Rheological Evolution Research Articles

Use of MRI as a predictive tool for physicochemical and rheologycal features during cured ham manufacturing

Magnetic resonance imaging (MRI) was used to study the structural changes during dry-cured ham manufacturing. T1, T2 and apparent diffusion coefficient (ADC) were determined. Dry cured hams were analysed at different steps of the manufacturing process (raw, salted, post salted, half-cured and cured). Structural changes were linked with the rheological behaviour, estimated by texture profile analysis (TPA) performed in three different muscles of hams (semimembranosus, semitendinosus and biceps femoris). A decrease for T1, T2 and ADC parameters during the curing process was observed, connected to the dehydration kinetics and salt diffusion. Curing process increased hardness and chewiness and reduced elasticity and cohesiveness. Mathematical models were defined to obtain useful equations to monitor ripening. Multiple and simple linear regression models were performed to predict water and salt content and rheological features evolution through MRI parameters. Best settings were achieved with water and salt content for the three studied muscles (R2 around 0.90). T1, T2 and ADC showed a negative correlation with hardness and a positive relation with springiness and cohesiveness.

Equilibrium Viscosity and Disequilibrium Rheology of a high Magnesium Basalt from Piton De La Fournaise volcano, La Reunion, Indian Ocean, France

Lava flows are a common hazard at basaltic to intermediate volcanoes in general and have posed a significant threat to La Reunion Island specifically over the past centuries. In sustained flow units, the efficiency of lava transport away from the vent is dominated by cooling. For basaltic to intermediate lavas it is the ability of the lava to solidify during cooling which exerts a first-order control on the extent of flow. As a consequence, understanding the sub-liquidus rheology of lavas has become a key focus in lava flow research in the past decade. To date, a systematic understanding of lava rheology during emplacement conditions has been largely hampered by a lack of experimental data. Here we present new data on the rheological evolution of a crystalizing high Mg basalt from Piton de la Fournaise. Sub-liquidus experiments were performed at constant cooling rates of 0.5 to 5 K/min, to mimic conditions similar to those experienced by lava during flow on the surface and magma during dike and sill emplacement. The data show that the effective viscosity of the crystallizing suspension increases until reaching a specific sub-liquidus temperature, the so-called “rheological cut-off temperature” (T cutoff ), at which the lava effectively solidifies. This departure to high viscosity is a consequence of rapid crystallization and is found to be primarily controlled by the imposed cooling-rate. Based on our experimental data, we adapt the failure forecasting method (FFM), which is commonly used to describe the self-accelerating nature of seismic signals to forecast material failure, to predict the rheological cut-off temperature (T cutoff ). The data presented serve to expand the modest existing experimental database on non-equilibrium rheology of lavas as a step towards understanding the underlying process dynamics.

Time Evolution of Rheology of Cement Pastes Affected by Mixture Design and Mixing Procedure

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.

Investigation of the rheological behavior of activated sludge in response to CeO2 nanoparticles and potential mechanism.

With the rapid development of CeO2 nanoparticles (NPs), the released CeO2 NPs entering into wastewater treatment plants might bring the challenges for sludge pumping and mixing. In this study, we firstly elucidated the rheological behavior of 4.0wt% sludge at various concentrations of CeO2 NPs. With the increase of CeO2 NPs to 5mg/L, the shear stress at any given shear rate was reduced and the limiting viscosity was also decreased, indicating the sludge became more flowability. The dynamic sweep tests further demonstrated the decreased elastic behavior and weakened internal structure in response to low concentrations of CeO2 NPs (≤ 5mg/L). However, 20mg/L CeO2 NPs had negative effects on the rheological evolution of sludge, namely, better solid-like property and higher elastic structure. These results were mainly attributed to the combination of the decreased β-D-glucopyranose polysaccharides which support the rigid structure of sludge and the dramatically increased protein content (especially in 20mg/L CeO2 NPs). These results can potentially provide novel information for the efficient design of sludge treatment when coped with CeO2 NPs. Graphical abstract ᅟ.

