Variations In Rheological Properties Research Articles

Rheological characterization and modeling of ultra-high-velocity fluidized submarine landslides

Submarine landslides are critical phenomena due to their potential to reshape seabed topography, trigger tsunamis, and compromise offshore infrastructure. Understanding the rheological properties, particularly shear stress and viscosity under high shear rates, is essential for comprehending the dynamics of these landslides, a topic often underexplored in previous research. This study explores the rheological behavior of fluidized submarine landslides, with a focus on in-site sediments from the South China Sea and the Western Pacific Ocean. Samples prepared with varying densities were subjected to extensive rheological testing in the laboratory and analyzed under shear rates of up to 2000 s−1. Results indicated that all samples exhibited non-Newtonian fluid characteristics, showing shear-thinning behavior at low shear rates and shear-thickening behavior at higher shear rates. This transition is attributed to the breakdown of internal sediment structures, leading to changes in viscosity. This study also found that higher water content generally results in lower yield stress and consistency coefficients, while increasing the shear rate reduces the nonlinearity of the fluid's behavior. To model this complex behavior, a piecewise rheological model based on the Herschel-Bulkley framework was proposed. This model effectively captures the variations in rheological properties across different shear rate stages, with critical shear rates influenced by the sediment type and water content. These findings contribute to a deeper understanding of submarine landslides under extreme conditions, and the proposed model offers a more accurate tool for predicting the behavior of fluidized submarine landslides.

Variations of Rheological Properties and Wall Slip of Polyethylene in Nanoconfined Channels Studied by MD Simulation

Variations of Rheological Properties and Wall Slip of Polyethylene in Nanoconfined Channels Studied by MD Simulation

On diagnostics of the properties of functional-gradient composites considering rheology

Abstract The solution of inverse problems on determining the variable rheological properties of functional-gradient beams using additional information about the angle of rotation of the end section is presented within the framework of the most used models: Euler–Bernoulli and Timoshenko. Within the framework of the concept of complex modules, nonlinear operator equations are obtained that connect the given and sought functions (instantaneous and long-term module, relaxation time). The solution is based on the linearization method and the formulation of an iterative process, at each step of which it is necessary to solve complex-valued boundary value problems and invert completely continuous operators with complex-valued kernels. Functions reflecting the laws of change in long-term and instantaneous modules have been restored. The results of computational experiments in some special cases are presented.

Effects of Aging on Rheological Properties and Microstructural Evolution of SBS Modified Asphalt and Crumb Rubber Modified Asphalt Binders

Focusing on the comparison of aging resistance between styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) and crumb rubber modified asphalt binders (CRMA), the influences of aging on rheological properties and microstructural characteristics of different modified asphalts were investigated in this work. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were carried out, and the variations in rheological properties for different modified asphalts after the rotating thin film oven test (RTFOT) were analyzed with the rutting factor aging index (RAI) and creep rate aging index (CAI). By using Fluorescence microscopy (FM) and Fourier transform infrared (FTIR) spectroscopy, the evolutions of microstructure and chemical composition for two modified asphalts were analyzed with carbonyl index growth rate (CIR) and sulfoxide index growth rate (SIR). Then, The relationships between CIR/SIR and RAI/CAI were established to show the correlation between the deterioration of macroscopic performance and the evolution of micro-structure. The results indicated that the aging degree of asphalt increases with elevated temperatures, leading to decreasing low-temperature performance while improving high-temperature performance. Nevertheless, SBSMA exhibited strong sensitivity to aging temperature. Under thermo-oxidative aging, the RAI and CAI of SBSMA were lower than those of CRMA, whereas the regularities of CIR and SIR were opposite, indicating that CRMA was superior to SBSMA in terms of anti-aging properties due to the rupture of the cross-linked network structure of SBSMA. However, CRMA experienced aging accompanied by full swelling, and thus, relatively minor performance declined. The CIR and SIR exhibited a better correlation with the RAI and CAI, illustrating that both CIR and SIR could characterize the aging degree of modified asphalts well.

