Transient Rheological Behavior Research Articles

Coupling slip and thixotropy to model the transient rheological behaviour of kaolinite suspensions

Coupling slip and thixotropy to model the transient rheological behaviour of kaolinite suspensions

A pressure-sensitive rheological origin of high friction angles of granular matter observed in NASA–MGM project

Abstract An abnormally high peak friction angle of Ottawa sand was observed in (National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.

Steady and transient rheological properties of four polysaccharides with different chain conformations

AbstractCarbohydrate polymers have broad application prospects, especially in food and cosmetic fields, and rheology is very important for controlling the quality and functions of their final products. Therefore, the steady and transient rheological behaviors of polysaccharides with different chain conformations of triple helix, double helix, and random coils were studied systematically. In our findings, the extraordinary low‐shear thickening phenomena of polysaccharides (lentinan, curdlan, and xanthan) with helix conformation were observed at a certain concentration depending on the stiffness and molecular weight, different from the steady‐shear rheological property of pullulan, which was attributable to the arrangement from order to disorder of stiff chains at the shear rate of < 0.1 s−1. Lentinan, curdlan, and xanthan in solution showed obvious viscoelasticity and thixotropic behavior with significant concentration and stiffness dependence, while the flexible pullulan only exhibited Newtonian viscous fluid even at high concentration of 20%. Stress overshoot for the four polysaccharides occurred after shearing, and the higher stiffness and molecular weight delayed the occurrence of stress overshoot. Obviously, chain conformation plays a key role on controlling the rheology of polysaccharides. This work provides scientific basis for the application of these polysaccharides in food and cosmetics field.

Characterization of transient rheological behavior of soft materials using ferrofluid droplets

Physical material properties, such as elasticity, viscosity, or viscoelasticity, can be characterized by using rheometers or stick-type solenoid electromagnets. In this work, we developed a magnet measurement setup based on a Helmholtz arrangement of electromagnets. While applying homogeneous magnet fields to ferrofluid droplets inside a soft material of interest, the deformations of the ellipsoidal deformed droplets were measured. Kelvin-Voigt models and corresponding analytical descriptions were used to calculate the values of viscosity and Young’s modulus of materials under test. For calibration purposes of the developed setup, glycerin/water mixtures and methylcellulose/water solutions were characterized as viscous and polyacrylamide gels as elastic materials, respectively. In addition, the interfacial tensions were calculated with respect to the magnetic Bond number from the droplet deformations. For the first time, the transient rheological behavior of viscoelastic material was measured using the method of ferrofluid droplet deformation. When polyacrylamide gel with a shear modulus of 230 Pa was evacuated for less than 40 min during preparation, it showed a strong time-depending viscoelastic behavior several minutes after starting the measurements. Here, Young’s modulus increased up to the value of elastic behavior, whereas the values for viscosity decreased to a baseline. The developed setup can favorably be used in future applications to investigate local and also time-dependent rheological properties of soft materials.

On the co-evolution of dislocations and grains in deforming rocks

Deformation at tectonic plate boundaries is governed by the mechanical properties of crustal and lithospheric rocks, which evolve through changes in the microstructure of their constituent minerals. Geological observations of microstructure can, therefore, provide estimates of the rock's deformation conditions through various piezometers (e.g., the relationship between stress and grain size or dislocation density). However, grain size and dislocation density do not evolve independently, and thus their associated piezometers are unlikely to be decoupled. We present a new theoretical model coupling the evolution of grain boundaries and dislocations in a deforming rock and make a novel prediction that the equilibrium dislocation density at a given stress (the dislocation piezometer) can be non-unique, with co-existing deformation states or piezometric branches. One stable piezometric branch exists at high stress and large grain-size, for which the steady state dislocation density is large and dictated by stress, in agreement with experimental observations and earlier theoretical models. However, another stable branch exists at low stress and small grain-size, in which case dislocation density is small, weakly stress-dependent, and is governed by the balance between dislocation sinks and sources at grain boundaries. The contrast in dislocation density between grains of different sizes induces grain boundary migration from smaller grains into larger grains. Dislocation-induced grain boundary forces thus act in the opposite direction to those dictated by surface energy, for which grain boundaries migrate from larger grains into smaller ones. When forces due to surface and dislocation energies are balanced, the system reaches a stable microstructural equilibrium, thereby halting grain growth and helping preserve plate boundary weakness. When the forces are not in balance, unstable and oscillatory behavior can ensue, with oscillation periods on the order of decades. Finally, the new theory provides a microphysical model for transient rheological behavior, which is particularly relevant to tectonic activity in which deformation is relatively rapid and where the steady state flow laws are a poor approximation, such as during postseismic relaxation or postglacial rebound.