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.

Rheological Evolution of Ti-Bearing Slag with Different Volume Fractions of TiN

The effect of the volume fraction of TiN (0 to 4.27 vol pct) on the rheological behaviors of Ti-bearing slag, including the viscosity and the constitutive equation, was investigated using a Brookfield rheometer at 1773 K. With the increasing TiN, the viscosity and the shear stress increased substantially, and the slag is converted from Newtonian to non-Newtonian. When the slag samples were dispersed with TiN (1.00 to 4.27 vol pct), the measured viscosities were greater than those estimated by the Einstein–Roscoe equation, and the complex internal structure was suggested to be responsible for the extra enhancement of the viscosity beyond that caused by TiN itself. The viscosity curves of the slag samples containing TiN (1.00 to 4.27 vol pct) were divided into three regions depending on the critical shear rate and the initial shear rate. In the Newtonian region, the apparent volume fraction of TiN was defined and used to develop a semiempirical model based on the Einstein–Roscoe equation to describe the viscosity. In the two non-Newtonian regions, the shear rate, the yield stress, and the viscosity differences between the non-Newtonians regions and the Newtonian regions were applied in developing the viscosity models.

Processes controlling the downstream evolution of ice rheology in glacier shear margins: case study on Rutford Ice Stream, West Antarctica

ABSTRACTIce rheology governs how glaciers flow and respond to environmental change. The rheology of glacier ice evolves in response to a variety of mechanisms, including damage, heating, melting and the development of crystalline fabric. The relative contributions of these rheological mechanisms are not well understood. Using remotely sensed data and physical models, we decouple the influence of each of the aforementioned mechanisms along the margins of Rutford Ice Stream, a laterally confined outlet glacier in West Antarctica. We show that fabric is an important control on ice rheology in the shear margins, with an inferred softening effect consistent with a single-maximum fabric. Fabric evolves to steady state near the onset of streaming flow, and ice progressively softens downstream almost exclusively due to shear heating. The rate of heating is sensitive to local shear strain rates, which respond to local changes in bed topography as ice is squeezed through the basal trough. The impact of shear heating on the downstream evolution of ice rheology in a laterally confined glacier suggests that the thermoviscous feedback – wherein faster ice flow leads to higher rates of shear heating, further softening the ice – is a fundamental control on glacier dynamics.

Crystallisation in basaltic magmas revealed via in situ 4D synchrotron X-ray microtomography

Magma crystallisation is a fundamental process driving eruptions and controlling the style of volcanic activity. Crystal nucleation delay, heterogeneous and homogeneous nucleation and crystal growth are all time-dependent processes, however, there is a paucity of real-time experimental data on crystal nucleation and growth kinetics, particularly at the beginning of crystallisation when conditions are far from equilibrium. Here, we reveal the first in situ 3D time-dependent observations of crystal nucleation and growth kinetics in a natural magma, reproducing the crystallisation occurring in real-time during a lava flow, by combining a bespoke high-temperature environmental cell with fast synchrotron X-ray microtomography. We find that both crystal nucleation and growth occur in pulses, with the first crystallisation wave producing a relatively low volume fraction of crystals and hence negligible influence on magma viscosity. This result explains why some lava flows cover kilometres in a few hours from eruption inception, highlighting the hazard posed by fast-moving lava flows. We use our observations to quantify disequilibrium crystallisation in basaltic magmas using an empirical model. Our results demonstrate the potential of in situ 3D time-dependent experiments and have fundamental implications for the rheological evolution of basaltic lava flows, aiding flow modelling, eruption forecasting and hazard management.

