Stress Fluctuations Research Articles

Lycopene attenuates oxidative stress, apoptosis, and biochemical fluctuations induced by bisphenol A in the kidney of rats

Lycopene attenuates oxidative stress, apoptosis, and biochemical fluctuations induced by bisphenol A in the kidney of rats

STUDY OF LOW-TEMPERATURE THERMOMECHANICAL BEHAVIOR OF THE Ti-18Zr-15Nb SUPERELASTIC ALLOY UNDER DIFFERENT TEMPERATURE-RATE CONDITIONS

The biomedical alloy Ti-18Zr-15Nb (at.%) with shape memory was subjected to a true deformation e = 0.7 in three different modes: in the temperature range from 20°C to 600°C at deformation rate ξ = 0. 1 s-1; at temperatures 250°C and 300°C with strain rates ξ = 0.1, 1 and 10 s-1; deformation at 300°C and strain rate ξ = 0.1 s-1 after annealing at 300°C (τ = 10, 60, 300, 600 and 1200 s). It is established that with increasing temperature the conditional yield strength σ0.2 continuously decreases, at that in the temperature range of deformation temperatures 250°С-300°С the increase of maximum stress σmax is observed. In the temperature range from 200°С to 400°С fluctuations are observed on the flow curves, the amplitude of which increases with increasing temperature. The change σ0.2 and σmax, as well as the presence of oscillations on the strain diagrams are connected with the course of dynamic strain aging accompanied by the release of excess ω-phase particles at temperatures 200°С - 400°С. Increasing the strain rate at temperatures of 250°С - 300°С has a strong effect on the deformation behavior of the alloy due to a significant increase in temperature during the deformation process. Thus, increasing the strain rate up to ξ = 10 s-1 leads to a stepwise decrease in stress, starting from e ≈ 0.3, after which the plastic flow curve acquires a wave-like form with a low frequency of stress fluctuations. The main phase after all modes of thermomechanical tests is the BCC β-phase. At annealing of 300°С and an exposure of more than 300 s weak ω-phase lines are observed, and at deformation after aging significantly broadened ω-phase lines are observed only after prolonged exposure (1200 s).

Effect of heat treatment on mechanical properties, failure modes and energy absorption characteristics of lattice skeleton and sheet structures fabricated by SLM

Triply periodical minimal surface (TPMS) structures have attracted much attention in the biomaterials, aerospace, and automotive industries because they are lightweight, have high strength, and can absorb energy and shocks. In this study, uniform skeletal (USK), uniform sheet (USH), grade skeletal (GSK), and grade sheet (GSH) diamond lattice structures with the same 20% volume fraction were fabricated by selective laser melting (SLM) using AlSi10Mg metal powder. Their mechanical properties, deformation behavior, and energy absorption performance were systematically investigated by compression tests and finite element analysis (FEA). The skeleton structures had a higher elastic modulus, yield strength, and more severe stress fluctuation than the sheet structures. In addition, comparing the 45° shear deformation for as-built uniform structures accompanied by a mixture of ductile and brittle fracture modes, both gradient structures fractured by a sub-layer pattern from the layer with a lower volume fraction. Furthermore, the numerical simulation results illustrated that the stress of the skeleton structures was mainly concentrated at the skeleton joint, while the sheet structures were distributed evenly on the thin wall, without being concentrated in the interconnection region. For skeleton structures, heat treatment controlled the failure degree by improving the microstructure of the material, while for GSH structures at 300 °C, the fracture mode changed from the previous layer-by-layer fracture to a 45° shear failure. The accumulated energy absorption of gradient structures was more than that of the uniform structure, especially the GSH structures and the energy absorption efficiency of the skeleton structures was higher.