Characterization of Transient Rheological Behavior of Soft Materials Using Ferrofluid Droplets

Characterization of Transient Rheological Behavior of Soft Materials Using Ferrofluid Droplets

Frequency Dependent Mantle Viscoelasticity via the Complex Viscosity: Cases From Antarctica

AbstractStudies of glacial isostatic adjustment (GIA) often use paleoshorelines and present‐day deformation to constrain the viscosity of the mantle and the thickness of the elastic lithosphere. However, several studies focused on similar locations have resulted in different estimates of these physical properties. We argue that these different estimates infer apparent viscosities and apparent lithospheric elastic thicknesses, dependent on the timescale of deformation. We use recently derived relationships between these frequency dependent apparent quantities and the underlying thermodynamic conditions to produce predictions of viscoelastic properties and lithospheric thickness across a broad spectrum of geophysical timescales for two Antarctic locations (Amundsen Sea Embayment and the Antarctic Peninsula). Our predictions are constrained by input from seismic tomography, require the self‐consistent consideration of elastic, viscous, and transient rheological behavior and also include non‐linear steady state viscosity, which have been determined by several laboratories. We demonstrate that when the full spectrum of viscoelasticity is considered, lithospheric thickness displays a significant range across frequency and that transient creep may play an important role across the timescales relevant for the GIA studies we explore. We suggest that observational studies could move toward a framework of determining the frequency dependence of viscoelastic quantities—rather than single, frequency independent values of viscosity. There remains much work to accomplish this both theoretically and observationally, but the eventual result would provide deeper insight into the rheological behavior of Earth.

A Constitutive Model Describing Molecular Configuration Evolution and Transient Rheological Behavior of Entangled Polymer Solutions

The entanglement network is an important structural feature in polymer 10 concentrated solutions and melts, which has a great influence on the transient 11 rheological behavior and molecular configuration evolution. However, the existing 12 constitutive models have limitations in describing the influence of dynamic 13 entanglement behavior on molecular chain motion, resulting in inaccurate descriptions 14 of the transient rheological behavior. Thus, a molecular configuration evolution model 15 for polymer solutions considering the dynamic entanglement effect is proposed by 16 introducing an intermolecular force that changes with the orientation of the molecular 17 chain in this work. The intermolecular force is introduced by considering the friction 18 coefficient as anisotropic, and the orientation effect is considered by introducing an 19 excluded volume dependent anisotropic diffusion. The proposed model can better 20 describe the stress relaxation, stress growth, and dielectric anisotropy of polymer 21 solutions compared with the anisotropy FENE model and FENE model, which means 22 the proposed model can better describe the transient rheological behavior and 23 configuration evolution of polymer solutions. In addition, the influence of different 24 model parameters on the transient and steady shear response of polymer solution is 25 investigated, and the results show that the influence of volume loss on the friction 26 anisotropy factor kσ increases as the solution concentration increases.

Transient interfacial rheology and polar component dynamics at oil-brine interfaces

Interfacial deformation processes have diverse impacts on numerous industrial applications, including the petroleum industry. This study aimed to investigate the interfacial rheology and polar component dynamics in crude oil and brine systems using a wide range of salinity. The oscillating pendant-drop technique was utilized to evaluate the transient and equilibrium oil-brine interfacial rheological behavior and the associated diffusion, adsorption, and rearrangement processes of the bulk-dispersed and interfacially adsorbed polar components. A new logistic equation is proposed to model the transitory rheology of oil-brine interfaces, enabling the quantitative comparison of their behaviors. The conducted modeling approach indicated that the diffusion/adsorption processes are the dominant relaxation mechanisms over reorientation/rearrangement processes (negligible) when the interfaces are perturbed at different aging times. Furthermore, the results show that (a) the rate at which apparent interfacial elasticity increases is frequency-independent, (b) there are two local maximums for apparent interfacial viscoelasticity with brine salinity variation, (c) polar component dynamics in the studied crude oil are mainly controlled by diffusion, and (d) absence of significant lateral interactions of adsorbed species on the interface. Transient interfacial rheology is demonstrated to be of great importance when defining final apparent interfacial properties, and the potential consequences of these new findings on enhanced oil recovery applications are discussed.

