Shear Yield Stress Research Articles

Preparation and characterization of a novel MR fluid with MWCNTs/GO composites coated ferromagnetic particles

Magnetorheological (MR) fluid is a typical intelligent material which is widely adopted in the mitigation of civil engineering structures, and it is normally composed of nano-sized or micro-sized iron particles, carrier fluids and additives. In the study, ferromagnetic particles coated with multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO) composites were prepared with grafting technology and the influence concerning ratio of MWCNTs, GO, grafting agent as well as carbonyl iron (CI) particles was studied to select the composite ferromagnetic particles which have the best effects of coating through surface topography analysis. In addition, the MWCNTs/GO composites coated CI particles and surfactants-modified CI particles were combined together to prepare a series of MR fluids with different ratio of the two compound ferromagnetic particles, volume fraction of total ferromagnetic particles and additives by the control variable method and the influence of the factors on the performances of MR fluids was investigated through sedimentation stability, re-dispersion, zero field viscosity and shear yield stress tests. The test results presented that the introduction of MWCNTs/GO composites coated CI particles was beneficial to the improvement of stability with sedimentation rate lower than 6%.

Study on asymmetrical cold rolling considered sticking friction

A new model considered the sticking friction for analyzing the asymmetrical cold rolling process is proposed by the slab method. This friction model is composed of the Coulomb friction model and yield shear stress. The analytical models of the rolling pressure are given respectively based on Coulomb friction model, constant friction model and Orowan friction model to compare the effects of different friction models on the friction stress and rolling pressure. The proposed model can avoid the problems of the friction stress exce eding the yield shear stress in Coulomb model and the friction factor m>1in the mixed friction model. The influences of the rolling parameters on the friction stress and the proportion of the sticking zone in the deformation zone are analyzed. The results show that the proportion of the sticking zone increases with the increases of the reduction rate, friction coefficient and roll radius, and decreases with the increases of the roll speed ratio and tensions. The calculated values by the proposed model agree well with the experimental results.

Effect of the Drying Method of Pine and Beech Wood on Fracture Toughness and Shear Yield Stress.

The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An alternative methodology for determination of mechanical properties (fracture toughness and shear yield stress) based on cutting process analysis is presented here. Two wood species (pine and beech) representing soft and hard woods were investigated with respect to four diverse drying methods used in industry. Fracture toughness and shear yield stress were determined directly from the cutting power signal that was recorded while frame sawing. An original procedure for compensation of the wood density variation is proposed to generalize mechanical properties of wood and allow direct comparison between species and drying methods. Noticeable differences of fracture toughness and shear yield stress values were found among all drying techniques and for both species, but only for beech wood the differences were statistically significant. These observations provide a new highlight on the understanding of the effect of thermo-hydro modification of wood on mechanical performance of structures. It can be also highly useful to optimize woodworking machines by properly adjusting cutting power requirements.

Rheological and strength performances of cold-bonded geopolymer made from limestone dust and bottom ash for grouting and deep mixing

This paper aims to research the potential use of cold-bonded geopolymer stabilizer made from limestone dust and bottom ash for grouting and deep soil (clay) mixing. For this purpose, the rheology and strength performances of the cement (PC)-based grouts with the stabilizers of limestone dust (LD), bottom ash (BA), geopolymerized cold-bonded limestone dust (GLD), and geopolymerized cold-bonded bottom ash (GBA) were investigated. The rheometer tests were conducted for the rheological performances at a wide range of stabilizer replacement (0–100%) and water/binder (w/b) ratio (0.75–1.5). Using proper replacements from the grout rheology, the unconfined compressive strength (UCS) tests (7 days, 28 days) were performed for the grouting (w/b = 1) and deep mixing (w/b = 1–1.25). The effect of stabilizer on the failure patterns was also examined from specimens of UCS tests. From the experimental work, the rheology of grout mixtures indicated (i) the adequacy of low amount of stabilizer replacements (< 50%); (ii) the dilatant behavior similar to PC; (iii) a decreasing trend of the shear stress, apparent viscosity, yield stress, and plastic viscosity with the increased w/b; (iv) slight to moderate responses of PC mostly; and (v) a potentially favorable rheology of cold-bonded stabilizers (GLD, GBA) for grout flow and workability regarding the yield stress and plastic viscosity. From the strength tests of grout mixtures (0–40%), the GBA additions yielded higher UCS performances for the grouting. For the deep mixing, both the additions of GLD and GBA were found more successful for the strength. The failure planes of UCS specimens were observed independent from the stabilizer types and dosage rates that dominantly failed in axially or near-axial splitting. From the study, the contributions of GLD and GBA from the potential of cold bonding are relatively promising for grouting and deep mixing.