Strengthening mechanism and plasticity deformation of crystalline/amorphous Cu3Fe/Fe3Cu nanolayered composite

Metallic glasses possess high strength and excellent elastic properties due to their amorphous atomic structure. However, they often display brittleness and suffer catastrophic failure because of shear localization, without exhibiting significant macroscopic plastic deformation under tension. In this paper, an effective method to enhance the strength and ductility of metallic glasses is presented by molecular dynamics simulation. The approach involves controlling the thickness of the crystalline Cu3Fe and amorphous Fe3Cu layers. The results indicate that increasing the thickness of the crystal layer improves the strength of the nanolayered composite. The crystalline/amorphous interface impedes stress propagation in the shear transformation zone, thereby enhancing the yield stress of the composite. Additionally, the presence of Hirth dislocations in the crystal layer strengthens the composite. The generation and annihilation of fixed dislocations in the crystal layer cause stress fluctuations in the composite, which further enhances its ductility. However, a small content of crystalline layer can cause stress concentration towards the shear band, leading to rapid fracture failure and reduced ductility. These findings shed light on the plastic deformation behavior of crystalline/amorphous composites at the nanoscale, providing valuable theoretical guidance for designing high-strength and ductile metallic materials.

Model test on thermo-mechanical properties of static drill rooted energy pile under long-term temperature cycles

Static drill rooted (SDR) pile emerges as a composite of a prefabricated pile and cemented soil. SDR pile technology was introduced into the energy pile design due to its high load-bearing capacity, excellent heat transfer performance and favorable stability. Indoor model tests were established to investigate the thermo-mechanical behavior of an SDR energy pile under long-term temperature cycles. It was found that the studied pile had better heat transfer performance and bearing capacity (50%) than the ordinary pile. After twenty long-term temperature cycles, Additional tensile and compressive stress were observed in the pile. The additional thermal stress in the pile initially increased and then decreased with the increasing depth of the pile. The stress fluctuation would not damage the pile material since it was maintained within the design value of concrete strength. The side friction of the pile gradually increased with the increasing cycle numbers. The cumulative settlement of the SDR energy pile was induced by temperature cycles and reached −0.155 mm (0.18% D) after 20 cycles, less than the ordinary pile. The first two cycles accounted for 53% of the total cumulative settlement, and cooling was the main factor causing pile top settlement. The ultimate bearing capacity of the SDR energy pile was decreased by 9% after 20 cycles. The investigation of the long-term thermo-mechanical behavior of the SDR energy pile provides a theoretical basis for its practical application. SDR energy piles are significant for the efficient use of shallow geothermal energy.

Influence of Non-Newtonian Viscosity on Flow Structures and Wall Deformation in Compliant Serpentine Microchannels: A Numerical Study.

The viscosity of fluid plays a major role in the flow dynamics of microchannels. Viscous drag and shear forces are the primary tractions for microfluidic fluid flow. Capillary blood vessels with a few microns diameter are impacted by the rheology of blood flowing through their conduits. Hence, regenerated capillaries should be able to withstand such impacts. Consequently, there is a need to understand the flow physics of culture media through the lumen of the substrate as it is one of the vital promoting factors for vasculogenesis under optimal shear conditions at the endothelial lining of the regenerated vessel. Simultaneously, considering the diffusive role of capillaries for ion exchange with the surrounding tissue, capillaries have been found to reorient themselves in serpentine form for modulating the flow conditions while developing sustainable shear stress. In the current study, S-shaped (S1) and delta-shaped (S2) serpentine models of capillaries were considered to evaluate the shear stress distribution and the oscillatory shear index (OSI) and relative residual time (RRT) of the derivatives throughout the channel (due to the phenomena of near-wall stress fluctuation), along with the influence of culture media rheology on wall stress parameters. The non-Newtonian power-law formulation was implemented for defining rheological viscosity of the culture media. The flow actuation of the media was considered to be sinusoidal and physiological, realizing the pulsatile blood flow behavior in the circulatory network. A distinct difference in shear stress distributions was observed in both the serpentine models. The S1 model showed higher change in shear stress in comparison to the S2 model. Furthermore, the non-Newtonian viscosity formulation was found to produce more sustainable shear stress near the serpentine walls compared to the Newtonian formulation fluid, emphasizing the influence of rheology on stress generation. Further, cell viability improved in the bending regions of serpentine channels compared to the long run section of the same channel.

