting requirements of small sample sizes (and thus surface areas) and sufficiently large generated torques and forces. In this paper we provide a feasible methodology to determine the relevant material parameters in terms of processing and mechanical performance starting from 30 mg of material, using micropillars with a diameter of 1 mm. Complex viscosity in small amplitude oscillatory shear as the relevant parameter for thermoconformation processes is determined by means of eccentric rheometry. Herein, the sample is placed off-centered, which results in an increase in the generated torque without the need for increasing the size of the sample. By combining experimental data and numerical simulations, we show that the choice of the pillar aspect ratio is essential to maintain a homogeneous sample deformation and thus to extract correct rheological parameters. Values obtained with eccentric rheometry collapse with those obtained from standard rheometry. The intrinsic mechanical behavior is evaluated at room temperature and the yielding kinetics is studied. The methodology developed here can be extended to other systems and testing conditions, allowing a full material characterization in the liquid as well as in the solid state with only 30 mg of material.

Predicting the dramatic changes in mechanical and physical properties caused by irradiation damage is key for the design of future nuclear fission and fusion reactors. Self-ion irradiation provides an attractive tool for mimicking the effects of neutron irradiation. However, the damaged layer of self-ion implanted samples is only a few microns thick, making it difficult to estimate macroscopic properties. Here we address this challenge using a combination of experimental and modelling techniques. We concentrate on self-ion-implanted tungsten, the frontrunner for fusion reactor armour components and a prototypical bcc material. To capture dose-dependent evolution of properties, we experimentally characterise samples with damage levels from 0.01 to 1 dpa. Spherical nano-indentation of grains shows hardness increasing up to a dose of 0.032 dpa, beyond which it saturates. Atomic force microscopy (AFM) measurements show pile-up increasing up to the same dose, beyond which large pile-up and slip-steps are seen. Based on these observations we develop a simple crystal plasticity finite element (CPFE) model for the irradiated material. It captures irradiation-induced hardening followed by strain-softening through the interaction of irradiation-induced-defects and gliding dislocations. The shear resistance of irradiation-induced-defects is physically-based, estimated from transmission electron microscopy (TEM) observations of similarly irradiated samples. Nano-indentation of pristine tungsten and implanted tungsten of doses 0.01, 0.1, 0.32 and 1 dpa is simulated. Only two model parameters are fitted to the experimental results of the 0.01 dpa sample and are kept unchanged for all other doses. The peak indentation load, indent surface profiles and damage saturation predicted by the CPFE model closely match our experimental observations. Predicted lattice distortions and dislocation distributions around indents agree well with corresponding measurements from high-resolution electron backscatter diffraction (HR-EBSD). Finally, the CPFE model is used to predict the macroscopic stress-strain response of similarly irradiated bulk tungsten material. This macroscopic information is the key input required for design of fusion armour components.

Robustness is defined as the capacity of cement-based materials to retain fresh properties when subjected to either small variations in the constituent elements or small changes in the mixing procedure. Compared to normal concrete, self-consolidating concrete (SCC) may show less tolerance to those changes. Most robustness studies focus on initial rheological properties or workability, but concentrate less on the evolution of these properties within the first hour(s). This paper presents the results of an investigation aimed at evaluating the change of yield stress and plastic viscosity with time of cement pastes with SCC consistency, which is mainly affected by variations in the water content and the adding time of the superplasticizer. A change in water content also influences the initial rheological properties, and these differences are amplified over time. The difference due to the different adding time of the superplasticizer is, however, reduced or even reversed over time.