Investigating the impact of exopolysaccharides on yogurt network mechanics and syneresis through quantitative microstructural analysis

Exopolysaccharides produced by lactic acid bacteria are widely used to improve the sensory properties of yogurt. The relation between the physical properties of the microbial exopolysaccharides and the structural and rheological properties of the yogurt are incompletely understood to date. To address this knowledge gap, we studied how two distinct exopolysaccharides influence the microstructure, rheological properties, and syneresis of yogurt. The effect of a negatively charged, capsular exopolysaccharide produced by Streptococcus thermophilus and a neutral, non-capsular exopolysaccharide produced by Lactococcus lactis were investigated. Using quantitative microstructural analysis, we examined yogurt samples prepared with either the capsular or the non-capsular exopolysaccharide, and with mixtures of the two. Confocal laser scanning microscopy and stimulated emission depletion microscopy were employed to visualize the microstructures, revealing differences in pore size distribution, protein domain size, and casein interconnectivity that were not apparent through visual inspection alone. Additionally, variations in rheological properties were observed among the different yogurt types. In the yogurt fermented with both bacterial strains, we observed a combined impact of the two exopolysaccharide types on relevant microstructural and rheological properties. The negatively charged capsular exopolysaccharide enhanced casein interconnectivity and gel stiffness, while the neutral non-capsular exopolysaccharide led to thicker protein domains, an abundance of small pores, and a lower loss tangent. These factors collectively hindered syneresis, resulting in improved structural integrity. Our study not only provides valuable insights into the influence of different exopolysaccharides on yogurt properties, but also presents the first demonstration and quantification of the effect of multiple types of exopolysaccharides on casein interconnectivity. These findings offer guidance for the production of yogurts with customized microstructure, rheological properties, and resistance to syneresis.

Rheology‐cell structure correlation for foam processing of polypropylene‐titanium dioxide and polypropylene‐graphene nanocomposites

AbstractThis work focuses on understanding the effects of nanoparticle fillers (titanium dioxide (TiO2) and graphene) on foam processing of polypropylene(PP) and makes an attempt to establish a rheology‐cell size correlation for PP‐TiO2 and PP‐graphene nanocomposite foams. The establishment of such a correlation can help develop a precise model to predict optimum nanoparticle concentration in a polymer matrix to produce stable microcellular foams. The effects of adding TiO2 and graphene nanoparticles on nanocomposite properties are studied through their thermal, mechanical, and rheological analysis. The nanocomposite/PP foams are prepared at various conditions, and their morphology and density are studied to obtain an understanding of the cell structure as a function of added nanoparticles. The optimized size/structure has also been correlated in terms of rheological and mechanical properties of the prepared nanocomposites to study the effects of variation in rheological properties on the resultant cell structure of prepared foams. Through the current work it was found that particle type/size plays the dominant factor in determining the cell size of resultant foam, although when comparing foams with varying filler concentration, it was established that a decrease in viscosity and storage modulus would create more cell stability by decreasing the applied stress and would lead to smaller cells.Highlights Rheological property variation can directly affect the polymer foamability Foaming of polymers can be closely simulated using the Maxwell model for polymers Reduction in viscosity leads to smaller and stable cells during foaming Stress relaxation rate determines the cell stabilization during expansion Agglomerate size plays a crucial role in determining cell size

Исследование коэффициентных обратных задач с учетом реологии для функционально-градиентных стержней

The problems of determining the variable rheological properties of functionally gradient beams from some additional information about displacements are considered. Vibrations of a cantilevered inhomogeneous viscoelastic beam are studied in the framework of two models - Euler-Bernoulli and Timoshenko. The oscillations are caused by a moment concentrated at the end of the beam, oscillating in time. Within the framework of the concept of complex modules, operator relations linking the given and desired functions are obtained. Functions reflecting the laws of change of long-term and instantaneous modules have been restored. The results of computational experiments on the restoration of functions of various types are presented.

