Rheological Effects Research Articles

Strain-Controlled Critical Slowing Down in the Rheology of Disordered Networks.

Networks and dense suspensions frequently reside near a boundary between soft (or fluidlike) and rigid (or solidlike) regimes. Transitions between these regimes can be driven by changes in structure, density, or applied stress or strain. In general, near the onset or loss of rigidity in these systems, dissipation-limiting heterogeneous nonaffine rearrangements dominate the macroscopic viscoelastic response, giving rise to diverging relaxation times and power-law rheology. Here, we describe a simple quantitative relationship between nonaffinity and the excess viscosity. We test this nonaffinity-viscosity relationship computationally and demonstrate its rheological consequences in simulations of strained filament networks and dense suspensions. We also predict critical signatures in the rheology of semiflexible and stiff biopolymer networks near the strain stiffening transition.

Rheological and mechanical consequences of reducing the curing time of cold asphalt mixtures by means of magnetic induction

Cold asphalt mixtures are more sustainable because they are manufactured at ambient temperature. However, they are much less applied because they take longer time in the curing process due to the water contained in the asphalt emulsion, which delays the opening of roads. To solve this problem, the option of adding magnetic aggregates to cold asphalt mixtures and heating them by magnetic induction to evaporate the water contained in the asphalt emulsion and reduce curing time has been evaluated. For this objective, different by-products were evaluated as magnetic aggregate and the best one was selected. Four porous asphalt mixtures were then manufactured: an experimental mixture with the selected magnetic particles, a control mixture with virgin steel instead of the by-products, and two oven-cured reference mixtures without magnetic aggregate (one according to the Spanish standard and another according to the U.S. Asphalt Institute guidelines); then, the four mixtures were studied in terms of the curing process, rheological properties of bitumen and mechanical performance of samples. The experimental mixture containing industrial by-products shortened the curing time from 7 and 2 days (Spanish and U.S. Asphalt Institute standard, respectively) to only two hours; rheological and mechanical analysis proved the viability of this technology.

A novel thermo‐mechanically coupled material model for glass above the glass transition temperature

AbstractThin glass products have a giant field of application in several engineering branches such as for example, electronics, medical equipment, and the automotive industry. The non‐isothermal glass molding is a novel replicative glass processing technology enabling the realization of a cost‐efficient production of surface shapes with high accuracy and complexity. However, the application of this technology to thin glass production still causes shape distortions, cracks, and surface defects in molded parts. Therefore, these glass‐forming processes should be simulated by means of the combination of experimental investigation and mechanical modeling of glass above the glass transition temperature at finite strains. Previous experimental studies have shown that the Maxwell model is a reasonable approach for an appropriate prediction of the material behavior. Based on this viscoelastic formulation, a thermo‐mechanically consistent material law is used enabling the prediction of rheological effects noticed during the experiments. More specifically, the relaxation behavior can be described by a stress‐dependent relaxation time and the dissipation generated is considered as well. Furthermore, isothermal uniaxial compression tests above the glass transition temperature are conducted for different strain rates and temperatures within the experimental investigation. Combining the experimental data with the simulation, a multi‐curve‐fitting leads to suitable material parameters with respect to distinct temperatures employing a nonlinear optimization.

Effect of rheology and cooling on paste extrusion using texture analysis

Extrusion of pastes from squeezable tubes is a ubiquitous but complex process, and it is not well studied. A common example is toothpaste, which needs to be easily extrudable from its tube, but it is not always the case due to the complex rheology of the paste. This may be particularly problematic if the base liquid in the formula is anhydrous leading to the paste hardening at temperatures close to ambient. In this work, we use various testing techniques to study the squeezability of the tubes containing hydrous and anhydrous paste formulations. We show that mechanical testing imitating human hand operation adequately predicts the actual sensorial panel data while also correlating with simple viscosity measurements. Furthermore, for anhydrous pastes sensitive to cooling their effective hardening temperature may be predicted by thermal analysis of their base liquids. Overall, it is expected that the results and the methodologies presented in this work will be of good guidance for product/packaging developers.