Mesoscopic rheological modeling of drilling fluids: Effects of the electrolyte

Drilling fluid is a complex fluid, including base fluid and other materials, carrying out the vital functions during drilling operation such as cutting transport and controlling formation pressure. In order to optimize performance of a drilling process, a reliable rheological model is required in the computation of fluid flow dynamics. Time-independent Generalized Newtonian formulation are the most common models for describing the rheological behavior of drilling fluids due to its simplicity and ease of use, in spite the fact that they are not able to predict the normal stresses and could not consider effects of active components on the rheological behavior of the drilling fluid and also could not describe the internal microstructures changes in the fluid during its flow. In this paper, a rather simple model in the mesoscopic level of study through the Generalized Bracket formalism have been developed to consider the influence of salts and electrolytes on the rheology of drilling fluid which has received less attention in the previous models. The advantage of this model is that it provides a description for the structural and orientation changes during transient and steady state fluid flows beside prediction of the transient and steady rheological behavior of salt containing suspensions of bentonite in polymeric solutions. Comparison of the model predictions with the published data from literature shows that the model predictions for the effects of the drilling fluid components including clay and salts are in well agreement with those of the rheological experimental data.

Rheological modeling of water based drilling fluids containing polymer/bentonite using generalized bracket formalism

Drilling fluids consist of several components with different physical and structural form which can be assumed as complex fluids. Optimum performance of drilling process could be obtained through the dynamic fluid computation which requires a reliable mathematical model capable to predict transient and steady state rheological behavior of drilling fluid. Generalized Newtonian formulations are the most popular models for drilling fluids due to their simplicity in spite of their inabilities to predict transient and elastic behavior of such fluids. In this paper, we have developed a mathematical model to predict transient and steady state rheological behavior of the complex fluids on the scale between the microscopic and macroscopic which is named mesoscopic scale. Constitutive and governing equations are obtained using the generalized bracket formalism which is based on the thermodynamics of flowing systems in that Hamiltonian mechanics has been used to describe the transport phenomena of internal microstructures. The model is developed for the suspension of bentonite/polymer dispersion and compared with experimental rheological data of different types of drilling fluids under transient and steady state condition. Comparison of model prediction with published data in the literature shows that the model is able to predict rheological behavior of bentonite muds satisfactorily.

Non-perturbative rheological behavior of a far-from-equilibrium expanding plasma

For the Bjorken flow we investigate the hydrodynamization of different modes of the one-particle distribution function by analyzing its relativistic kinetic equations. We calculate the constitutive relations of each mode written as a multi-parameter trans-series encoding the non-perturbative dissipative contributions quantified by the Knudsen Kn and inverse Reynolds Re−1 numbers. At any given order in the asymptotic expansion of each mode, the transport coefficients get effectively renormalized by summing over all non-perturbative sectors appearing in the trans-series. This gives an effective description of the transport coefficients that provides a new renormalization scheme with an associated renormalization group equation, going beyond the realms of linear response theory. As a result, the renormalized transport coefficients feature a transition to their equilibrium fixed point, which is a neat diagnostics of transient non-Newtonian behavior. As a proof of principle, we verify the predictions of the effective theory with the numerical solutions of their corresponding evolution equations. Our studies strongly suggest that the phenomenological success of fluid dynamics far from local thermal equilibrium is due to the transient rheological behavior of the fluid.

Irreversible time-dependent rheological behavior of cement slurries: Constitutive model and experiments

Over the last few decades, much focus has been given to investigating the reversible rheological behavior of thixotropic materials, but the description of the rheology of materials undergoing an irreversible process is still challenging. In this work, the time-dependent rheological behavior of a cement slurry is investigated. Different rheometric experiments are performed to evaluate the structure breakdown under shear, cement gelation, and curing process. A recently proposed thixotropic elasto-viscoplastic model [de Souza Mendes, Soft Matter 7, 2471–2483 (2011)] is modified to account for irreversible effects, which can be either of a chemical or physical nature, making the current model capable of describing reversible and irreversible processes with a single structure parameter. The parameters of the model are estimated from constant shear rate tests and from the flow curve of the fresh cement slurry. The model predictions are compared to step-down and step-up in stress experiments, and the results show that the model successfully describes experimental data obtained. Interesting phenomena are observed and discussed, including (i) thixotropic behavior during the dormant period, (ii) shear banding, (iii) irreversible changes in cement slurry rheology after the hydration reactions accelerate, and (iv) the existence of a characteristic time for the transition from a thixotropic-yield-stress material to a solid during curing. The predictive capability of the new model includes bifurcation, shear banding, stress overshoots, effects of chemical reactions, and irreversible shear degradation. It is argued that the ideas employed in the present work can be used to incorporate irreversible effects into other thixotropic models, giving rise to the possibility of describing the transient rheological behavior of complex materials in an unprecedented fashion.Over the last few decades, much focus has been given to investigating the reversible rheological behavior of thixotropic materials, but the description of the rheology of materials undergoing an irreversible process is still challenging. In this work, the time-dependent rheological behavior of a cement slurry is investigated. Different rheometric experiments are performed to evaluate the structure breakdown under shear, cement gelation, and curing process. A recently proposed thixotropic elasto-viscoplastic model [de Souza Mendes, Soft Matter 7, 2471–2483 (2011)] is modified to account for irreversible effects, which can be either of a chemical or physical nature, making the current model capable of describing reversible and irreversible processes with a single structure parameter. The parameters of the model are estimated from constant shear rate tests and from the flow curve of the fresh cement slurry. The model predictions are compared to step-down and step-up in stress experiments, and the results sho...