The Effect of Fiber Volume Fraction on Fiber Distribution in Steel Fiber Reinforced Self-Compacting Concrete

This paper investigates the effect of fiber volume fraction on fiber distribution in steel fiber reinforced self-compacting concrete (SFRSCC) through experiments and numerical simulations. Three types of SFRSCC beam specimens with different fiber volume fractions (0.3%, 0.6%, and 0.9%) were cut to expose the steel fibers. The number and the orientation angle of the steel fibers on the beam sections were determined by image analysis techniques. Fiber density, fiber segregation coefficient, fiber dispersion coefficient and fiber orientation coefficient were applied to evaluate fiber distribution on the beam sections. Based on the experimental data, numerical models simulating the pouring process of fresh SFRSCC were established to analyze the overall fiber distribution in the specimens. The results show that the distribution state of the fibers on the beam sections is not random and uniform, which is correlated to the fiber volume fraction. Due to the variable rheological properties, a greater fiber volume fraction causes better fiber uniformity, lower fiber segregation and worse fiber alignment on the beam sections. Meanwhile, the numerical results show that the distribution law of fibers along the length direction of the specimens is almost independent of the fiber volume fraction. In addition, increasing the fiber volume fraction results in the increase of the average angle of the fiber orientation in the specimens. The results can provide a reference for optimizing the fiber distribution in the concrete matrix.

Shear thickening in dense bidisperse suspensions

Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from δ=1.4 (nearly monodisperse) to δ=4, and the large particle fraction of the total solid loading with values ζ=0.15, 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction ϕJ with shear stress σ are reported. At a fixed volume fraction ϕ, bidispersity decreases the suspension relative viscosity ηr=ηs/η0, where ηs is the suspension viscosity and η0 is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at ζ≈0.5, but instead decreases with further increase of ζ to 0.85. The second normal stress difference N2 acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosity ηr of bidisperse rate-dependent suspensions can be predicted by a power law linking it to ϕJ, ηr=(1−ϕ/ϕJ)−2 in both low and high shear stress regimes. The agreement between the power law and experimental data from literature demonstrates that the model captures well the effect of particle size distribution, showing that viscosity roughly collapses onto a single master curve when plotted against the reduced volume fraction ϕ/ϕJ.

Thermal, mechanical, rheological and morphological properties of compatible poly(lactic acid)/ethylene vinyl acetate blends

This paper examines the effects of poly (ethylene-co-vinyl acetate) (EVA) with 40% vinyl acetate content on thermal, mechanical, rheological, and morphological properties of polylactic acid (PLA) blends. Thermal analysis indicated improvement of crystallinity in the presence of more EVA. With 15% EVA, the impact strength of the binary blend increased significantly (37.80 KJ/m2) at an optimum elongation at break due to the compatibility of the blend and the formation of fibrils. In the presence of % EVA, complete phase separation with the formation of EVA droplets in the PLA continuous phase resulted in a reduction of impact strength and elongation at break. Changes in compatibility and morphology lead to variation in rheological properties. The complex viscosity (η*) decreased with increasing EVA content up to 10% EVA but slightly increased at 15% EVA due to optimum interphase interaction between components in the compatible blend. In the presence of more than 20% EVA, η* reduced again due to the occurrence of phase separation. The variations in the mechanical and rheological properties of PLA/EVA blends are directly related to the state of compatibility and morphology of the blends.

Understanding Robustness of Magnetically Driven Helical Propulsion in Viscous Fluids Using Sensitivity Analysis

AbstractMagnetically‐actuated helical microrobots can propel themselves in fluids and tissues‐like mediums with a wide range of Reynolds numbers (Re). The properties of physiological fluids and input parameters vary in time and space and have a direct influence on their locomotion along prescribed paths. Therefore, understanding the response of microrobots to variations in rheological properties and input parameters become increasingly important to translate them into in vivo applications. Here, a physical framework is presented to understand and predict key parameters whose uncertainty affect certain state variables most. A six‐degree‐of‐freedom magneto‐hydrodynamic model is developed based on the resistive force theory (RFT) to predict the response of robots swimming through different fluids and examine their response during transitions into Newtonian–viscoelastic interfaces. Performance of the robot, while swimming in a fluid with a fixed viscosity, is quantified using sensitivity analysis based on the magneto‐hydrodynamic model. The numerical results show how abrupt changes in viscosity can affect their ability to rotate with the rotating field in synchrony. The sensitivity analysis shows that the states of the robot are mostly sensitive to variations in the actuation frequency. Open‐loop experiments are performed using a permanent‐magnet robotic system comprising a robotic arm and a rotating permanent magnet to actuate and control a helical robot at the Newtonian–Viscoelastic interface and validate the theoretical predictions of the RFT‐based sensitivity analysis.