High-internal-phase emulsions stabilized by alkali-extracted green tea polysaccharide conjugates for curcumin delivery

Exploring the emulsification capabilities of tea polysaccharide conjugates (TPCs) in high-internal-phase emulsions (HIPEs) would further expand the utilization value of TPCs. This study aimed to prepare 0.1–0.5 wt% alkali-extracted green tea polysaccharide conjugate (gTPC-A)-stabilized HIPEs containing 75–87 wt% medium chain triglycerides (MCTs) to investigate their stability, rheology, microstructure, and loading and protective effects on curcumin. The findings revealed that only 0.1 wt% of gTPC-A could stabilize HIPEs containing 85 wt% oil for 30 days. HIPEs had better storage stability in a weakly acidic environment at pH 5.0–6.0 and at temperatures less than 70 °C. HIPEs could load curcumin and protect it from ultraviolet (UV) radiation and in vitro digestion. The half-life of curcumin loaded in HIPEs was 65 h under UV radiation. The curcumin bioaccessibility of HIPEs (56.29 %) was higher than that in MCT (8.73 %). These results provided a theoretical basis for the extensive use of TPCs.

Penetrating gunshots to the head after close-range shooting: Dynamics of waves and the effect of brain tissue rheology

Formation of the brain tissue backspatter after penetrating gunshots to the head is preceded and driven by formation and evolution of the bullet channel, which is filling with air and/or muzzle gases or issuing them with tissue fragments or without them. This process is explored here in a model situation in the framework of the dynamics of waves in brain tissue affected by its realistic rheological behavior, fragmentation, and gas dynamics in the evolving bullet channel. As a rheological model of the brain tissue, a new strain-energy function W, introduced in the accompanying work, is employed, which expresses the strain energy as a rational function of the principal invariants of the Cauchy tensor C. This strain-energy function W generates a hyperelastic constitutive equation, which resembles the behavior of brain tissues, i.e., reveals a much stronger resistance to compression than to stretching and strongly nonlinear response in simple shear. This new rheological model belongs to the class of hyperelastic models used for description of hydrogels. The equations of motion supplemented by this rheological model reveal the dynamics of the compression and rarefaction waves propagating through the brain tissue following the formation of the bullet channel. These waves are reflected from the skull and the bullet channel. In parallel, gas dynamics of air and/or muzzle gases flowing into or issued outward of the bullet channel, and stretching-driven fragmentation of the brain tissue are evolving in concert with the wave dynamics in the brain tissue. This allows for prediction of backspatter of the brain tissue resulting from a short-range shooting.

2D stress rotation in the Tonga subduction region

Despite their enigmatic origins, deep earthquakes provide unique information about the stress distribution in slabs. Down-dip compression is expected at depth, due to resistance from endothermic phase transition near 660 km and increasing viscosity. Focal mechanisms for ordinary deep (620-680 km) earthquakes in the Tonga subduction zone exhibit down-dip compressional stresses in agreement with this expectation, but unusually deep (≥ 680 km) earthquakes exhibit vertical tension and horizontal compression. Here we present a numerical modelling study of the Tonga slab focused on stress patterns in the transition zone. The subducting Pacific plate is one of the oldest and thus coldest plates in the world, so our parametric study tests the effects of rheology and phase transitions on stress evolution for an exceptionally cold subducting plate. Our results suggest that direct buoyancy effects from the endothermic phase transition at 660 km depth are overprinted by bending-related forces. A stress pattern best fitting seismogenic stresses is found for the coldest tested subducting plate (150 Myr old) and a viscosity interface decoupled from the 660-km phase transition and shifted to 1000-km depth. An abrupt change of stress orientations is observed when the slab, temporarily deflected by the phase transition, penetrates to the shallow lower mantle and the fold of the flat-lying part is tightening.