Re-folded structure of syn-orogenic granitoids (Padrón dome, NW Iberia): Assessing rheological evolution of cooling continental crust in a collisional setting

This contribution discusses about the rheological, kinematic and dynamic frameworks necessary to produce recumbent and upright folds from syn-orogenic granitic massifs that were formed during an early stage of magma genesis related to the onset of a migmatitic dome. Syn-kinematic granitoids occurring within the high-grade infrastructure of the Padrón migmatitic dome (NW Iberia) are deformed into large-scale recumbent folds (D2) that are later affected by upright folds (D3). Petrostructural analysis of a selected area of this dome reveals that after a period of crustal thickening (D1), NNW-directed extensional flow gave way to recumbent folds and penetrative axial plane foliation (S2). Superimposed subhorizontal compression resulted in upright folds (D3). A closer view into the dynamics of the dome allows exploring the factors that may condition the nucleation of folds with contrasting geometries during progressive deformation of molten continental crust. The formation of folds affecting syn-kinematic granitoids suggests a cooling metamorphic path in migmatitic domes. Active and passive folding mechanisms require a crystallizing (cooling) magma to nucleate folds. A more competent metamorphic host inhibits fold nucleation from much less competent magmas. As it crystallizes, magma becomes more rigid (competent), and approaches viscosity values of its host. Passive folding is favored when no significant competence contrast exists between magma and host, so this folding mechanism is more likely shortly after magma genesis and emplacement. In such conditions, and under dominant subhorizontal flow accompanied by flattening (D2), passive folding would produce isoclinal recumbent geometries. Further magma cooling introduces a shift into the rheological behavior of partially molten crust. Thereon, crystallizing magma bodies would represent significant competence contrasts relative to their host. At this point, buckling is a more likely folding mechanism, and more regular, buckle folds re-fold previous structures after significant cooling. The geometry of resulting folds is upright due to dominant subhorizontal compression (D3) at this stage.

Evolution of molecular packing and rheology in asphalt binder during rejuvenation

Effective rejuvenators that restore the thermo-mechanical properties of aged asphalt would extend pavement service life and increase utilization of recycled material, cutting material and environmental costs. However, the efficacy and mechanism of action need to be characterized in order to optimize rejuvenator formulation and dosage. This study introduces the RIPS method (Rejuvenation Index based on Polydispersity and Stiffness) which applies rheological characterization to build a simple model for examining and predicting the effect of rejuvenation on the rheology, polydispersity, and microstructure of aged asphalt binder. RIPS showed that addition of a specific bio-rejuvenator significantly improved the low-temperature properties of highly aged binder. The method accurately predicted the binder relaxation modulus and could calculate the exact rejuvenator dosage needed to restore the performance grade to specification. The rejuvenation mechanism was further examined using DSC, FTIR, and quantum level computational modeling, which found that polar chemical groups in the bio-rejuvenator could be responsible for solubilizing similar polar groups in aged binder leading to reduced molecular aggregate size and restoration of the thermo-mechanical properties of aged binder. These results provide insight into the molecular mechanisms of rejuvenation and offer a path towards more rational design and deployment of rejuvenator formulations.

The impact of hydrodynamics on viscosity evolution in colloidal dispersions: Transient, nonlinear microrheology

Evolution of microstructure and rheology during flow startup, and its connection to microscopic transport processes, is studied theoretically via active microrheology. At steady state, the balance between entropic, hydrodynamic, and other forces changes with flow strength, producing sustained microstructural asymmetry and non‐Newtonian rheology. However, the transition from equilibrium to steady flow is sometimes marked by overshoots in viscosity that suggests a temporally evolving competition between these rate processes. Here, we formulate and solve a Smoluchowski equation for the time‐dependent evolution of particle microstructure induced by the motion of a colloidal probe driven through a bath of colloidal spheres. The structure is then utilized to compute the time‐dependent microviscosity. Brownian diffusion always sets short‐time particle dynamics, which hinders maturation of the boundary layer. The disparity in Brownian and advective transport rates produces a reversal from flow thinning to flow thickening during startup, revealing that non‐Newtonian flow phenomenology is not instantaneously established. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3198–3214, 2018

The effect of oxygen fugacity on the rheological evolution of crystallizing basaltic melts