Preparation and experimental research on the properties of neodymium iron boron magnetic powder modified asphalt

Waterproof adhesive layer is an important part of the asphalt pavement system for steel bridge decks. To improve the strength and durability of the paving structure, it is necessary to focus on the high-temperature performance and bonding properties of the waterproof adhesive layer. In this paper, Neodymium iron boron magnetic powder (NP) mixed with SBS modified asphalt was used to prepare NP-SBS composite modified asphalt (NSA) for the waterproof adhesive layer material of the steel bridge deck pavement structure. The excellent mechanical and magnetic properties of NP are used to enhance the related properties of the waterproof adhesive layer. The dynamic shear rheometer (DSR) test, the bending beam rheometer (BBR) test, the direct-tensile-loading test, and the direct-shear-loading test with 6 NP contents (0%, 2%, 4%, 6%, 8%, 10%) were conducted to evaluate the high-temperature performance, the low-temperature performance, the tensile strength and the shear strength of the unmagnetized and magnetized NSA. Through these tests, the variation of rheological properties and bonding properties of NSA could be analyzed. The research results showed that the addition of NP improved the high-temperature performance of NSA, but the effect of the powder mortar had an adverse effect on the low-temperature performance. The tensile strength and shear strength of the NSA increased with the increase of the amount of NP, and the amount of 1.0 L/m2 and the NP content of 6% can achieve better bonding properties. After magnetization, the high-temperature performance and bonding properties of NSA will be further improved, but the low-temperature performance will also be further decreased. It reflects the effect of NP on powder modification, magnetic bonding, and magnetic hardening of NSA. The research results show that NSA has excellent high-temperature performance and bonding properties, which can provide a reference for the subsequent research and application of NSA.

Contrasting Response of West and East Antarctic Ice Sheets to Glacial Isostatic Adjustment

AbstractThe Antarctic ice sheet (AIS) lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low‐viscosity upper mantle (weak Earth structure) beneath West Antarctica and an opposing structure beneath East Antarctica. This contrast is known to have a significant impact on the ice‐sheet grounding‐line stability. Here, we embed within an ice‐sheet model a modified glacial‐isostatic Elastic Lithosphere‐Relaxing Asthenosphere model that considers a dual pattern for the Earth structure beneath West and East Antarctica supplemented with an approximation of gravitationally consistent geoid changes, allowing to approximate near‐field relative sea‐level changes. We show that this elementary GIA model captures the essence of global Self‐Gravitating Viscoelastic solid‐Earth Models (SGVEMs) and compares well with both SGVEM outputs and geodetic observations, allowing to capture the essential features and processes influencing Antarctic grounding‐line stability in a computationally efficient way. In this framework, we perform a probabilistic assessment of the impact of uncertainties in solid‐Earth rheological properties on the response of the AIS to future warming. Results show that on multicentennial‐to‐millennial timescales, spatial variability in solid‐Earth deformation plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high‐emissions climate scenarios. On longer timescales and for unmitigated climate scenarios, continent‐wide mass loss projections may be underestimated because spatially uniform Earth models, as typically considered in numerical ice sheet models, will overestimate the stabilizing effect of GIA across East Antarctica, which is characterized by thick lithosphere and high upper‐mantle viscosity.

Effect of temperature variation on the accurate prediction of bottom-hole pressure in well drilling

ABSTRACT Knowing the effects of different parameters on the drilling fluid is an essential part of a successful and safe drilling operation. High pressure and high temperature conditions have opposing effects on the fluid density which has an important effect on the bottom-hole pressure. So for estimating precise bottom-hole pressure, it is essential to take into account these opposite effects on drilling fluid compression or expansion. In this study, Bingham-plastic model is considered as drilling fluid to simulate drilling operation and develop temperature and pressure distribution through the wellbore. The effects of variation in drilling fluid flow rate, drilling fluid specific heat and inlet mud temperature are explored and discussed for an oil-based mud. Also, the effects of frictional pressure loss, pressure loss in the drill bit and, drill string rotation are considered as internal heat sources in the wellbore. Results show that thermal interaction is required for accurate prediction of the bottom-hole pressure. Variations of different parameters change temperature distribution in the wellbore which consequently changes the bottom-hole pressure. The results show that considering the variation of rheological properties, bottom-hole pressure prediction may change as much as 685 psi (about 2.30%) which is considerable. Model predictions were compared with the field data for validation of the model.

