Effect Of Yield Stress Research Articles

Yield Stress Effects on the Dynamics and Liquid Film Thickness of a Taylor Bubble Rising in Vertical and Inclined Tubes

Yield Stress Effects on the Dynamics and Liquid Film Thickness of a Taylor Bubble Rising in Vertical and Inclined Tubes

The isolated effect of yield stress in viscoplastic turbulent flow

Turbulent flows of viscoplastic fluids are present in several industrial and natural applications. The effects of yield stress on this problem have always been studied as a part of a larger physical context, because real viscoplastic materials have many properties that cannot be easily isolated. Direct numerical simulations have recently emerged as a viable tool for investigating non-Newtonian fluid flow in turbulent regimes. In the present work, we solve the turbulent flow of an ideal Bingham fluid, focusing on the isolated effect of yield stress. A numerical scheme for viscoplastic flows was implemented based on the lattice Boltzmann method. An outstanding characteristic of this scheme is the possibility of representing infinite viscosity by setting the relaxation frequency to zero, enabling the representation of the Bingham constitutive equation without artifacts, and producing a more accurate representation of the yield surfaces. In the turbulent channel flow simulations, the friction Reynolds number was fixed at 180, while the Bingham number varied from 0 (Newtonian) to 0.15. It is shown that unyielded portions of material travel along with the flow near the centerline. These unyielded spots do not disappear quickly, but rather have a significant lifetime. Another interesting outcome is that the yield stress increases the turbulence anisotropy, by lowering the spanwise and normal velocity fluctuations, while the streamwise component becomes higher. Reynolds stresses and budgets of turbulent kinetic energy have been analyzed regarding the increased bulk velocities that were found by increasing the yield stress.

Yield-stress effects on spontaneous imbibition in paper-based kits

The classic Richards equation is a good model for predicting imbibition of viscous fluids in porous materials such as dry soils or filter papers. It cannot, in principle, be used for physiological fluids such as blood simply because such fluids often exhibit a variety of non-Newtonian behavior such as a yield stress. In the present work, we have theoretically extended the classic Richards equation to viscoplastic fluids obeying the Bingham model using the concept of the effective viscosity together with the bundle-of-tube model. The new imbibition model could partly resolve the discrepancy reported in the literature between the predictions of the classic Richards equation for the stain growth of sessile blood droplets in a typical filter paper. A better fit, however, requires considering other non-Newtonian effects of the blood such as its viscoelasticity. Using the Bingham-modified Richards equation, it is demonstrated that yield stress in a test fluid has a retarding effect on the imbibition phenomenon, so that such fluids may not necessarily reach the test line of a paper-based diagnostic kit. But yield stress is predicted to extend the duration of the quasi-steady regime on the test line of diagnostic kits, which is a desirable effect. The results suggest that inducing (or elevating) the level of yield stress in a test liquid such as blood can be used as a passive means to control imbibition characteristics in paper-based systems.

Regulation of the size and flow pattern of yield stress droplets in flow-focused microchannels by orifice constraints

Although droplet microfluidics have attracted increasing research interest, the regulation of complex polymeric droplets remains incomplete in chemical industry. In this study, we investigate the formation of yield stress droplets in flow-focused microchannels with orifice constraints by means of numerical simulations using a volume-of-fluid method coupled with an adaptive mesh refinement technique. The results show that different orifice sizes induce various flow patterns, including dripping, quasijetting, quasijetting with droplet coalescence, and jetting. A predictive model is established for the extension length of the dispersed phase during the necking stage, considering orifice dimensions interplay. Furthermore, higher yield stress influences the droplet size and formation frequency by expanding the high viscosity distribution in the dispersed phase. The proposed predictive correlations for droplet size, velocity, and formation frequency, accounting for the effects of orifice dimensions and yield stress, are believed to have significant impacts on the preparation of polymeric droplets in microreactors.