Storage and transport of silicate melts in the Earth's crust and their emplacement on the planet's surface occur almost exclusively at sub-liquidus temperatures. At these conditions, the melts undergo crystallization under a wide range of cooling-rates, deformation-rates, and oxygen fugacities (fO2). Oxygen fugacity is known to influence the thermodynamics and kinetics of crystallization in magmas and lavas. Yet, its influence on sub-liquidus rheology remains largely uncharted.We present the first rheological characterization of crystallizing lavas along natural cooling paths and deformation-rates and at varying fO2. Specifically, we report on apparent viscosity measurements for two crystallizing magmatic suspensions 1) at log⁡fO2 of −9.15 (quartz–fayalite–magnetite buffer, QFM, −2.1) and 2) in air. These fugacities span a range of reduced to oxidized conditions pertinent to magma migration and lava emplacement. We find that: 1) crystallization at constant cooling-rates results in a quasi-exponential increase in the apparent viscosity of the magmatic suspensions until they achieve their rheological cut off temperature (Tcutoff), where the melt effectively solidifies 2) the rheological departure and Tcutoff increase with increasing fO2 and 3) increasing fO2 results in decreased crystallization-rates. Based on the experimental results and by comparison with previous rheological isothermal studies we propose a generalisation of the effect of fO2 on the dynamic rheological evolution of natural magmatic and volcanic suspensions. We further discuss the implications for magmatic transport in plumbing and storage systems (e.g. conduits, dikes and magma chambers) and during lava flow emplacement.

Multiple particle tracking microrheology measured using bi-disperse probe diameters.

Multiple particle tracking microrheology (MPT) is a powerful tool for quantitatively characterizing rheological properties of soft matter. Traditionally, MPT uses a single particle size to characterize rheological properties. But in complex systems, MPT measurements with a single size particle can characterize distinct properties that are linked to the materials' length scale dependent structure. By varying the size of probes, MPT can measure the properties associated with different length scales within a material. We develop a technique to simultaneously track a bi-disperse population of probe particles. 0.5 and 2 μm particles are embedded in the same sample and these particle populations are tracked separately using a brightness-based squared radius of gyration, Rg2. Bi-disperse MPT is validated by measuring the viscosity of glycerol samples at varying concentrations. Bi-disperse MPT measurements agree well with literature values. This technique then characterizes a homogeneous poly(ethylene glycol)-acrylate:poly(ethylene glycol)-dithiol gelation. The critical relaxation exponent and critical gelation time are consistent and agree with previous measurements using a single particle. Finally, degradation of a heterogeneous hydrogenated castor oil colloidal gel is characterized. The two particle sizes measure a different value of the critical relaxation exponent, indicating that they are probing different structures. Analysis of material heterogeneity shows measured heterogeneity is dependent on probe size indicating that each particle is measuring rheological evolution of a length scale dependent structure. Overall, bi-disperse MPT increases the amount of information gained in a single measurement, enabling more complete characterization of complex systems that range from consumer care products to biological materials.

The Rheological Evolution of Brittle‐Ductile Transition Rocks During the Earthquake Cycle: Evidence for a Ductile Precursor to Pseudotachylyte in an Extensional Fault System, South Mountains, Arizona