Transient Rheological Behavior of Semisolid SEED-Processed 7075 Aluminum Alloys in Rapid Compression

The transient rheological behavior and microstructure evolution of semisolid SEED-processed 7075 aluminum alloys were studied using the rapid compression tests. The effects of the TiB2 grain refinement on the grain morphology and size of semisolid slurries were investigated. Results indicated that the grain refiner could reduce the grain size and improve the globularity of α-Al grains. The grain-refined alloy can be easily deformed at a wide range of solid contents (0.42 to 0.53 Fs), in which the deformation level appears to be independent from the solid content. Under the transient state, the apparent viscosity decreased with increasing shear rate to a minimum value and followed by an increase as the shear rate decreased. The apparent viscosity of the base alloy exhibited a dependency on the solid content, while the apparent viscosity of the grain-refined alloy in the decreasing or increasing shear rate periods was not substantially influenced by the solid content. The viscosity as a function of applied shear rate can be described using the power law viscosity model. The differences in the flow behavior index (n) and the consistency index (k) for two alloys were discussed.

The transient behavior of soft glassy materials far from equilibrium

The transient structural and rheological behavior of soft glassy materials out of equilibrium is studied under small, medium, and large amplitude oscillatory shearing and interpreted via the fully quantitative sequence of physical processes (SPP) technique. We identify features of the local strain distribution that cause particular rheological responses and show that the SPP metrics accurately reflect the structural transitions. The SPP modulus is shown to reflect how much of the imposed strain is stored in the form of recoverable elastic strain, establishing it as an accurate measure of structural elasticity. We demonstrate the ability of the SPP scheme to accurately determine the amount of recoverable strain acquired in elastically dominated regimes by matching values estimated solely on the basis of the macroscopic stress to structural measures. In one case of large amplitude oscillatory shearing, the recoverable strain is shown to be around half a nondimensional strain unit by structural determination and from the SPP analysis, while the total imposed strain over the same interval is on the order of ten strain units. We therefore demonstrate the importance of separating the total and recoverable strains under strain-controlled conditions for the formation of accurate structure-property relations. We demonstrate how the alternating oscillatory state may be considered a consequence of a complex shear history. The results of this study show that the SPP scheme is a powerful tool for researchers wishing to understand the structural and rheological properties of soft glassy materials far from equilibrium.

Experimental and mathematical characterisation of the rheological instability of concentrated waste activated sludge subject to anaerobic digestion

For a proper operational performance assessment of excess sewage sludge digesters in practice, a better understanding of waste activated sludge (WAS) rheological behaviour is important, especially regarding the low-shear and poor mixing zones in anaerobic digesters. The potential rheological instability of WAS with different total solids (TS) concentrations was studied in this research. The obtained yield-pseudoplastic behaviour showed varying patterns in a wide shear rate range, of which characterisation depended on hybrid model fitting of defined shear rate segments. Although a new mathematical expression improved the fitting quality, limited applicability of the empiric models reflected the samples’ transient rheological behaviour rather than intrinsic properties, challenging the included parameters definition. Characterised by the distinct flow status and transitions, the observed rheological instability gives more insight in viscoelastic and thixotropic effects on sludge flow and mixing behaviour in full-scale WAS treatment systems. Recommendations for developing a rheological measurement protocol were also formulated.