Natural convection of viscoplastic fluids in a triangular enclosure

This study extends the analysis of natural convection in a viscoplastic fluid to flow within a triangular enclosure. The finite-element approach provided a numerical solution to the continuity, momentum, and energy equations. The governing parameters for this problem are the Rayleigh number, (Ra=104−106), yield number, (Y=0−Ymax), aspect ratio, (HL=0.5−2.5), and slope angle, (∅=0−π2). The influence of these parameters on the heat and mass transfer, morphology of yielded/unyielded regions, and fluid flow were thoroughly examined. The results show that two opposing factors influence the flow behavior and heat transmission within the triangular enclosure. The proximity of the walls restricts the convective movement, leading to reduced heat transfer. However, the proximity of hot and cold sources increases the temperature gradient and heat transfer. The unique influence of the viscoplastic material properties, particularly the yield stress, further distinguishes the heat transfer in this triangular enclosure from other geometries. The results indicate that an increase in the Rayleigh number mitigates the effects of yield stress to some extent. However, the accumulation of unyielded material at the triangular apex hinders convection flow. Furthermore, the viscoplastic fluid flow and heat transfer changed significantly with changes in triangle height. In particular, the maximum yield stress increased by more than 100 % as the aspect ratio increased from 0.5 to 2.5. A change in the slope angle causes a continuous transition from subcritical to supercritical bifurcation, significantly affecting the morphology of the yielded and unyielded areas, and the maximum (critical) yield number. Finally, correlations were developed to predict the Nusselt number and maximum yield stress in all cases.

Turbulent impingement jet cleaning of thick viscoplastic layers

An experimental study is conducted on the use of a normally impinging turbulent water jet (with the Reynolds number of Re≈11800), for cleaning thick layers of a Newtonian fluid and two viscoplastic fluids (i.e., transparent Carbopol solutions). The layer thickness is larger than the jet radius. Non-intrusive techniques are used to track the geometrical features of the cleaning process in real time. The effects of layer thickness and fluid yield stress on removal behavior, including cleaning radius, cavity radius, and angle, are investigated. A yield stress promotes the initial formation of a blister rather than a cavity, and the rate of removal decreases with increasing layer thickness and yield stress. A relation is presented for the growth of the cavity radius, which fits our experimental observations well. A comparative analysis of submerged and impinging jets reveals, for the first time, the role of air entrainment in the process, with bubble characteristics such as trajectory, size distribution (diameter), and velocity being determined by the yield stress.

Fully optimized second-order estimates for the macroscopic behavior and field statistics of particle-reinforced viscoplastic composites

This paper is concerned with the characterization of the macroscopic behavior and statistics for the distribution of the stress and strain-rate fields in composites consisting of random and isotropic suspensions of rigid spherical particles in power-law viscoplastic materials. For this purpose, use is made of the Fully Optimized Second-Order (FOSO) homogenization method (Ponte Castañeda, 2016) in combination with recently developed estimates (Kammer and Ponte Castañeda, 2022) for the macroscopic properties of the associated ‘linear comparison composite’ (LCC). Special attention is devoted to the method’s ability to account for the dependence of the homogenized properties of the nonlinear composite on the Lode angle (third invariant) of the applied loading. It is found that, while, for large particle volume fractions c, the effective flow stress is only weakly dependent on the Lode angle, for dilute volume fractions, the dependence on the Lode angle becomes more pronounced. In the ideally plastic limit, as c tends to zero, the effective yield stress is shown to depend linearly on c for axisymmetric shear, while this dependence becomes weaker with a non-analytic leading-order correction of O(c/lnc) for pure shear loading. This strong dependence on the Lode angle at dilute concentrations is shown to be due to significant differences in the local deformation patterns, which become strongly anisotropic and localize for pure shear conditions, but do not for axisymmetric shear. In turn, the FOSO homogenization method is able to capture the statistical features of these different deformation patterns by providing consistent estimates for the covariance tensor of the strain-rate field fluctuations in the matrix phase, which tend to become more strongly anisotropic for the pure shear case. As c increases, the shear bands are deflected by the randomly dispersed spheres leading to a more isotropic distribution of the stress and strain-rate fields, which is consistent with a weaker Lode angle effect. The estimates can also capture the effect of strong particle interactions, including the existence of a rigidity threshold where the macroscopic flow stress and field fluctuations blow up.

Flow analysis of screw extrusion in three-dimensional concrete printing

Recent advances in three-dimensional concrete printing necessitated the detailed understanding of the operation and performance of screw extruders. This paper shows that the volumetric output rate can be approximated using the rotating barrel and stationary screw assumption (drag flow equation), which is used routinely in polymer melt extrusion calculations. Verification is provided by comparisons to experimental results available in the literature and to computer flow simulations for fluids with yield stress. Significant insight is obtained using fully three-dimensional simulations. This includes particle pathlines, which form “a helix within a helix,” axial pressure profiles, and the effect of yield stress, which is relatively small on the output rate but large on torque and power. The computer simulation also predicts unyielded flow zones in the extruder channel at low screw rotation speeds.