Global characterization of hydrodynamics and gas-liquid mass transfer in a thin-gap bubble column in presence of Newtonian or non-Newtonian liquid phase

Bubble columns are commonly used as photobioreactors (PBRs) due to their good mixing and mass transfer capabilities. Modification in design and operating parameters are nevertheless needed to intensify volumetric productivity. Thin-gap bubble column can be used in this context to operate with high biomass concentration, up to conditions where the culture becomes non-Newtonian. In the present study, the global hydrodynamics and gas–liquid mass transfer inside a 4 mm thickness thin-gap bubble column are characterized in presence of low viscosity Newtonian fluid (water) and two aqueous solutions of Carboxymethyl Cellulose and Xanthan Gum. These shear-thinning solutions are used to mimic high concentration cultures of Chlorella Vulgaris at 42 g.L−1. A range of superficial gas velocities and different capillary diameters are explored to investigate the effect of sparging on hydrodynamics and gas–liquid mass transfer. Studied parameters are flow regimes, mixing, and gas–liquid mass transfer. Results are compared with literature results in classical bubble columns to put into evidence the original effects of both confinement and liquid rheology. Among others, these results show that compared to Newtonian media, non-Newtonian media result in higher gas holdup and mixing times and a lower gas–liquid mass transfer coefficient. The findings suggest that the presence of smaller bubbles would improve mass transfer due to the increased interfacial area, while the presence of larger bubbles would improve mixing performance due to increased vorticity in their wake and relatively greater species transport.

Effects of fluid rheology on dynamics of a capsule through a microchannel constriction

This paper numerically investigates the impact of fluid rheology on the behaviors of a spherical capsule through a microchannel constriction. Different flow scenarios are considered: a Newtonian capsule in a viscoelastic matrix, a Newtonian capsule in a Newtonian matrix, and a viscoelastic capsule in a Newtonian matrix. The results demonstrate that the capsule's lengths undergo oscillations during the passage through the constriction, with three stages of evolution. When approaching the constriction, the capsule respectively experiences increase and decrease in its length and height. While within or exiting the constriction, the length of the capsule continuously decreases, and the height generally increases. As the capsule moves away from the constriction, the capsule relaxes to different profiles in different flows. Detailed analysis on the effects of the fluid viscoelasticity on the capsule's lengths in different stages is provided. In addition, the behaviors of a red blood cell passing through a microchannel constriction are also examined. This study sheds light on the complex behaviors of a spherical capsule and red blood cell in microchannel constriction, emphasizing the significant influence of fluid rheology on their deformation and shape changes.

Fluid-inertia torque on spheroids in pseudo-plastic fluid flows: effect of shear-thinning rheology

Fluid-inertia torque remarkably affects the orientation of non-spherical particles in Newtonian flows whereas this torque induced by convective fluid inertia in particle-laden pseudo-plastic flows is still unknown. In the present study we numerically investigate the fluid-inertia torque on a neutrally buoyant spheroid in the Carreau-type pseudo-plastic fluid flows at finite Reynolds numbers with the immersed boundary method. The results show that compared with the fluid-inertia torque in Newtonian flows, the magnitude of the fluid-inertia torque on spheroids is remarkably attenuated by the shear-thinning rheology in pseudo-plastic fluid flows. The deviation of fluid-inertia torque between pseudo-plastic and Newtonian flows is more significant with decreasing Reynolds numbers, indicating the importance of the effect of shear-thinning rheology at small Reynolds numbers. Moreover, the spheroid rotation rate is reduced in pseudo-plastic fluids, and the equilibrium orientation of oblate spheroids changes non-monotonically with the shear-thinning effect in the linear shear flow of pseudo-plastic fluids. The present findings imply the importance of the effect of shear-thinning rheology on the torques of spheroids, which could be potentially applied for the control of particle orientations in pseudo-plastic fluids in the future.

Experimental Study on the Dilatancy and Energy Evolution Behaviors of Red-Bed Rocks under Unloading Conditions.