Microstructure evolution of AZ80 magnesium alloy in semi-solid compression by molecular dynamics simulation

Molecular dynamics (MD) simulation and experiments were carried out in this work to probe the microstructure evolution in the semi-solid compression (SSC) of AZ80 magnesium alloy. The liquid phase flow, stress fluctuations, grain refinement, dislocation generation, and texture evolution were discussed. Results indicate that the liquid phase was squeezed out along the radial direction prior the solid phase at the beginning of compression. Stress-strain curve represented obvious fluctuation at lower strain rates. That resulted from stress reduction caused by more liquid evolving with a lower strain rate at an elevated temperature. Plastic deformation was detected in grains and the dislocations of 1/3<11¯00> dominated the deformation, while and 1/3<12¯10> just been activated at the beginning of SSC process. The results of EBSD showed the grains size was refined into about 38.8 μm from 92.3 μm after SSC process. During the process, grain refinement resulted in the increase of low-angle grain boundaries (LAGBs), and a strong (0001) basal plane texture evolved at the end. The higher the strain rates, the stronger the texture.

Prediction of the phase difference between large-scale velocity and Reynolds stress fluctuations in wall turbulence

A resolvent-based model was used to predict the phase-difference profile between velocity and stress coherent motions measured in a high Reynolds number channel flow as a proxy for predicting large- and small-scale turbulent interactions. The resolvent model is based on the transfer-function approach for scale interactions in wall turbulence proposed in Jacobiet al.(J. Fluid Mech., vol 914, 2021, pp. 1–27), but incorporates a quasi-empirical weighting scheme to construct composite mode shapes that represent the realistic dispersion of convection velocities associated with the large scales of turbulence. The weighting scheme was derived from the observed similarity between the spectral region where the resolvent operator is low rank and the streamwise spectral energy density of wall-bounded turbulence, and was found to be superior to both single-convection velocity models and models based on linearly weighted modes, when compared with cross-spectral phase calculations from a channel flow computation. The ability to predict the phase relationship between large-scale coherent motions and their associated stress fluctuations allows for refining and extending resolvent-based models of turbulence to describe small-scale features of wall-bounded flows.

Research on Dynamic Response of a Single-Tower Cable-Stayed Bridge with Successive Cable Breaks Based on a 3D Index

Aiming at the problem of cable breakage of an asymmetric single-tower cable-stayed bridge by taking a single-tower cable-stayed bridge that has been in operation for more than 20 years as an engineering example, a spatial finite element model that reflected the actual stress state of the structure was established and a method for solving the time point of cable breakage was proposed. The results show that the strength of the main girder, pylon and cable could meet the stress requirements of the vibration caused by successive cable breaks, and the maximum dynamic displacement of the main girder did not exceed the stiffness limit. Although the breakage of the stay cable caused the stress in the adjacent position and the corresponding position on the opposite side of the tower to increase sharply, the stress fluctuation in other positions was small. The fluctuation of the dynamic stress of the cable tower was relatively small, but the displacement of the tower top changed greatly. The dynamic response of the cables breaking in succession was less than that of simultaneous breaking, and the structural vibration caused by cable breaking was not as severe as that caused by simultaneous breaking.