The aim of this study was to use a detailed rheological characterization to gain new insights into the gelation behavior of natural waxes. To make a comprehensive case, six natural waxes (differing in the relative proportion of chemical components: hydrocarbons, fatty alcohols, fatty acids, and wax esters) were selected as organogelators to gel high-oleic sunflower oil. Flow and dynamic rheological properties of organogels prepared at critical gelling concentrations (Cg) of waxes were studied and compared using drag (stress ramp and steady flow) and oscillatory shear (stress and frequency sweeps) tests. Although, none of the organogels satisfied the rheological definition of a "strong gel" (G″/G' (ω) ≤ 0.1), on comparing the samples, the strongest gel (highest critical stress and dynamic, apparent, and static yield stresses) was obtained not with wax containing the highest proportion of wax esters alone (sunflower wax, SFW) but with wax containing wax esters along with a higher proportion of fatty alcohols (carnauba wax, CRW) although at a comparatively higher Cg (4%wt for latter compared to 0.5%wt for former). As expected, gel formation by waxes containing a high proportion of lower melting fatty acids (berry, BW, and fruit wax, FW) required a comparatively higher Cg (6 and 7%wt, respectively), and in addition, these gels showed the lowest values for plateau elastic modulus (G'LVR) and a prominent crossover point at higher frequency. The gelation temperatures (TG'=G″) for all the studied gels were lower than room temperature, except for SFW and CRW. The yielding-type behavior of gels was evident, with most gels showing strong shear sensitivity and a weak thixotropic recovery. The rheological behavior was combined with the results of thermal analysis and microstructure studies (optical, polarized, and cryo-scanning electron microscopy) to explain the gelation properties of these waxes.

Soft and semisolid states of fine-grained soils and clay minerals (FGS-CMs) are frequently dealt with during execution of infrastructure projects located in the coastal areas, analysis of natural hazards, and mineral processing. In most of these cases, the FGS-CMs flow like a slurry, and hence determination of their rheological characteristics becomes essential. However, test methods and approaches available for determining the rheological behavior of the FGS-CMs when they transform from the solid to the liquid state are yet to evolve. This study uses a parallel-plate rheometer, which is widely used for rheological characterization of complex fluids (i.e., fluids which exhibit yield stress), to determine the rheological parameters (i.e.,yield stress, T-y, and strains) of the FGS-CMs with a consistency near the liquid limit. A critical analysis of the existing protocols that are used to determine T-y and their applicability to FGS-CMs is conducted. The constant shear-rate (CSR) test, when conducted at low shear-rate, yields the most accurate T-y of FGS-CMs. Subsequently, the results are used to develop a generalized relationship which explains the variation of the T-y of the FGS-CM with the consistency represented as water content normalized with respect to the liquid limit. Furthermore, to understand the nature of strains that develop during the preyielding regime of FGS-CMs, creep-relaxation (CR) tests are conducted by imposing stress equivalent to different fractions of T-y. The results from CR tests were utilized in the development of a novel methodology to determine the elastic component of the shear modulus, G(E), of FGS-CMs. This study reveals that FGS-CMs behave as a linear elastoplastic material in the preyield stage, contrary to the much expected purely elastic response, providing a new insight in the realm of contemporary geomechanics. (C) 2018 American Society of Civil Engineers.

A natural emulsion was used to create a high internal phase emulsion (HIPE) gel with elastic properties, indicated by shear elastic moduli between 102 and 105 Pa. The elasticity of the gel network was provided from a 2D-gel network of proteins which were naturally adsorbed at the interface of an oil-in-water emulsion formed after aqueous extraction of oil bodies from sunflower seeds. Extensive centrifugation of the obtained emulsion resulted in a stable ultrahighly concentrated emulsion with an oil volume fraction of 0.91 and a protein content of 2.5 wt% only. This high volume fraction of the emulsion cream was achieved due to the large deformability (low rigidity) of the oil body surface. After formation of the HIPE, the rigidity of the interfacial network was increased by addition of small concentrations of Ca2+ and heating at 72 °C for 10 min. This led to aggregation of the interfacial proteins, thereby forming a 2D interfacial gel providing a space-spanning network. The behaviour of the self-supporting gel exhibited increased elastic behaviour, determined by the increased elastic modulus of the interfacial network. The balance between the low rigidity upon formation and the increased rigidity after formation offers a tempting strategy to produce structured solid matter that contains edible hydrophobic liquids. Additionally, the followed procedure is cost-effective and friendly to the environment.