Unusual Transient Network and Rheology of a Photoresponsive Telechelic Associative Model Polymer in Aqueous Solution Induced by Dimerization of Coumarin End Groups

Telechelic associative polymers (TAPs) can form a dynamic transient network in water and have been widely used as rheological modifiers for improving solution rheological properties in many industrial fields. In this work, we designed and prepared a novel photoresponsive coumarin-functionalized telechelic associative model polymer (CouTAP), which was used to investigate the influence of light-induced dimerization of coumarin end groups on the polymer structure and solution rheological properties. The effects of light intensity, irradiation time, polymer concentration, and temperature on the transient network and rheological behavior of the CouTAP aqueous solution were studied in detail. The rheological properties of the dimerized CouTAP aqueous solution show weak temperature dependence, and the dynamics hardly depends on concentration due to the transformation of triblock to multiblock polymers. A novel transient network model composed of train loops and bridges covalently linked to train loops was propos...

Fiber orientation prediction in nylon‐6 glass fiber composites using transient rheology and 3‐dimensional x‐ray computed tomography

In an attempt to relate transient rheology to 3‐dimensional fiber orientation, experimental testing on compression molded Nylon‐6 (PA‐6) containing 30% by weight short glass fibers (PA6‐30GF) and unfilled PA‐6 were carried out. On applying steady shear, PA6‐30GF samples displayed a transient viscosity overshoot while unfilled PA‐6 did not. The overshoot behavior has been attributed to the reorientation of fibers from an initial orientation to a steady state orientation. Samples subjected to different shear strain units were obtained from the rheometer by rapid cooling for morphological analysis. X‐ray Computed Tomography (X‐CT) was used to image samples to obtain 3‐dimensional fiber orientation and fiber concentration data. As the applied strain was increased, the second‐order orientation tensor was found to increase in the shearing direction and reduce in the radial and thickness directions. Experimental fiber orientation evolution data were compared with simulations from the Reduced Strain Closure (RSC) orientation model which is based on Folgar‐Tucker's orientation model. The interaction coefficient (Ci) and scalar reduction factor (K) which are parameters in the RSC model were fit using the experimental data. Currently available empirical expressions for determining the value of Ci were used to compare the experimental values. The experimental and predicted Ci values showed reasonable agreement which provided validation for the use of X‐CT as an experimental technique to determine fiber orientation distribution. The added benefit of obtaining fiber concentration data from X‐CT provides the opportunity to investigate the combined effects of fiber orientation and fiber concentration on transient rheological behavior of composites. POLYM. COMPOS., 40:E392–E398, 2019. © 2018 Society of Plastics Engineers

A jamming-like mechanism of yield-stress increase caused by addition of nonmagnetizable particles to magnetorheological suspensions

Particle-level simulations are employed to investigate the mechanism by which nonmagnetizable particles enhance the field-induced shear stress in magnetorheological fluids. Large amplitude oscillatory shear reveals that nonmagnetizable spheres increase the suspension stiffness; the transition to nonlinear deformation remains unaffected suggesting that the nonmagnetizable spheres do not alter the stability of the clusters of magnetizable spheres. Snapshots reveal that nonmagnetizable spheres participate in stress transfer via repulsive-force clusters in a mechanism similar to jamming in hard-sphere suspensions. Partial stresses, number of repulsive-force clusters, and transient rheological behavior further support that nonmagnetizable spheres directly enhance the stress via repulsive-force clusters. The repulsive-force clusters contain both magnetizable and nonmagnetizable spheres, which likely explains the observation that nonmagnetizable spheres enhance the magnetic field-induced stress, even though they are not magnetizable.

A new closure approximation based on the Cohen/Padé spring law and a novel method for its implementation

A new closure-approximated model based on the Cohen/Pade (CP) spring law is presented. Because it is inspired by the finitely extensible non-linear elastic Peterlin version (FENE-P), the model is titled CP-P. The rheological behaviors in simple and pressure-driven pipe shear flows in both the steady-state and time-dependent conditions are compared between the two models. To this end, a new approach based on the second moment Fokker–Planck equation instead of the Langevin equation is developed, which was confirmed by means of the existing analytical and stochastic data prior to its use. Application of this new approach is restricted to the closure approximated models but at a much less computational expense than the CONNFFESSIT-like simulations. In addition, the Brownian configuration field method is employed to make verification possible and more importantly, to shed light on the rheological performance of the CP model. According to the results, the CP-P model behaves similarly to the FENE-P model for the shear flows. The transient rheological behavior of the CP model is significantly different from that of the CP-P model, but both are the same in steady state.