Intraventricular Hemorrhage in Premature Infants: A Review of Risk Factors, Pathology, Treatment, and Prognosis

Abstract Intraventricular hemorrhage (IVH) in newborns is defined as bleeding within the ventricles, surrounded by the brain. This condition is most commonly observed in premature newborns and is directly proportional to gestational age; the smaller the gestational age, the higher the risk of IVH. It typically occurs in the subependymal germinal matrix, a highly vascularized area undergoing significant development in newborns and regression in full-term infants. The etiology is multifactorial and primarily attributed to the intrinsic fragility of the vascularization of the germinal matrix. Risk factors for IVH in premature infants include the immaturity of the cerebral vascular system, fluctuations in blood pressure, hypoxia, and oxidative stress. Furthermore, clinical factors such as respiratory distress syndrome, mechanical ventilation, and coagulation disorders contribute to the vulnerability of preterm infants to this complication. Regarding treatment, interventions can range from careful monitoring and medical support to surgical procedures such as cerebrospinal fluid drainage or ventriculoperitoneal shunting in severe cases. Pharmacological therapy, including the use of anti-inflammatory drugs, may be implemented to minimize brain injuries. Complications of IVH include obstructive hydrocephalus, non-obstructive hydrocephalus, post-hemorrhagic hydrocephalus, developmental disorders, cerebral palsy, and seizures. In conclusion, IVH in premature infants remains a complex and delicate issue in neonatology. An integrated approach covering both prevention and treatment is essential to minimize the negative impact of this complication on the neurological development of premature infants. Continuous research is necessary to develop innovative and effective strategies for managing this critical problem in neonatal medicine. Transfontanelar ultrasound remains the election method for diagnosis. Mild and moderate forms have shown favorable progression, while severe IVH has led to the development of post-hemorrhagic obstructive hydrocephalus.

Assessing continuum plasticity postulates with grain stress and local strain measurements in triaxially compressed sand

Critical state and continuum plasticity theories have been used in research and engineering practice in soil and rock mechanics for decades. These theories rely on postulated relationships between material stresses and strains. Some classical postulates include coaxiality between stress and strain rates, stress-dilatancy relationships, and kinematic assumptions in shear bands. Although numerical and experimental data have quantified the strains and grain kinematics in such experiments, little data quantifying grain stresses are available. Here, we report the first-known grain stress and local strain measurements in triaxial compression tests on synthetic quartz sands using synchrotron X-ray tomography and 3D X-ray diffraction. We use these data to examine the micromechanics of shear banding, with a focus on coaxiality, stress-dilatancy, and kinematics within bands. Our results indicate the following: 1) elevated deviatoric stress, strain, and stress ratios in shear bands throughout experiments; 2) coaxial principal compressive stresses and strains throughout samples; 3) significant contraction along shear bands; 4) vanishing volumetric strain but nonvanishing stress fluctuations throughout samples at all stages of deformation. Our results provide some of the first-known in situ stress and strain measurements able to aid in critically evaluating postulates employed in continuum plasticity and strain localization theories for sands.

A fluoroscopic imaging-guided computational analyses to inform internal tissue loads within fat pad of the diabetic foot during gait

To accurately predict internal tissue loads for early diagnostics of diabetic foot ulcerations, a novel data-driven computational analysis was conducted. A dedicated dual fluoroscopic system was combined with a pressure mat to simultaneously characterize foot motions and soft tissue’s material properties during gait. Finite element (FE) models of the heel pad of a diabetic patient were constructed with 3D trajectories of the calcaneus applied as boundary conditions to simulate gait events. The tensile and compressive stresses occurring in the plantar tissue were computed. Predictions of the layered tissue FE model with anatomically-accurate heel pad structures (i.e., fat and skin) were compared with those of the traditional lumped tissue (i.e., homogeneous) models. The influence of different material properties (patient-specific versus generic) on internal tissue stresses was also investigated. The results showed the peak tensile stresses in the layered tissue model were predominantly found in the skin and distributed towards the circumferential regions of the heel, while peak compressive stresses in the fat tissue-bone interface were up to 51.4% lower than those seen in the lumped models. Performing FE analyses at four different phases of walking revealed that ignorance of layered tissue structures resulted in an unphysiological increase of peak-to-peak value of stress fluctuation in the fat and skin tissue components. Thus, to produce more clinical-relevant predictions, foot FE models are suggested to include layered tissue structures of the plantar tissue for an improved estimation of internal stresses in the diabetic foot in gait.