The rheological properties of high internal phase emulsions (HIPEs), comprising polydisperse aqueous droplets in oil, have been characterized as a function of emulsification time, salt concentration, phase mass fractions and aging. The droplet size distribution and structural details of the emulsion samples were obtained using cryogenic-scanning electron microscopy (cryo-SEM) and optical microscopy. For rheological characterisation, amplitude sweep tests performed on HIPE samples with a high mass fraction of dispersed phase (93.5 wt%) show that the strain behavior, especially the yield strain ( e y ) and crossover strain ( e c ), are almost independent of the droplet size and polydispersity. However, emulsions with smaller droplets have higher yield stress ( τ y ) and storage moduli ( G ′ ) values; explanations for these observations, based on the physical properties of the systems are suggested. Furthermore, it is observed that, for constant mass fractions of oil and aqueous phases, the strain behavior is also independent of the salt concentration in the dispersed phase. Our findings indicate that, independently of the salt concentration, the energy requirement for the emulsion to start flowing is greater when smaller droplets are present. Aging studies, performed over a period of 6 months, show no significant change in the rheological properties of the HIPEs. Experimental rheology data is compared to the Princen and Kiss model, and with modified Mougel model (Ind. Eng. Chem. Res. 2011, 50, 10359–10365), giving insight into the critical effects of non-ideality induced by polydispersity in thickened emulsions.

The response of a two-dimensional liquid foam to a localized air injection is investigated experimentally and theoretically. The experiments show a rich phenomenology, with two essentially distinct behaviours, depending on the injection conditions. At low flux, the injected air forms a central bubble that grows inside the foam and induces plastic rearrangements, without film rupture. This ‘pure swelling’ regime is reminiscent of ductile fracture. In this regime, the central bubble shows fingering patterns beyond a certain velocity. The dependence among the swelling rate, the injection overpressure and the other control parameters, namely cell gap, bubble size and foam area, is captured by a simple balance between the pressure drop and bubble/wall friction under a radial assumption. Fingering is successfully modelled by the linear stability analysis of an azimuthal perturbation of the radial model; yield stress becomes an important parameter to determine the finger width. At high injection rate, films are broken and narrow cracks form rapidly through the foam, reminiscent of brittle fracture. Criteria for the transition between ductile and brittle behaviours are investigated, both at the local and global scales.

Repeated stress-relaxation experiments are conducted from RT to 1073 K on three different gamma + alpha(2) TiAl alloys (Ti-46Al with 8Ta, 8Nb or 7Nb) One is a conventional duplex alloy, the two other are novel "convoluted" cast titanium aluminides developed for turbine applications The data include measurements of the flow stress and activation volume of these alloys at 293, 673, 873, 923, 1023 and 1073 K. Despite differences in composition, processing and microstructure, the values and evolution with temperature or with stress of these parameters are relatively similar for the three alloys This observation, coupled with the agreement of present results with data in the literature for similar alloys, leads to conclude that the strain-rate dependence of plastic flow in alloys of this class is governed by features of the gamma-phase that are relatively insensitive to the alpha 2 phase morphology. The convoluted alloys furthermore feature a yield stress anomaly. (C) 2010 Elsevier Ltd All rights reserved.