Surrounding rock deformation and consequent support failure are the most prominent issues in red-bed rock tunnel engineering and are mainly caused by the effects of unloading, rheology, and swelling. This study investigated the mechanical responses of two kinds of red-bed mudstone and sandstone under unloading conditions via laboratory observation. Volume dilation was observed on the rocks during unloading, and the dilatancy stress was linear with the initial confining pressure. However, the ratios of dilatancy stress to peak stress of the two rocks kept at a range from 0.8 to 0.9, regardless of confining pressures. Both the elastic strain energy and the dissipated energy evolved synchronously with the stress-strain curve and exhibited conspicuous confining pressure dependence. Special attention was paid to the evolution behavior of the dilatancy angle. The dilatancy angle changed linearly during unloading. When the confining pressure was 10 MPa, the dilatancy angle of mudstone decreased from 26.8° to 12.5° whereas the dilatancy angle of sandstone increased from 34.6° to 51.1°; when the confining pressure rose to 25 MPa, the dilatancy angle of mudstone and sandstone decreased from 45.8° to 17.4° and increased from 21.7° to 39.5°, respectively. To further understand the evolution of the dilatancy angle, we discussed the links between the variable dilatancy angle and the processes of rock deformation and energy dissipation.

Role of interfacial rheology on fingering instabilities in lifting Hele-Shaw flows.

The lifting Hele-Shaw cell setup is a popular modification of the classic, fixed-gap, radial viscous fingering problem. In the lifting cell configuration, the upper cell plate is lifted such that a more viscous inner fluid is invaded by an inward-moving outer fluid. As the fluid-fluid interface contracts, one observes the rising of distinctive patterns in which penetrating fingers having rounded tips compete among themselves, reaching different lengths. Despite the scholarly and practical relevance of this confined lifting flow problem, the impact of interfacial rheology effects on its pattern-forming dynamics has been overlooked. Authors of recent studies on the traditional injection-induced radial Hele-Shaw flow and its centrifugally driven variant have shown that, if the fluid-fluid interface is structured (i.e., laden with surfactants, particles, proteins, or other surface-active entities), surface rheological stresses start to act, influencing the development of the viscous fingering patterns. In this paper, we investigate how interfacial rheology affects the stability as well as the shape of the emerging fingered structures in lifting Hele-Shaw flows, at linear and early nonlinear dynamic stages. We tackle the problem by utilizing the Boussinesq-Scriven model to describe the interface and by employing a perturbative mode-coupling scheme. Our linear stability results show that interfacial rheology effects destabilize the interface. Furthermore, our second-order findings indicate that interfacial rheology significantly alters intrinsically nonlinear morphological features of the shrinking interface, inducing the formation of narrow sharp-tip penetrating fingers and favoring enhanced competition among them.

A two-dimensional double layer-averaged model of hyperconcentrated turbidity currents with non-Newtonian rheology

Hyperconcentrated turbidity currents typically display non-Newtonian characteristics that influence sediment transport and morphological evolution in alluvial rivers. However, hydro-sediment-morphological processes involving hyperconcentrated turbidity currents are poorly understood, with little known about the effect of the non-Newtonian rheology. The current paper extends a recent two-dimensional double layer-averaged model to incorporate non-Newtonian constitutive relations. The extended model is benchmarked against experimental and numerical data for cases including subaerial mud flow, subaqueous debris flow, and reservoir turbidity currents. The computational results agree well with observations for the subaerial mud flow and independent numerical simulations of subaqueous debris flow. Differences between the non-Newtonian and Newtonian model results become more pronounced in terms of propagation distance and sediment transport rate as sediment concentration increases. The model is then applied to turbidity currents in the Guxian Reservoir planned for middle Yellow River, China, which connects to a tributary featuring hyperconcentrated sediment-laden flow. The non-Newtonian model predicts slower propagation of turbidity currents and more significant bed aggradation at the confluence between the tributary Wuding River and the Yellow River in the reservoir than its Newtonian counterpart. This difference in model performance could be of considerable importance when optimizing reservoir operation schemes.

Investigating the time-varying effect and accurate measurement method of wet shotcrete rheology based on eBT2 rheometer

An appropriate amount of air-entraining agent improves the wet shotcrete fluidity, and the accurate measurement of rheological parameters accurately expresses the rheological characteristics of sprayed concrete. In this paper, eBT2 rheometer was used to measure time variation of rheological parameters of high air content wet shotcrete (HACWS). At the same time, in order to investigate measurement accuracy of shotcrete rheology, the influence of rheometer operating modes (OM) on rheological parameters was studied. This paper selected four rheometer OM to comprehensively analyze the rheological characteristics and rheometer measurement accuracy of HACWS. The results showed that relative plastic viscosity (RPV) and relative yield stress (RYS) of HACWS both tended to decrease first and then increase with time. The torque measured by eBT2 rheometer remained constant at high shear rates. The rheological parameters obtained with different OM differed significantly, and OM-B was recommended to analyze the rheological properties of fresh concrete. This paper provides a reference for the selection of air-entraining agent type and rheometer OM.