Revealing the Intrinsic Decay of Mechanoluminescence for Achieving Ultrafast‐Response Stress Sensing

AbstractConverting mechanical energy into photon emission provides a promising route for intelligent sensing, self‐powered lighting, and distributed energy harvesting, which is of great significance for finding a feasible solution to the current sensing technical bottleneck and energy crisis. As the basis for understanding the conversion mechanism and realizing high‐frequency mechanical energy utilization, elucidating the dynamic process of intensity variation in the mechano‐to‐photon conversion remains a great challenge. Herein, a time‐domain characterization scheme that enables to unravel the intrinsic decay of mechanoluminescence (ML) with lifetimes from milliseconds down to tens of microseconds is constructed. It is demonstrated that ML decay characterization is an important tool to reveal the dynamics of charge migration in ML materials. The ML decay in a typical self‐reproducible ML material ZnS:Mn2+ shows temperature dependence and stress fluctuation resistance, which opens up a new reliable approach for self‐powered and remote temperature sensing. Finally, benefiting from the shortest ML lifetime recorded to date, an ultrafast‐response stress sensor that enables to detect individual pulses of ultrasonic waves with ML sensing technology is developed.

Microstructure reconfiguration of duplex high entropy alloy/BCC ferrite bimetallic interface under electropulsing

Additive manufacturing of multi-materials is one of the effective pathways to enrich the performance diversity of metallic materials, and it is generally acknowledged that the bimetallic interface is the weakest position because of stress concentration and compositional mutation. Here it was found that the stress concentration along the BCC + FCC duplex Al-Co-Cr-Fe-Ni high entropy alloy/BCC ferrite bimetallic interface can be significantly released by electropulsing, and the compositional mutation region was also reasonably widened from 2 μm to 10 μm. Meanwhile, the neighboring grains rotated to form High Angle Grain Boundaries, which can reduce the Gibbs free energy of the system. Additionally, the nano-scale second phase including spherical BCC NiAlFe and rod-like B2 NiAl particles was generated at the interface. The BCC NiAlFe phase is coherent with the matrix and has numerous crystal defects inside the precipitates, whereas the B2 NiAl phase has a stable structure without stress fluctuation because of its greater maturation degree.

Study on mechanical behavior and fatigue life of defective ropes in HTHP gas well with high-sulfur content

As demand for energy increases, the number of “three-high” (high-pressure, high-yield, high-sulfur) gas Wells has doubled, the severe stress fluctuation of pipe string caused by downhole high-pressure environment leads to the failure of rope fracture is particularly prominent. It is easy to cause pipeline blockage and large amount of high-pressure toxic gas leakage caused by tool string accidental falling. Therefore, based on the theory of Love and elastoplastic contact theory, and considering the influence of Poisson’s ratio effect, this article establishes a calculation model for tensile fatigue of interaction between rope strands to study the influence of key structural parameters and breaking wire position on stress distribution and fatigue life of rope. The results show that: the core strand of the rope is the main force position, the overall stress shows the trend of decreasing with the increase of winding radius; when the rope is stretched, the axial deformation near the core of the rope is smaller than the deformation far from the core; under the same number of broken wires, the fatigue life of different ropes is related to the location of broken wires, the farther the location of broken wires from the core of the rope, the higher the fatigue life. The research work in this article provides theoretical guidance for the safe operation of ropes in “three-high” gas wells.

Experimental study on the effect of particle breakage on the shear characteristics of large-displacement soil exposed to heat treatment

Ring shear tests were performed in this study to investigate the large-displacement shear characteristics of quartz sand samples subjected to different degrees of volume effect and high temperature. The influencing principles of normal stress, temperature, and particle breakage on the large-displacement shear characteristics of the specimens were obtained. The influencing mechanism was further elucidated with reference to a previous study. On the basis of an analysis of the similarities and differences between the large-displacement shear behavior of samples before and after exposure to a temperature of 800 °C, we believe that samples impacted by temperature, particle breakage, and normal stress exhibit strain softening under large-displacement shear behavior that has an upper limit of approximately 600 kPa after heat treatment. Meanwhile, the high temperature affects the shear characteristics of the basal facies of a landslide by influencing the rock and soil breakage. The difference in the interlocking forces caused by the particle shape and breakage and the resulting fluctuation of the shear stress are further discussed.