Modeling extrusion process and layer deformation in 3D concrete printing via smoothed particle hydrodynamics

We developed a computational framework to simulate the intricate processes of extrusion and layer deformation in 3D concrete printing (3DCP). A novel two-dimensional (2D) virtual printing scheme is proposed that enables direct prediction of cross-sectional shape, releasing simulations from the constraint of rectangular nozzles inherent in traditional 2D models. The proposed scheme accurately captures significant lateral deformation, previously ignored by conventional 2D models. It is noteworthy that, for the first time, the effect of time-dependent yield stress on layer deformation is considered by introducing the structuration rate. Further, to leverage advantages in avoiding mesh generation and additional interface tracking, a weakly compressible smoothed particle hydrodynamics (SPH) method incorporating the regularized Bingham model is equipped in the proposed framework. The simulated cross-sectional shapes exhibit excellent consistency with experimental results and outperform existing numerical results across various nozzle heights, printing velocities, and extrusion velocities. Our exploration of rheological parameters reveals that the final layer deformation is influenced by the yield stress, while its deformation rate is affected by the plastic viscosity. The proposed virtual printing framework emerges as a promising tool for enhancing predictability and efficiency in the printing process.

Novel framework for predicting constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations

Fracture toughness is dependent on geometry according to a phenomenon known as the constraint effect on fracture toughness. In this paper, we propose a framework to predict constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations. An elastic–plastic material was adopted because constraint effects are typically related to plastic deformation at the crack tip. Modified boundary layer formulations were used as loading methods to control phase field evolution at the crack tip. Numerical results indicate that fracture toughness increases with negative T-stress. The effects of yield stress and the linear hardening coefficient on constraint effects were also investigated. The results revealed that the variation in fracture toughness was greater in materials with low-strain hardening and yield stress compared to that in materials with high-strain hardening and yield stress. Finally, the variation in cleavage fracture toughness as predicted by our framework with a limited set of available experimental data was evaluated. The trend of the predicted results is consistent with that of the experimental results.

Performance of digital image correction technique for mild steel with different strain hardening effects

This paper investigates the performance of Digital Image Correction (DIC) technique in determining the initial fracture toughness of mild steel with different strain hardening effects. To achieve this goal, the results of DIC technique-based method are compared with those of the commonly used unloading compliance (UC) method. The comparison results reveal that the DIC technique-based method exhibit a good agreement with the UC method in determining initial fracture toughness, with a deviation of less than 3.0 %. Additionally, the DIC technique-based method demonstrates the consistency in determining the initial fracture toughness, independent of the ratio of initial pre-crack length to width. Furthermore, the importance of strain hardening effects on initial fracture toughness follows the order of strain hardening capacity, effective yield stress, and yield offset. The significance of this paper is that it provides a deep understanding of the performance of the DIC technique in determining the initial fracture toughness of mild steel.

Comparison between methods for determining the effective vertical yield stress of intermediate fine-grained soils.

Effective vertical yield stress (σ'xy) is essential in accurately describing fine-grained soils' mechanical properties and their behaviour under load over time. It helps assess settlements and stress history. In most constitutive models, this parameter indicates changes in the soil behaviour due to the development of recoverable and irrecoverable strains resulting from loading. The results of oedometric compression tests for 25 soil samples with a wide range of plasticity parameters were used for the investigation. The intermediate fine-grained soils comprised different proportions of clayey, silty and sandy fractions. An in-depth, two-staged statistical analysis was carried out to compare twelve methods of determining effective vertical yield stress, namely: Casagrande (CM), Pacheco Silva (PSM), Butterfield (BTM), Oikawa (OIM), Onitsuka (ONM), Boone (BM), Becker (WM), Morin (WPUVSM) Wang & Frost (DSEM), Tavenas (SEM), Senol (SLSEM), and Janbu (JM). It aimed to check the association of these methods and the consistency of the obtained results. Based on the difference analysis, the methods originated in the work approach (i.e. WM, WPUVSM, DSEM) and CM gave comparable σ'xy values. The methods utilised bi-logarithmic plots (i.e. BTM, OIM, ONM) received slightly greater or lesser σ'xy values than BM and JM. The remaining methods were characterised by medium to the high variability and were sensitive to even the slightest disturbances resulting from the procedure of determining σ'xy.