Effects of Composite Rheology on Plate‐Like Behavior in Global‐Scale Mantle Convection

AbstractEarth's upper mantle rheology controls lithosphere‐asthenosphere coupling and thus surface tectonics. Rock deformation experiments and seismic anisotropy measurements indicate that composite rheology (co‐existing diffusion and dislocation creep) occurs in the Earth's uppermost mantle, potentially affecting convection and surface tectonics. Here, we investigate how the spatio‐temporal distribution of dislocation creep in an otherwise diffusion‐creep‐controlled mantle impacts the planform of convection and the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection self‐generating plate‐like tectonics. The low upper‐mantle viscosities caused by zones of substantial dislocation creep produce contrasting effects on surface dynamics. For strong lithosphere (yield strength > 35 MPa), the large lithosphere‐asthenosphere viscosity contrasts promote stagnant‐lid convection. In contrast, the increase of upper mantle convective vigor enhances plate mobility for lithospheric strength <35 MPa. For the here‐used model assumptions, composite rheology does not facilitate the onset of plate‐like behavior at large lithospheric strength.

On the rheological, fresh and strength effects of using nano-silica added geopolymer grout for grouting columns

In this article, the influence of nano-silica (NS) added geopolymer-based grout (GBG) mixtures for use in grouting columns was investigated experimentally. For this purpose, the rheological characteristics (shear stress, apparent viscosity, yield stress, plastic viscosity and rheological behaviour) of GBG mixtures obtained with nano-silica (NS) together with fly ash (FA) replacements were measured at a wide range of NS dosages of 0% (only FA for control), 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, and extensive effects of water to binder (w/b) ratios (w/b = 0.50, 0.75, 1.00, 1.25, and 1.50), by dry weight. From a proper and common consistency of water effects (w/b = 1.00), the fresh state properties (mini-slump, Marsh funnel viscometer and bleeding) and unconfined compressive strength (UCS) performance of geopolymer grouting columns were tested. Results of the study indicated that incorporating NS into GBG mixtures had positive effects on the rheological characteristics. The mini-slump and flow time of the Marsh funnel increased slightly with NS dosages up to the rate of 1.5% while increasing the NS proportions led to a reduction of bleeding that was prominent beyond 1.5%NS. Among the treatments of geopolymer mixtures with NS, the highest UCS performance was obtained at the dosage rate of 1.5%NS.

Study on the consolidation behavior of horizontal drainage foundation under complex aquifer formation conditions in karst regions

Introduction: The consolidation behavior of horizontal drainage foundation under complex aquifer conditions in karst areas is a hot topic in the field of geotechnical engineering.Methods: This paper presents a modified piecewise-linear model for plane-strain consolidation. In this model, the distributed drainage boundary was used to describe the drainage performance of soil layer boundaries, and the UH model considering the time effect was selected to reflect soil’s rheological property. Through comparison with existing research, the validity of the calculation model in this paper was verified. Then several examples were used to analyze the consolidation behavior of the foundation under the combined action of rheological effect and distributed drainage boundaries.Results and discussion: Numerical studies show that the phenomenon of the increase of excess pore pressure exists in the foundation of the distributed drainage boundary after considering the rheology in the early stage of consolidation. Moreover, the larger the secondary consolidation coefficient and the initial over-consolidation parameter, or the smaller the pave rate and the thickness-width ratio, the above phenomenon is more obvious. In terms of the dissipation of the pore water pressure, the larger the secondary consolidation coefficient and the initial over-consolidation parameter, the slower the pore pressure dissipation, and the smaller the pave rate or the thickness-width ratio can achieve the above effects. In terms of the impact on settlement, the above-mentioned parameters are consistent, that is, the larger the corresponding parameter, the larger the corresponding settlement value.