A working model for engineering analysis of pressure filtration is presented. Based on the filtration characteristics of fine and colloidal suspensions, the process was divided into two stages. A time-invariant spatially uniform volume fraction of solids approximation is invoked in the growing filter cake stage (stage 1). A time-dependent spatially uniform volume fraction of solids assumption is made in the cake consolidation stage (stage 2). The two models, named collectively as Mean Phi (M-P) model, have a common physical basis, seamless continuity between the stages and internal consistency. The M-P model has only three parameters: terminal or equilibrium volume fraction of solids in the filter cake that is related to its compressive yield stress, critical volume fraction of solids, which joins stage 1 and stage 2, and a permeability factor, which is common to stages 1 and 2. The model is validated with a large number of colloidal suspensions filtered under highly diverse physical-chemical process conditions. A Pareto profile is identified that relates the timescale of filtration and the extent of dewatering achieved, the two most important performance indices of the process.

The correlation between the Bostwick degree and the static rheological properties of yield stress food fuids is first revisited and then reformulated in this work. The role of the yield stress in the free surface flow of the Bost-wick test is studied using dimensional analysis. Results from experiments on 48 different samples of yield stress fluids are considered and included to check the adequacy of the proposed correlation. Asymptotic dynamic behaviour is also presented and discussed as a mechanism of complete self similarity with respect of the dimensionless time. This approach would seem to support the opinions in favor of the yield stress as a key parameter, and thus offers an interesting new viewpoint useful to both future experiments on the Bostwick test and studies of 'dam-break' like dynamics.

We review recent developments in the field of microrheometry and describe a new flexure-based microrheometer (FMR) that can make measurements of the steady shear viscosity of transparent oroptically-opaque complex fluids using 1-10 mul samples. We document the complex microrheology that may arise in a typical consumer product such as a skin creme, when the microstructure of the multiphase material (in this case a oil-water emulsion containing microcrystalline wax particles) and the characteristic length scale of the flow device become comparable. The material is a highly filled emulsion and conventional cone-and-plate rheometry shows that the material exhibits an apparent yield stress. Analogous tests in the microrheometer show that a sequence of flow transitions occurs which lead to an apparent viscosity that is both gap and shear-stress- (or shear-rate)-dependent. The microrheological measurements are combined with a slip analysis and optical microscopy to formulate a 'phase diagram' identifying the critical stress and corresponding slip velocity for each flow transition as a function of the gap. In the case of the skin creme investigated in the present study, the flow behavior in small gaps below 100 mum is dominated by the presence of micro-crystalline wax particles with mean diameters in the range of 50 mum. The sudden decrease in the apparent viscosity, or equivalently the sudden increase in the slip velocity between two surfaces with decreasing gap and increasing applied stress, is of importance in end-user perceptions of textural quantities such as 'slipperiness' or 'lubricity' which are typically used to characterize creams and other complex consumer products. The ability to progressively vary the gap between the two shearing surfaces means that the flexure-based microrheometer developed in the present work may find future applications in helping to bridge the gap between the traditionally-distinct fields of bulk rheological characterization and tribological testing. (C) 2004 Elsevier B.V. All rights reserved. ispartof: Journal of non-newtonian fluid mechanics vol:124 issue:1 pages:1-10 ispartof: location:WALES, Cardiff status: published

WOS:000347493700077; International audience; This paper is part of a study aiming to define the best way to incorporate recycled concrete aggregates (RCA) in the production of self-compacting concrete (SCC), with a view to reduce the excessive use of natural aggregates, which are a non-renewable resource, and to remove the large quantities of concrete waste generated by demolition. RCA differ from natural aggregates essentially by their lower density, higher water absorption capacity and systematic angularity. Here, the effect on self-compacting ability of replacing natural coarse aggregates (NCA) with coarse RCA in a dry state at the time of mixing is assessed. Starting from a reference SCC incorporating rounded NCA only, three replacement rates were studied: 40%, 60% and 100% by weight. The water amount was adjusted so that the standardized 24-h absorption of RCA was satisfied. The key properties of SCC recommended by European specifications and guidelines (EFNARC), i.e. filling ability, passing ability and segregation resistance, were measured in the fresh state, immediately after mixing (t(0)). Shear-dependent properties were also quantified by means of rheological measurements at t(0) and t(0) + 25 min. Through this study are shown and interpreted the difficulties in achieving the self-compacting ability under certain conditions of use of RCA. The experimental results showed that the self-compacting ability criteria were not satisfied, irrespective of the replacement rate of NCA with RCA. This replacement implied an increase in the rheological properties (yield torque and torque in steady-state flow) of concrete. The increased volume of coarse aggregates together with a constant volume of interstitial paste, and the angular shape and rough surface texture of RCA, are the main causes of the alteration of the flow of concrete. Also, the impairment with time of the flow properties of concrete was noted and is due to the movement of water from the interstitial paste towards dry RCA. Such results were supported by the fact that rheological data on RCA concretes were not in agreement with multi-scale models describing the flow of reference concrete as a suspension of spherical occlusions in a viscoplastic phase. Through this study, it is evidenced what to avoid regarding the technical approach envisaged to the RCA incorporation in SCC. (C) 2014 Elsevier Ltd. All rights reserved.