#4504 QUANTITATIVE CHANGES IN INTRACARDIAC FLOW PARAMETERS DURING HEMODIALYTIC SESSIONS

Abstract Background and Aims Hemodialysis sessions exert an acute impact on cardiac geometry and mechanics. The recent development of quantitative measurement of intracardiac fluid-dynamics and analysis of vortexes offers a new opportunity to better understand the fine changes in intracardiac hemodynamic associated with hemodialysis sessions. Vortexes rise in cardiac chambers from blood flow and they are defined as circular fluid structures with rotational movement around a central virtual axis, capable of storing kinetic energy during rotation. They must be distinguished from turbulences, in which various vortexes of different sizes coexist chaotically, resulting in a rapid dissipation of kinetic energy. Our aim was to assess the impact of a hemodialytic session on new parameters originated from intracardiac flow dynamics. Method We included 26 consecutive patients on chronic hemodialysis in clinically stable phase. They underwent echocardiography including intracardiac fluid-dynamic analysis by Color Vector Flow Mapping (Hyperdoppler) before and after a single dialysis session(Fig. 1-A). Patients with hemodynamically relevant valvular disease were excluded. A complete fluid-dynamics evaluation included the measurement of multiple parameters such as vortex area (VA); vortex length (VL); vortex depth (VD). Bland Altman Plot has been used to assess intra and inter-observer variability. Changes in fluid dynamics after dialysis sessions were tested using the Wilcoxon matched-pairs test. Results The Mean Vortex Area (VA) (p = 0.034) (Fig. 1-B), Vortex Depth (VD) (p = 0.024) (Fig. 1-C) and Vortex Length (L) (p = 0.037) (Fig. 1-D) were significantly reduced after the dialysis session. A similar trend towards the reduction of Direct Flow (DF) parameter after the session was found, which was significantly larger for patients with larger baseline left ventricular (V) end-diastolic diameter (r = 0.446; p = 0.037) (Fig. 1-E). On the other hand, mean Vortex Intensity (VI) was significantly increased after dialysis (p = 0.046) (Fig. 1-F). Among energy parameters, the intradialytic change in Kinetic Energy Fluctuation (KEF) (r = 0.4; p = 0.058) and Shear Stress Fluctuation (SSF) (r = 0.435; p = 0.038) (Fig. 1-G) were most closely correlated with intradialytic weight change. Fluid dynamic parameters had similar trends of intradialytic change, with stronger correlations among geometric parameters. Delta changes in VA were closely related to changes in VI (p&amp;lt;0.001) or LV (p&amp;lt;0.001). VI was also correlated with VL (p&amp;lt;0.001) and with Kinetic Energy Dissipation (KED) (p = 0.030), which was also correlated with VL (p = 0.044). KEF was correlated with KED (p = 0.001) and SSF ( = 0.022). Finally, changes in SSF were correlated with those in Flow Force Parameter (p = 0.033) and Flow Force Angle (p = 0.034), that were very closely correlated each other (p&amp;lt;0.001). Conclusion This is the first study assessing the impact of haemodialytic sessions on intracardiac flow dynamics. Measurement of hyperdoppler indices on haemodialysis chair was feasible and reliable in the whole population. Our results uncovered quantitative changes of echocardiographic parameters of vortex geometry and energy during haemodialysis.