AbstractWe investigate how the rheological evolution of shear zone rocks from beneath the brittle‐ductile transition (BDT) is affected by coeval ductile shear and pseudotachylyte development associated with seismicity during the earthquake cycle. We focus our study on footwall rocks of the South Mountains core complex, and we use electron backscatter diffraction (EBSD) analyses to examine how strain is localized in granodiorite mylonites both prior to and during pseudotachylyte development beneath the BDT. In mylonites that are host to pseudotachylytes, deformation is partitioned into quartz, where quartz exhibits crystallographic‐preferred orientation patterns and microstructures indicative of dynamic recrystallization during dislocation creep. Grain size reduction during dynamic recrystallization led to the onset of grain boundary sliding (GBS) accommodated by fluid‐assisted grain size‐sensitive (GSS) creep, localizing strain in quartz‐rich layers prior to pseudotachylyte development. The foliation‐parallel zones of GBS in the host mylonites, and the presence of GBS traits in polycrystalline quartz survivor clasts indicate that GBS zones were the ductile precursors to in situ pseudotachylyte generation. During pseudotachylyte development, strain was partitioned into the melt phase, and GSS deformation in the survivor clasts continued until crystallization of melt impeded flow, inducing pseudotachylyte development in other GBS zones. We interpret the coeval pseudotachylytes with ductile precursors as evidence of seismic events near the BDT. Grain size piezometry yields high differential stresses in both host mylonites (~160 MPa) and pseudotachylyte survivor clasts (> ~200 MPa), consistent with high stresses during interseismic and coseismic phases of the earthquake cycle, respectively.

Microstructural and rheological evolution of calcite mylonites during shear zone thinning: Constraints from the Mount Irene shear zone, Fiordland, New Zealand

Layers of calc-mylonite in the Mount Irene shear zone, Fiordland, New Zealand, show substantial variations in thickness due to deflection of the shear zone boundaries around wall rock asperities. In relatively thick parts (c. 2.6 m) of the shear zone, calcite porphyroclasts are internally strained, contain abundant subgrain boundaries and have a strong shape preferred orientation (SPO) and crystallographic preferred orientation (CPO), suggesting that deformation occurred mainly by dislocation creep involving subgrain-rotation recrystallization. In relatively thin parts (c. 1.5 m) of the shear zone, aggregates of fine-grained recrystallized calcite surrounding flattened porphyroclasts have a weak SPO and CPO, and contain polygonal calcite grains with low degrees of internal misorientation. The recrystallized aggregates also contain microstructures (e.g. grain quadruple junctions, randomized misorientation axes) similar to those reported for neighbor-switching processes during grain-boundary sliding. Comparison of subgrain sizes in the porphyroclasts to published grain-size differential-stress relationships indicates that stresses and strain rates were substantially higher in relatively thin parts of the shear zone. The primary microstructural response to higher stresses and strain rates was an increase in the amount of recrystallization to produce aggregates that deformed by grain-boundary sliding. However, even after the development of interconnected networks of recrystallized grains, dislocation creep by subgrain-rotation recrystallization continued to occur within porphyroclasts. This behavior suggests that the bulk rheology of shear zones undergoing thinning and thickening can be controlled by concomitant grain-size insensitive and grain-size sensitive mechanisms. Overall, our observations show that shear zone thickness variations at constant P-T can result in highly variable stresses and strain rates, which in turn modifies microstructure, deformation mechanism and shear zone rheology.

Experimental Investigation and Modeling of the Viscosity of Oxide Slag Systems

Numerous technical applications in the energy and metallurgical industries demand a fundamental knowledge of the flow of slags. Besides temperature and composition, which determine the internal structure of an oxide melt, crystallization in the slag significantly influences its flow behavior. Therefore, not only the temperature-dependent viscosity of fully liquid oxide melts was determined using a rotational high-temperature viscometer but also isothermal viscosity measurements were conducted, in order to examine the rheological evolution over time caused by crystallization. The crystallization behavior during flow can be separated into three time regimes: a lag-time, in which the undercooled melt behaves as an Arrhenius liquid; the kinetic-driven crystallization; and, finally, the rheological equilibrium that is represented by a time-invariant viscosity plateau. To model the viscosity of oxide slags, in a first step, a self-consistent thermodynamic database for the system SiO2–Al2O3–CaO–MgO–FeO x –K2O–Na2O–P2O5–SO x has been established. The Gibbs energy of the liquid phase has been modeled using a non-ideal associate solution description. In a second step, an Arrhenius-type model for the calculation of viscosities of fully molten slags has been developed. The model is based on the same structural units, i.e., the associates, as the one for the Gibbs energy of the melt. In a third step, the influence of crystallization, which not only transforms the liquid into dispersion but also usually changes the composition of the residual liquid, on the viscosity is considered.