IMPACT OF HALL CURRENTS AND ION SLIP ON MIXED CONVECTIVE CASSON WILLIAMSON NANOFLUID FLOW WITH VISCOUS DISSIPATION THROUGH POROUS MEDIUM

This article emphasizes Hall currents and ion slip impact on Casson Williamson nanofluid. Inclusion of viscous dissipation over a mixed convective porous medium is considered. Similarity transformation is used to convert governing equations to ordinary differential equations. Fifth order Runge-Kutta- Fehlberg scheme via shooting technique is utilized to solve highly non-linear PDEs. Physical mechanisms of various parameters are portrayed graphically and well explained. Major outcome reveals the velocity profile of Casson Williamson fluid parameters. Strong effects of yield stress with viscous force reduce the velocity flow. Consequently, the temperature and concentration profile of mixed convection, hall, and ion slip parameters are discussed. To validate the present study, comparisons are done with existing literature.

Analysis of the Effect of Yield Stress on Stress Corrosion Cracking of Martensitic and Ferritic Steels in Acidic Environments

Analysis of the Effect of Yield Stress on Stress Corrosion Cracking of Martensitic and Ferritic Steels in Acidic Environments

Pore-Scale Simulation of Fracture Propagation by CO2 Flow Induced in Deep Shale Based on Hydro-Mechanical Coupled Model

Summary The depletion of conventional reservoirs has led to increased interest in deep shale gas. Hydraulic fracturing addresses the challenge of developing low-permeability shale, involving hydro-mechanical coupling fracture propagation mechanics. Supercritical CO2 (SC-CO2) has become a promising alternative to fracturing fluids due to its ability to be buried underground after use. The high temperature, pressure, and stress of deep shale lead to the flow of fracturing fluid to plastic deformation of rock, resulting in microfractures. In this paper, we simulate the fracture propagation process of deep shale fractured by SC-CO2 based on the coupling of the Darcy-Brinkman-Biot method, which adopts the Navier-Stokes-like equation to solve the free flow region, and the Darcy equation with Biot’s theory to solve flow in the matrix. To clearly probe the mechanism of deep fracturing from a microscopic perspective, the plastic rock property is taken into consideration. We investigate the effects of injection velocity, rock plastic yield stress, formation pressure, and gas slippage effect on fluid saturation and fracture morphology, and find that increasing the injection rate of fracturing fluid can form better extended fractures and complex fracture networks, improving the fracturing effect. Furthermore, we find that it is more appropriate to adopt SC-CO2 as a fracturing fluid alternative in deep shale with higher plastic yield stress due to higher CO2 saturation in the matrix, indicating greater carbon sequestration potential. High confining pressure promotes the growth of shear fractures, which are capable of more complex fracture profiles. The gas slip effect has a significant impact on the stress field while ignoring the flow field. This study sheds light on which deep shale gas reservoirs are appropriate for the use of SC-CO2 as a fracturing fluid and offers recommendations for how to enhance the fracturing effect at the pore scale.

Surfactant amplifies yield-stress effects in the capillary instability of a film coating a tube.

To assess how the presence of surfactant in lung airways alters the flow of mucus that leads to plug formation and airway closure, we investigate the effect of insoluble surfactant on the instability of a viscoplastic liquid coating the interior of a cylindrical tube. Evolution equations for the layer thickness using thin-film and long-wave approximations are derived that incorporate yield-stress effects and capillary and Marangoni forces. Using numerical simulations and asymptotic analysis of the thin-film system, we quantify how the presence of surfactant slows growth of the Rayleigh-Plateau instability, increases the size of initial perturbation required to trigger instability and decreases the final peak height of the layer. When the surfactant strength is large, the thin-film dynamics coincide with the dynamics of a surfactant-free layer but with time slowed by a factor of four and the capillary Bingham number, a parameter proportional to the yield stress, exactly doubled. By solving the long-wave equations numerically, we quantify how increasing surfactant strength can increase the critical layer thickness for plug formation to occur and delay plugging. The previously established effect of the yield stress in suppressing plug formation [Shemilt et al., J. Fluid Mech., 2022, vol. 944, A22] is shown to be amplified by introducing surfactant. We discuss the implications of these results for understanding the impact of surfactant deficiency and increased mucus yield stress in obstructive lung diseases.

Numerical simulation of fresh concrete flow in the L-box test using computational fluid dynamics

Concrete remains a widely used material in construction. As structures become more optimised, a deeper understanding of the rheology of the concrete mixture is necessary. This paper aims to numerically simulate the flow of fresh concrete in the L-box apparatus, with the objective of gaining insights into its rheological behaviour and predicting its properties. The fresh concrete flowing through the L-box test is simulated from the moment that the gate is lifted until the stoppage and the material takes its final shape. The flow in this tool occurs on a free surface. In this work, a three-dimensional model has been developed using the computational fluid dynamics technique for simulation. The flow behaviour of fresh concrete was assumed to be non-Newtonian following the Bingham law, characterised by a non-linear shear stress–shear rate ratio, yield stress and plastic viscosity. A set of numerical simulations by varying workability were conducted. Furthermore, a parametric study was conducted to examine the impact of introduced parameters in the concrete flow, including the effect of yield stress, viscosity and density.