Linking thermoset ink rheology to the stability of 3D-printed structures

Thermoset polymer composites show promise for additive manufacturing (AM) applications to address some of the limitations of the more widely used thermoplastic feedstock materials. Thermosets offer attractive mechanical properties while providing excellent interlayer bonding, high thermal and chemical stability, and reduced energy consumption as a result of deposition at room temperature. However, since thermoset resins rely on a crosslinking reaction to solidify, rather than quickly cooling like thermoplastics, viscoelastic properties must be relied upon to maintain deposited shape after deposition until crosslinking can occur. This fact has not impeded development and characterization of new thermoset feedstocks on the small scale, but recent efforts to increase scale of thermoset printing have highlighted issues with structural stability under self-weight. This study addresses issues of self-weight by investigating the mechanisms that cause collapse of tall, thin printed walls. Using nanoclay- and fumed silica-filled epoxy feedstocks, this work compares the collapse height for printed walls to stability models based on yielding and buckling mechanics. Inputs for these models – shear yield stress and storage modulus – were taken directly from parallel plate rheometry measurements. Model predictions were found to be in good agreement with experimental results, where both yielding and buckling behavior were observed, provided the rheological properties after a shear excursion were used as inputs. This work establishes a direct link between basic rheological properties of the feedstock, geometry of the printed object, and achievable height. The results presented highlight the importance of understanding recovery behavior in thermoset feedstocks and provide valuable guidance on the development of more effective direct-ink writing feedstock materials.

Sample disturbances due to removal of confining pressure in laminated clay

Sample disturbances in laminated soils may be caused by several factors, including water movement between the clay and sand layers upon removal of overburden pressures. The research reported in this article examined the impact of this water movement on various geotechnical parameters. Samples of kaolin with laminations were formed, subjected to isotropic consolidation and subsequently sheared under undrained conditions. Further tests were carried out in which the samples were isotropically unloaded after consolidation and isotropically reloaded under undrained conditions, followed by undrained shearing. Tests were also carried out to examine the impact of unloading/reloading on the yield stress and small-strain stiffness. The results showed that the isotropic unloading/reloading process under undrained conditions led to reductions in the undrained shear strength, small-strain stiffness and yield stresses. Comparative tests carried out on unlaminated samples showed that the unloading/reloading process had a marginal impact on the above mentioned geotechnical properties.

A constitutive hemorheological model addressing both the deformability and aggregation of red blood cells

Red blood cells (RBCs) in physiological conditions are capable of deforming and aggregating. However, both deformation and aggregation are seldom considered together when modeling the rheological behavior of blood. This is particularly important since each mechanism is dominant under specific conditions. To address this void, we herein propose a new model that accounts for the deformability of red blood cells, by modeling them as deformed droplets with a constant volume, and of their aggregation, by properly characterizing the network formed by red blood cells under small shear rates. To derive the model, we employ non-equilibrium thermodynamics that allows us to consistently couple the two mechanisms and guarantees model admissibility with the thermodynamic laws. Relative to our previous model, which addresses the rheological behavior of non-aggregating deformable red blood cells, one additional structural variable, λ, to properly characterize the network formed by RBCs, and another additional parameter, ε, that quantifies the relative importance between the regeneration/buildup and flow-induced breakup of the network, are considered here. The new model predicts a yield shear stress, in accord with experimental data, but also predicts non-vanishing yield normal stresses. Although no rheological measurements of yield normal stresses of blood have been reported in the literature, the recent measurement of yield normal stresses of other yield stress fluids indicates their potential existence in blood as well. We show that the new model is in complete accord with the experimental rheological behavior of normal blood in both steady-state and transient (step-change in shear-rate) simple shear.

Rheological study of cellulose nanofiber disintegrated by a controlled high-intensity ultrasonication for a delicate nano-fibrillation

Herein, the rheological properties of 2,2,6,6-tetramethylpiperidin-1-oxyl radical-oxidized cellulose nanofiber (TOCNF) suspensions individualized using high-intensity ultrasonication were investigated. The surface charge density of the nanofibers and sonication time were 0.659–1.24 mmol/g and 30–600 s, respectively. With increased surface charge density, the minimum time required for disintegration decreased due to the repulsive force between oxidized nanofibers. Additionally, increased sonication time enhanced the TOCNF nanofibrillation, thereby forming networks between the nanofibers. Further disintegrating TOCNF increased shear viscosity and yield stress of TOCNF suspensions. Based on the crowding factor theory, the relationship between the average fiber width and sonication time was found at various surface charge densities. Ultrasonication was considered as an energy saving and precisely controllable nanofibrillation method. This research shows the change of fiber shapes during the nanofibrillation process, and suggests an estimation of disintegration degree by the relationship between the rheological properties and TOCNF morphology.