Experimental and Numerical Studies of a Soft Impact Piezoelectric Energy Harvesting Using an MR Fluid

Numerical and an experimental study of a soft impact-based piezoelectric energy harvesting system employing a thin layer of magnetorheological (MR) fluid as the impact object is presented in this paper. MR fluid devices are mostly used as vibration suppressors in automobiles and other machinery. MR fluids exhibit variable rheological properties in the presence of a magnetic field, which makes them excellent vibration attenuation devices with easily adaptable damping forces. This behavior can be exploited in vibration energy harvesting to aid frequency up-conversion. The study is carried by solving the theoretical equations numerically and then validating the results experimentally. The Heaviside function is used to model the piecewise nonlinear dynamics of the proposed system. In this way, the sticky and inelastic behavior of the fluid, which causes a time-delay in the oscillations of the beam is best described. The results obtained indicated that increasing the magnetic field increases the voltage generated through frequency amplification. The voltage obtained with a load resistance of 200 k $\Omega $ increased from 9.29 V to 9.42 V when the magnetic field increases from 0.04T to 0.08T for the numerical study and 7.71 V to 8.46 V when the field increased from 0.044T to 0.085T in the experimental study. The frequency is amplified from 59.58 Hz at 0.04T to 82.76 Hz at 0.08T for the numerical results and from 61.02 Hz at 0.044T to 83.04 at 0.085T for the experimental results. The MR fluid acts as a soft impact object in this work.

Micro-mechanism analysis of the rheological properties of water-in-waxy-crude-oil emulsion under pipe flow

Flowing experiments with different water contents in water-in-waxy-crude-oil emulsions were performed in a flow loop apparatus. The real-time variations of rheological properties and microscopic distributions of the emulsions over time during pipe flow were quantitatively analyzed. It was found that the emulsification effect of the emulsion is enhanced due to shear effect, resulting in an increase of gel point and viscosity over time. The average increments in the gel point are approximately 1.5 °C, 1.7 °C and 1.9 °C for the emulsions with water contents of 10%, 20% and 30%, respectively. During the experimental period from 0.5 h to 18 h, the average viscosities measured at the emulsion temperature increase by 31%. Characterization parameters of number-averaged diameter (d 1,0), specific surface area (SA) and polydispersity (PDI) were applied to reflect the microstructure of emulsions from the perspectives of droplet size, dispersity and nonuniformity. The water droplets become smaller and uniformly dispersed as the pipe flow goes on. The Gibbs free energy increases as the emulsion flows through the pipe, which is mainly caused by the shear of the pipe wall. The van der Waals force increases from −0.0678 × 10−21 J to −1.7657 × 10−21 J as the emulsion’s water content changes from 10% to 30%. The water droplets can promote crystallization of wax crystals by offering the necessary nucleus surface. Furthermore, the coexistence of water droplets and wax crystals creates a synergistic effect, which can augment the total energy and structural strength of the emulsion system.

Insight into the response of anammox granule rheological intensity and size evolution to decreasing temperature and influent substrate concentration

Anammox granules are advantageous because of their relatively higher nitrogen removal rate (NRR) and biomass retention capacity in ammonia-containing wastewater treatment. However, little attention has been paid to granule rheological intensity and size evolution, especially under low temperature and substrate concentration conditions. In this study, the size evolution and variations in rheological properties associated with biochemical characteristics of anammox granules were investigated at decreasing temperatures (35 → 13 °C) and influent substrate concentrations (300 → 50 mg NH4+-N L−1). Both the specific anammox activities (SAA) and yield stress (τc) (or storage modulus (G′)), which reflected granules' intensity, decreased with decreasing temperature and influent substrate concentration. An exponential correlation was found between SAA and τc (or G′). Granule size strongly decreased at low temperature (13 °C) and influent substrate concentration (50 mg NH4+-N L−1), despite slight variations in τc (or G′). A threshold τc (or G′) that is closely related to the hydrodynamic shear force in the reactor may exist for the anammox granules. Once the τc (or G′) of the anammox granules was lower than this threshold value (τc∗ = 10.13–15.63 kPa), granules that could not endure hydrodynamic shear forces would disintegrate and their size would decrease substantially. Candidatus Kuenenia was the dominant genus in the expanded granular sludge bed reactor, reaching a minimum abundance of 14.6% at 16 °C because of the low-temperature shock, but increasing in abundance to 57.0% at 13 °C, indicating it has a competitive advantage at low temperatures. This contributed to achieving a high reactor nitrogen loading rate (>1.0 kg N m−3 d−1) even at 13 °C or with 50 mg NH4+-N L−1 influent. Overall, the results of this study will facilitate management of anammox bioreactors that run at various temperatures and influent substrate concentrations by clarifying the correlation between rheological intensity and anammox granule sludge activity and identifying the τc (or G’) threshold.