A method based on Tikhonov regularization is used to process the volumetric flow rate against pressure drop data of different fruit purees generated by large-scale flow loops. These data are converted into shear-rate-against-shear-stress curves. Curves from flow loops with different dia are compared to verify that they are independent of dia. They are also compared against that obtained by a conventional method. Tikhonov regularization will simultaneously extract the yield stress of the purees from the flow loop data. The results obtained by Tikhonov regularization show it to be a very efficient way of processing the flow loop data of rheologically complex foods.

In this paper we investigate the yield condition in the mobilization of yield-stress materials in distensible tubes. We discuss the two possibilities for modeling the yield-stress materials prior to yield: solid-like materials and highly-viscous fluids and identify the logical consequences of these two approaches on the yield condition. As part of this investigation we derive an analytical expression for the pressure field inside a distensible tube with a Newtonian flow using a one-dimensional Navier-Stokes flow model in conjunction with a pressure-area constitutive relation based on elastic tube wall characteristics., 28 pages, 1 figure

Plumes are known to migrate through the ductile quasi-Newtonian mantle, while dikes fracture and propagate through the solid lithosphere. However, depending on the timescale, the lithosphere presents solid as well as viscous properties. To determine what happens in the complex case, where instabilities propagate through a visco-elastic matrix, we performed a combined study of laboratory experiments and numerical simulations. Here we investigate the development of thermal plumes in aqueous solutions of Carbopol, a polymer gel, forming a continuous network of micrometric sponges. This fluid is shear thinning and has a yield-stress σ₀, whereby flow occurs only if the local stress exceeds this critical value σ₀. Below this value, the fluid acts as an elastic solid. The rheological properties of the solutions can be systematically varied by varying the Carbopol concentration. The setup consists of a localized heat-source operated at constant power, placed at the centre of a square tank. Depending on the ratio of the thermally induced stresses and the yield stress, Y₀, three different regimes may be obtained. For low Y₀Yc₂. We show that the critical parameters (Yc₁,Yc₂) strongly depend on the geometry of the heating. Combined temperature and velocity field measurements show that the morphology of the plume resembles a finger, contrary to the mushroom-like shape encountered in Newtonian fluids. Numerical simulations using a purely viscous description, where the rheology of the fluid is described by a regularized Herschel-Bulkley model, are sufficient to capture the plume dynamics. A detailed parametric study shows that the plume dynamics are governed by the interplay between yield stress, buoyancy induced stress and viscous stresses. We identify two non-dimensional parameters: the yield parameter Ψ comparing the buoyancy induced stress to the yield stress, and the Bingham number Bi comparing the yield stress to the viscous stresses. We show that a plume can rise only if both parameters are supercritical, i.e. if buoyancy induced stress and viscous stresses each overcome the yield stress. Therefore the plume may come to a halt before it reaches the surface. We propose scaling laws for the plume stem velocity, temperature and the size of the shear zone in the steady state. We show that the scaling laws describe the behaviour in the plume stem reasonably well, if the yield stress is neglected and only the shear thinning behaviour is taken into account. Applying the non-dimensional parameters to Earth places severe constraints on the strength of mantle and lithosphere. The maximum