Synthesized micro-theoretical analysis of performance of magnetorheological fluids subjected to shear mode operation: transmission, slip and sedimentation characteristics

This paper aims to formulate a synthesized micro-theoretical analysis that consists of transmission, slip and sedimentation characteristics for the evaluation of the performance of magnetorheological fluids (MRFs) subjected to the shear mode operation. To begin, based on the magnetic dipole theory and the typical micro-structure of MRFs, the shear yield stress of MRFs is analyzed considering the contribution of the magnetic force, excluded-volume force and viscous force. Then, an improve micro-structure of MRFs that is in correspondence with the actual observation is built, and the slip power of MRFs per unit area that takes into account the friction of the particles, walls and carrier liquid is investigated. Moreover, the sedimentation characteristic of MRFs described by the sedimentation velocity of the particles with the coating is analyzed based on the Stokes’ rule. The main influencing factors, such as the magnetic field intensity, the volume fraction of particles, the radius of particles, the coating thickness, the shear strain and the shear strain rate, etc, are taken into account in the micro-theoretical analysis, and the effects of these factors on the transmission, slip and sedimentation characteristics of MRFs are investigated respectively. It shows that the micro-theoretical analysis can describe these characteristics of MRFs accurately and reasonably, and can effectively be utilized for the initial design and optimization of the performance of MRFs and the useful guidance on the external control of magnetorheological transmission devices.

Coarse-grained modeling of nanocellulose network towards understanding the mechanical performance

Owing to the impressive mechanical properties and renewability, nanocellulose has been increasingly used for the development of lightweight materials in various applications. Here, we present a coarse-grained (CG) modeling study for investigations of mechanical performance of cellulose-based bulk material consisting of disordered cellulose nanocrystals (CNCs), forming a porous network microstructure. The simulation results reveal that increasing density and cohesive interaction between CNCs leads to an increase in shear modulus and yield stress of bulk system, which strongly depends on the cohesive energy density of the system. Notably, by evaluating the local “molecular” stiffness, the bulk CNCs system tends to become more dynamically heterogeneous with increasing density and cohesive interaction, which is similar to glass-forming liquids such as polymers. Such influence on shear modulus and dynamical heterogeneity of bulk CNCs is found to be more pronounced with variation of density, which is likely due to the high rigidity of CNC and high porosity of network microstructure. Our study provides fundamental insights into the mechanical behavior of bulk nanocellulose under the influences of key microstructural and interfacial features, which is crucial to develop an extension of structure–property relationships as established for engineering materials.

Microstructure evolution based particle chain model for shear yield stress of magnetorheological fluids

To predict the shear stress of magnetorheological fluids (MRFs) under magnetic field and shear flows, a meso-microscale shear model is proposed based on the entire course of particle aggregates and chains. For this purpose, a systematic study on the microstructure evolution and rheological properties of MRFs is conducted by using molecular dynamics simulations. An efficient chain identification technique is introduced to count the number of particle chains within the suspension system. From the perspective of particle-level simulations, the microstructured behavior of MRFs involving particle aggregation and internal structure evolution of magnetorheological suspensions are addressed. Shear properties of MRFs derived by the proposed model are studied, and model verification by comparison with previous experimental data and predictions of the existing structural viscosity model is included as well. It is revealed that the proposed meso-microscale shear model exhibits satisfactory accuracy and efficiency for describing the rheological properties of MRFs. Besides, the critical factors linked with rheological properties of MRFs such as magnetic field strength, particle volume fraction and shear rate, are analyzed, further demonstrating the applicability of the proposed model in design and optimization of MRFs.

Effect of Functional Polycarboxylic Acid Superplasticizers on Mechanical and Rheological Properties of Cement Paste and Mortar

Modern engineering practices require that polycarboxylic acid high-performance superplasticizers have good adaptability to various environments and materials, which indicates the importance of producing functional polycarboxylic acid superplasticizers with a variety of functions. Therefore, in this work, a functional polycarboxylic acid high-performance water-reducing agent, named superplasticizer J, a sustained-release functional polycarboxylic acid high-performance water-reducing agent, named superplasticizer H, and an early-strength functional polycarboxylic acid high-performance water-reducing agent, named superplasticizer Z, are synthesized. The produced superplasticizers were characterized by employing X-ray diffraction (XRD), thermogravimetry, mercury intrusion porosimetry, and rheometry and by measuring heat of cement hydration. The impacts of the functional polycarboxylic acid superplasticizers on the mechanical properties, rheological properties, and cement hydration of the cement pastes and mortars were investigated. The results show that the prepared functional polycarboxylic acid superplasticizers fulfill water-reducing and cement dispersion functions, can improve the fluidity and plasticity of the mortar, and have a greater effect on reducing shear yield stress and increasing plastic viscosity compared to the naphthalene-based superplasticizers. The sustained-release functional polycarboxylic acid high-performance superplasticizer H performs an excellent slump retention function, and the early-strength functional polycarboxylic acid high-performance superplasticizer Z has a significant effect on improving the early and late strength of the mortar.