Influence of Poker Vibration on Aggregate Settlement in Fresh Concrete with Variable Rheological Properties

AbstractInternal vibration is adopted worldwide for consolidating fresh concretes in field construction. Improper manual operation of the vibration process can easily induce segregation and bleedin...

Simulating yield stress variation along hydraulic fracture face enhances polymer cleanup modeling in tight gas reservoirs

Several measures have been taken to enhance the supply of fossil fuel energy in the United States during the last decades, some of which include the development and exploitation of very low permeability and low porosity reservoirs in challenging environments. These reservoirs usually require enhanced stimulation techniques such as multi-stage hydraulic fracturing and horizontal drilling to increase the contact between the wellbore and the producing formation for a profitable recovery. During the fracturing process, fluids are pumped into the reservoir under high pressure, to create fractures through which gas flows back to the earth's surface during production. However, a layer of concentrated polymer forms on the fracture faces limiting the loss of fluid to the formation during injection while impairing fracture conductivity during production. The inadequacy of the fracture conductivity after a fracture treatment using cross-linked fluids is typically due to poor degradability of our polymers, proppant crushing, clay swelling in the case of incompatible fluids and formation damage. The objective of this work is to develop a fracture cleanup model that simulates the rheological variations of filter cake and degraded fluids inside the fracture by including the effect of breaker and polymer concentration on the yield stress of the fracturing fluid that result in variations in capillary pressure, fracture conductivity, fracture length and formation damage during the cleanup process in unconventional tight gas formations.A dynamic 2-D, three-phase IMPES simulator, incorporating a yield-power-law-rheology (Herschel-Buckley fluids), has been developed in MATLAB to simulate variations in rheological properties of degrading fracturing fluids versus time and investigate the influence of several major parameters on the fracture cleanup process. These parameters include variations in polymer concentration along the fracture length, breaker concentration variations, fracture conductivity, fracture length, capillary pressure and formation damage with a novel correlation between yield stress and breaker concentration, which enhances post – fracture well performance prediction in tight gas reservoirs. The three phases simulated here include water, gas and the gel phases.Simulation of the injection of fracturing fluids and fluid imbibition during the shut-in time indicated that for tight gas formations, fluid recovery increases with increasing shut-in time, increasing fracture conductivity and fracture length irrespective of the yield stress of the fracturing fluid. Simulation of the production phase highlighted that increasing the capillary pressure to a maximum of 350.10 psi resulted in a 10.4% decrease in cumulative gas production. The rate of increase in the yield stress of the fracturing fluid along the fracture face is proportional to the square of the volume of fluid loss to the formation. Production will be enhanced significantly with increasing breaker concentration indicating that simulation of the yield stress variation along the fracture face presents a more realistic scenario of the fracture cleanup process rather than assuming a constant value since the fluid loss to the formation and the polymer concentration distribution decrease with fracture length.

Elastohydrodynamic lubricant flow with nanoparticle tracking.

Lubricants operating in elastohydrodynamic (EHD) contacts exhibit local variations in rheological properties when the contact pressure rises. Direct evidence of this behaviour has only been obtained by examining through-thickness velocity profiles U(z) of lubricants in a contact using luminescence-based imaging velocimetry. In the present study, nanoparticles (NPs) are added to polybutene (PB) as tracers to investigate the effect of pressure on the flow of PB in an EHD contact. By tracking NPs in the contact, particle velocity distributions f(U) under various pressures are obtained and found to be pressure dependent. Results show quantitatively that f(U) and U(z) are correlated and thus confirm that U(z) of PB changes from Couette flow to partial plug flow above a critical pressure. This confirmation highlights the complexity of lubricant rheology in a high pressure contact.