Temporal Variation in Single-Cell Power-Law Rheology Spans the Ensemble Variation of Cell Population

Changes in the cytoskeletal organization within cells can be characterized by large spatial and temporal variations in rheological properties of the cell (e.g., the complex shear modulus G∗). Although the ensemble variation in G∗ of single cells has been elucidated, the detailed temporal variation of G∗ remains unknown. In this study, we investigated how the rheological properties of individual fibroblast cells change under a spatially confined environment in which the cell translational motion is highly restricted and the whole cell shape remains unchanged. The temporal evolution of single-cell rheology was probed at the same measurement location within the cell, using atomic force microscopy-based oscillatory deformation. The measurements reveal that the temporal variation in the power-law rheology of cells is quantitatively consistent with the ensemble variation, indicating that the cell system satisfies an ergodic hypothesis in which the temporal statistics are identical to the ensemble statistics. The autocorrelation of G∗ implies that the cell mechanical state evolves in the ensemble of possible states with a characteristic timescale.

Mechanical and microstructural changes of cheese cracker dough during baking

Baked food snacks constitute an important market as a popular consumer product. The mechanical properties of cheese cracker dough at different stages of baking have been investigated as they can relate to the product's texture. The change in mechanical properties during baking was measured whilst the corresponding changes in microstructure were recorded using cryo-SEM at several interrupted baking conditions. The initial modulus of the dough increased with baking time due to starch melting or gelatinisation, melting of fat globules and evaporation of water. Simultaneously gas cells were found to begin forming. The data derived from the uniaxial compression, tension and shear experiments showed that the dough exhibited a rate dependent behaviour at all stages of baking with a power law index of approximately 0.2. Rheometric tests under dynamic heating conditions were also performed and it was found that the modulus decreased significantly, from 150 kPa to 10 kPa, with the initial rise in temperature. This study provides useful data for understanding the evolution of microstructure and rheology during the baking process and its impact on the texture of the final product.

Rheological and Structural Evolution of Rubberized Asphalts under Weathering

AbstractRubberized asphalt has been widely used for extending the service life of pavement. Understanding the weathering mechanism of rubberized asphalt is useful for selecting appropriate rubberiz...

The rheological evolution of the 2014/2015 eruption at Holuhraun, central Iceland

In the period from August 29, 2014, to February 27, 2015, the largest basaltic eruption of the last 200 years in Iceland occurred within the tectonic fissure swarm between the Barðarbunga-Veiðivotn and the Askja volcanic systems. The eruption took place in the Holuhraun lava field, 45 km northeast of the Barðarbunga volcano and 20 km south of the Askja volcano. It emplaced over 1.2 km3 dense rock equivalent (DRE) of lava in an area of very low topographic relief. In light of the minimal topographic forcing, lava flow emplacement can be viewed as having been effectively controlled by the lava’s temperature-dependent rheology. Here we combine field and remote sensing data collected during the week of the 17th to 22nd of November 2014 to constrain the lava’s flow path, its velocity, deformation rate and thermal evolution during emplacement. We combine these with measurements of the pure liquid viscosity and the sub-liquidus rheological evolution of the lava during crystallization. Sub-liquidus experiments were performed at a range of constant cooling and shear rates, to mimic the conditions experienced by the lava during emplacement. These data can also be used to infer flow conditions of partly degassed magma within dike-swarms during transport towards the surface. The data show that the effective viscosity of the lava drastically increases until reaching a specific sub-liquidus temperature, the “rheological cutoff temperature” (T cutoff). This departure to high viscosity is a consequence of the onset of crystallization and is found to be primarily controlled by the imposed cooling rate. Our data indicate that shear rate exerts a second-order effect on this rheological departure and T cutoff. We discuss the experimental dataset in the context of the reconstructions of the natural emplacement conditions and describe the implications for the 2014–2015 lava flow field at Holuhraun as well as lava flow modelling in general.