A numerical study on the impact of lubricant rheology and surface topography on heavily loaded non-conformal contacts

The increasing requirement of high-power density (power throughput/ weight) in modern day machines lead to thin film lubrication condition in various machine components (rolling element bearings, gears, cams, etc,) due to severe loading conditions. Surface roughness features and lubricant rheology plays a vital role in thin film lubrication, and significantly affects the lubrication performance and lifetime of machine components. The present work demonstrates surface topography and lubricant rheology effects on the traction coefficient for heavily loaded non-conformal contacts. The load-sharing concept considering elastic-plastic deformation of asperities, and Carreau shear-thinning rheological model is employed to describe the dry rough contacts and non-Newtonian behavior of lubricant. An influence of surface topography parameters such as roughness, skewness, kurtosis, and pattern ratio on the traction coefficient is discussed. From results, it is found that among different surface topographies, negatively skewed surfaces having isotropic surface pattern exhibit minimum traction coefficient. The load share function and the critical rolling speed are determined for various surface topographies which provides further insights into the surface topography effect on traction coefficient. The findings of present study are noteworthy as they provide a theoretical basis for an assessment of the lubrication performance of heavily loaded non-conformal contacts.

Effect of Multiple-Walled Carbon Nanotubes (MWCNTs) on Asphalt Binder Rheological Properties and Performance

Growing traffic loads, soaring summer temperatures, and moisture damage will render conventional asphalt binder insufficient to maintain the performance standards of asphalt concrete pavement. Thus, it is necessary to modify the virgin asphalt using various polymers or nanomaterials. The primary goal of this research was to examine the rheological effects of combining multiple-walled carbon nanotubes (MWCNTs) and styrene butadiene styrene (SBS) in an asphalt binder. In this study, MWCNTs and SBS were mixed with virgin asphalt at concentrations of 1%, 3%, and 5% by weight. The performance grade (PG) and asphalt binder qualities were determined through Superpave system testing. The addition of 1% MWCNTs had no effect on the (PG) of virgin asphalt, whereas the addition of 3% and 5% MWCNTs resulted in increases of 2° and 4°, respectively. When 1% SBS is added to asphalt, the PG rises by an average of 1°; when 3% and 5% SBS are used, the PG rises by an average of 2° and 3°, respectively. The results also showed that the rutting parameter (G ∗ /sin) increased by 10%, 73%, and 208% when asphalt was changed with 1%, 3%, and 5% of SBS, and by 18% and 130% when MWCNTs were applied.

An evaluation of fiber-based lost circulation material for fracture plugging using simulations

Lost circulation during drilling operations is a major problem owing to the prolonged non-productive time, especially in naturally fractured reservoirs. Incorporating granular lost circulation materials (LCM) in the drilling mud has been the traditional first-approach method with the industry moving towards incorporating fibers and flaky LCMs with the goal of improving the fracture sealing effectiveness of the LCM blends. Although the fracture sealing mechanism and the particle transport for granular LCMs are well understood, there is limited knowledge on the behavior of fibers as LCMs in flows governed by high differential pressures at the bottomhole. Further, considering limited lab studies to understand the effectiveness of fiber LCMs, we tried to fill this gap by developing and using coupled numerical models that are now able to incorporate the axial and bending deformations of fibers to assess the impact of different design parameters. We evaluate the effects of fluid rheology, the LCM concentration, fiber stiffness, interparticle friction, and fracture roughness on fracture sealing. The mechanism driving fracture sealing in fiber-based LCM is vastly different from the proposed mechanisms for granular LCM. Bridge initiation in fiber-LCM originates with ‘initial fiber jamming’ leading to consecutive fibers further being trapped forming a net-like entrapment that further impedes and retains incoming particles. The ability of this initial bridge initiation to develop into a complete seal is dependent on several factors. The presented model provides an initial assessment tool for evaluating the significance of different LCM parameters for effective fracture sealing. We attempt to showcase the importance and reliability of bringing coupled simulation techniques into the domain for effective fiber LCM evaluation with the results of our work.