Research on Micromechanical Behavior of Current Collector of Lithium-Ion Batteries Battery Cathode during the Calendering Process

Calendering is a crucial process in the manufacturing of lithium-ion battery electrodes. However, this process introduces several challenges to the current collector, including uneven stress distribution, stress concentration, and plastic pits, which ultimately impact electrode consistency and safety. It is important to note that the load exerted on the current collector during calendering cannot be determined solely through experimental means. Moreover, due to the extremely thin nature of the current collector, there is a size effect problem. To address these issues, this study establishes a lithium-ion battery cathode model based on real experimental data and conducts a numerical simulation of the calendering process. By obtaining the load applied to the current collector and incorporating it into the crystal plasticity model, we investigate the mechanical behavior of the current collector at the crystal level during calendering. The results demonstrate that the lithium battery cathode collectors undergo plastic deformation during calendering. Furthermore, current collectors with a smaller number of grains exhibit a more pronounced stress concentration zone, and their stress levels are highly sensitive to the crystal direction. The maximum stress fluctuation range can reach approximately 100 MPa. Conversely, current collectors with a greater number of grains exhibit a more uniform stress distribution during calendering and are less sensitive to the crystal orientation. Their stress levels remain stable within a smaller range, approximately 20 MPa. These findings justify and emphasize the importance of investigating the current collector at the microscopic level, thereby providing valuable research insights for the field of calendering.

Influence of pulsed and alternating flow on the filtration performance during skim milk microfiltration with flat-sheet membranes

Control of deposit formation during skim milk microfiltration (MF) remains challenging, particularly in membranes with spacer nets between membrane layers like flat-sheet and spiral-wound membranes, due to the extensive occurrence of flow shadows behind spacer filaments. One approach to improve process control and efficiency is applying pulsed or alternating flow, which creates regular fluctuations in shear stress, pressure and, for alternating flow, in flow direction. This study assessed the effects of these alternative flow types and compared them to conventional steady crossflow on deposit formation and filtration performance. Flux and protein permeation were monitored during filtration. After filtration, the membranes were removed and deposited proteins stained by Coomassie-blue. The visual analysis of the stained membranes confirmed that the alternative flow types improved access to flow shadows behind spacer filaments by causing a significantly reduced deposition or enhanced removal. Consequently, the reduced deposit formation with pulsed and alternating flow led to enhancements in the steady-state whey protein mass flow by > 8% and > 37% over any steady flow conditions. Considering the flow-specific pump energy demands, pulsed and alternating flow not only improved filtration performance, but also reduced specific energy consumption relative to whey protein mass transfer by > 60%.

Origin of steady state stress fluctuations in a shear-thinning worm-like micellar system

Large, irregular stress fluctuations under a constant applied shear rate are observed during the flow of dilute worm-like micellar solutions even at low Reynolds numbers. Statistical properties of such fluctuations showing signatures of chaos and elastic turbulence have been studied extensively. Although the mechanisms like boundary slippage, dynamics of shear band interface, time-dependent secondary flows, and inertio-elastic effects are conceived as the possible factors for such striking flow properties, their contributions in different non-linear flow regimes remain poorly understood. Here, we study the Taylor–Couette flow of a well-characterized aqueous worm-like micellar system formed by 2 wt. % cetyltrimethylammonium tosylate and 100 mM sodium chloride (2 wt. % CTAT + 100 mM NaCl). For a fixed applied shear-rate just beyond the onset of shear-thinning, high-speed optical imaging in the flow-gradient plane reveals spatiotemporally varying velocity gradients in the system. In this regime, the magnitude of stress fluctuations remains insignificant. However, the fluctuation becomes substantial beyond a critical shear rate deep inside the non-linear regime of the flow curve when significant free-surface undulations, sustained stick-slip, and elastic recoil events are observed. Imaging in the flow-vorticity and the gradient-vorticity plane indicates that such dynamics are primarily driven by the elasticity-induced turbulent flows in the system. Furthermore, in this regime, we find that the characteristic persistent time of stress fluctuations matches well with the time scales of the stick-slip events, as well as the micellar breaking time, indicating a possible connection between the striking stress dynamics and the micellar kinetics.