strength that allows for thermal instabilities to penetrate the lithosphere or upper mantle is in between 100 kPa and 100 MPa, and strongly depends on the size and buoyancy of the anomaly., Des panaches sont connus pour migrer à travers le manteau ductile et quasi-Newtonien ; alors que les dikes se fracturent et se propagent dans la lithosphère solide. Cependant, la lithosphère est en fait visco-élastique. Afin de déterminer ce qui se passe dans ce cas complexe, nous avons réalisé une étude expérimentale et numérique sur le développement de panaches thermiques dans des solutions aqueuses de Carbopol, un gel de polymères formant un réseau continu d'éponges microscopiques. Ce fluide est rhéofluidifiant et présente un seuil de contrainte σ₀, de sorte que l'écoulement ne se produit que si la contrainte locale dépasse cette valeur critique σ₀. En dessous de cette valeur, le fluide agit comme un solide élastique. Les propriétés rhéologiques des solutions peuvent être systématiquement ajustées en variant la concentration de Carbopol. Le dispositif consiste en une source locale de chaleur de puissance constante placée au centre d'une cuve cubique. Selon la valeur du rapport entre la contrainte d'origine thermique et la contrainte seuil, Y₀, on peut observer trois régimes différents. A faible Y₀Yc₂. Nous montrons que les paramètres critiques (Yc₁,Yc₂) dépendent fortement de la géométrie du chauffage. Des mesures simultanées de température et de champs de vitesse montrent que la morphologie du panache ressemble à un doigt, contrairement à la forme de champignon rencontrée dans les fluides newtoniens. Utilisant des simulations numériques avec une description purement visqueuse, où la rhéologie du fluide est décrite par un modèle de Herschel-Bulkley régularisé, sont suffisantes pour rendre compte de la dynamique du panache. Une étude détaillée des paramètres indiquent que la dynamique du panache est gouvernée par la compétition entre la contrainte seuil, la contrainte induite par la flottabilité et les contraintes visqueuses. Nous avons identifié deux paramètres adimensionnés : le paramètre seuil Ψ comparant la contrainte induite par la flottabilité et la contrainte seuil, et le nombre de Bingham Bi comparant la contrainte seuil et les contraintes visqueuses. Un panache ne peut s'élever que si les deux paramètres sont supercritiques, i.e. la contrainte induite par la flottabilité et les contraintes visqueuses sont plus importantes que la contrainte seuil. Par conséquent, le panache peut s'arrêter avant d'atteindre la surface. Des lois d'échelles dans le conduit du panache ont été déterminées pour la vitesse, la température et la taille de la région cisaillée en régime permanent. Elles décrivent raisonnablement le comportement du conduit bien que seul l'effet rhéofluidifiant soit pris en compte. L'application de ces paramètres adimensionnés à la Terre contraignent significativement la limite de plasticité du manteau et de la lithosphère. La contrainte seuil maximale qui permet à une instabilité thermique de pénétrer dans la lithosphère ou le manteau supérieur est entre 100 kPa et 100 MPa, et elle dépend fortement de la taille et de l'anomalie de densité de l'intrusion.

International audience; An approach based on percolation theory is associated to the rigorousness of the two-dimensional (2D) model of close-packed, monodisperse, cylindrical emulsions established by Princen, to obtain an equation to model the dispersed-phase volume fraction (phi) dependence of the storage modulus (G') of highly concentrated emulsions. A first-order Taylor expansion of this general percolation model leads to an expression similar to the three-dimensional (3D) model proposed by Princen and Kiss for real polydisperse emulsions, with a more satisfactory derivation of the function E(phi). Finally, the robustness of this model is tested against different experimental data collected from the literature.