Heat transfer in the Jeffery-Hamel flow of a yield-stress fluid

Heat transfer in the Jeffery-Hamel flow of a yield-stress fluid that obeys the Bingham-Papanastasiou model is investigated in the present study. Among various rheological models proposed to formulate the flow of yield-stress fluids, the Bingham model is usually used to address the effect of yield-stress. A fluid that obeys the Bingham model does not show any shear-thinning or shear-thickening behaviors; this makes the interpretation of the results much easier. Addressing the unyielded regions (regions at which the yield-stress material behaves like a solid) in a yield-stress fluid flow is not a trivial task, and it could be impossible, especially in complex geometries. Unfortunately, the Bingham model itself cannot be used to formulate complex fluid flow problems due to the mathematical difficulties (i.e., addressing the unyielded regions); hence it is usually regularized to avoid these mathematical challenges. One of these regularized models is the Bingham-Papanastasiou model. Using an exponential term enables the Bingham-Papanastasiou model to address the unyielded regions. However, this exponential term results in highly non-linear equations, which are difficult to be handled mathematically. In the present study, the effect of the yield-stress (Bingham number) on the hydrodynamics and heat transfer in the Jeffery-Hamel flow is investigated by using the Bingham-Papanastasiou model. The momentum transfer in the Jeffery-Hamel flow of a Bingham-Papanastasiou fluid is governed by a highly non-linear ordinary differential equation (ODE) which is a boundary value problem. Assuming that the fluid's properties are independent of the temperature and pressure, this highly non-linear ODE is solved numerically. The heat transfer in the flow, with a constant wall temperature boundary condition, is investigated, assuming the flow to be an equilibrium viscous dissipation flow (the fluid's mixed mean temperature variation is negligible along the channel). The resultant linear energy equation is also solved numerically to obtain the temperature distribution across the channel. The results obtained in this work show that the yield-stress increases the wall shear stress, Nusselt number, and Stanton number. In fact, the effect of the yield-stress on the Nusselt number is comparable to the effects of Prandtl and Eckert numbers. It is also found that the yield-stress can prevent the flow separation in a divergent channel. Considering the advantages of using the yield-stress fluids as the working fluids in the Jeffery-Hamel flow, they can be considered as an alternative to nanoparticles which are usually used to enhance the fluid's thermal conductivity and also the Nusselt number.

Flow simulation of fresh concrete accounting for vibrating compaction

Vibrating compaction is necessary for consolidating fresh concrete into form because it decreases inter-particle friction, which dramatically improves fluidity. Thus, vibrating compaction improves the workability and compactness of concrete and can even increase its density, strength, and durability. Nevertheless, the effect of vibrating compaction on the filling ability of normal concrete has rarely been discussed despite its importance. This paper introduces a numerical approach to estimating concrete-filling ability at vibration conditions. The vibration attenuation of a poker-type concrete vibrator is quantified using a vibration energy diffusion model, and the rheological behavior of fresh concrete under vibration is generalized. Then, volume-of-fluid (VoF) simulations taking into account the vibrating compaction are conducted to obtain the filling profiles. The simulation results provide a reasonable estimation, based on a comparison with the results of mock-up testing. The effects of attenuation coefficient, yield stress, and plastic viscosity on compacting efficiency are also discussed. In summary, the proposed method can estimate the filling of fresh concrete according to concrete rheology and attenuation of vibration.

Limit elastic speed analysis for functionally graded rotating beam

This study aims to determine the limit elastic angular speed of the rotating beam made up of functionally graded material. The speed at which the material yielding is instigated is termed as limit elastic speed. Assuming material distribution as function of power law, modified rule of mixture was used to determine the distribution of material properties and later was used to calculate the effective yield stress for different volume fraction index. A metal matrix of aluminium has been considered with a reinforcement of silicon carbide. The B-spline collocation method has been used to solve the governing equation obtained using the principle of virtual work. This paper outlines the effect of volume fraction on the deformation and stress at limit elastic speed; influence of slenderness ratio on the limit speed was also reported.