Microstructural dependence of the incipient to homogeneous flow transition in metallic glass composites

As ductile derivatives of amorphous alloys, metallic glass composites balance high strength with the ability to mitigate catastrophic shear localization, which has long plagued monolithic metallic glasses. In this study, we employ a bonded-interface indentation technique coupled with strain field mapping to identify the governing yield criterion in metallic glass composites as a function of their microstructural length scales. A crossover from the shear plane to maximum shear stress yield criterion is uncovered at a crystalline fraction of approximately 60%, thus signaling an effective transition from incipient to homogeneous flow as the dominant deformation mode of the composite microstructure.

Solid expandable tubular forming behavior based on twin shear stress yield criterion: Analytical, numerical simulation and experiment

Abstract Solid Expandable Tubular (SET) technology is a recent important breakthrough in petroleum exploration and drilling. The expansion forming theory and the constitutive model of the tubular materials are the theoretical basis for the development of this technology. This work focuses on establishing analytical and finite element models on the basis of the Twin Shear Stress (TSS) yield criterion to investigate the forming behavior of solid expandable tubular. The expansion force expression of the power exponential hardening material model was derived. A constitutive model using the TSS yield criterion and related flow rules was proposed and implemented into the ABAQUS software. Further to this, variations of the expansion forces, residual stresses and plastic deformation under different expansion ratios and friction coefficients were investigated. In addition, a tubular expansion experiment was conducted to validate the analytical and finite element solutions. Results show that the expansion force expression is reliable, but there are discrepancies within a reasonable range. The finite element model is capable of predicting the expansion forces, residual stress distributions, thickness reduction and length shortening accurately. Moreover, it is found that the expansion ratio should be controlled below 35% to avoid burst and collapse of the expandable tubular in practical application. For expansion operations, suitable lubrication conditions should be determined to ensure an acceptable expansion force and maintain a certain friction coefficient.

Mathematical modelling of the influence of yield shear stress on blood friction in a turbulent flow

Measurements of blood rheology indicate that human blood has a yield shear stress. Transport of oxygen in the aorta or a vein depends on blood flow rate. Therefore, it is interesting to find out how blood yield shear stress affects blood transportation if flow is turbulent. The majority of mathematical approaches deal with laminar flow of human blood, which is rather simple compared to turbulent flow modelling. This paper presents a mathematical model of fully developed turbulent flow of human blood in the aorta. The physical model assumes that blood is a non-Newtonian liquid that demonstrates yield shear tress. The main objective of the research is to examine the influence of human blood yield shear stress on turbulent properties, like friction factor, in the aorta. Available blood rheology experimental data for various concentrations of haematocrit were used in order to fit the rheological model. The rheological model together with the momentum equation and the two-equation turbulence model constitute a mathematical model of turbulent flow of human blood. Results of simulations are discussed and presented as figures and conclusions.

Soil solution composition affects microstructure of tropical saline alluvial soils in semi-arid environment

The remediation of soils stressed by salinity improves soil quality for food production. However, information on how remediation techniques affect microstructural stability/elasticity and resistance is lacking. Hence, the objective of this study was to characterize the microstructure of saline alluvial soils from a semi-arid environment, and to evaluate how the techniques of leaching soil and Na+ substitution by other cations affect the microstructure strength and elasticity evaluated by rheological techniques. Homogenized soil of sixteen horizons of four salinized soil profiles (an Abruptic Solonetz, a Eutric Gleysol, and two Hypereutric Planosols) were collected in Northeast of Brazil. Each horizon was analyzed separately in a completely randomized design, with three replications. The treatments corresponded to soils saturated with 1 × 10−4 mol m−3 of KCl (+K), CaCl2 (+Ca) or MgCl2 (+Mg), leaching of salts (LS) by successive leaching with alcohol 60%, and untreated soil (control). The soils were submitted to an amplitude sweep test with controlled strain in a compact modular rheometer. The obtained variables were strain and stress at the end of the linear viscoelastic interval (LVR) (γLVR and τLVR, respectively), strain (γYP) and stress (G’YP) at the yield point, shear stress (τmax), and integral Z (Iz). The rheological properties varied greatly between the horizons of the same soil profile. The LS increased γLVR compared to control, while the saturation with cations caused reduction in γLVR, especially in soils of higher clay content. The saturation with saline solution increased γYP and Iz, with greater effect in + K treatment. Both leaching of salts and cation saturation increased soil shear strength at the end of the LVR and at the yield point. Leaching of salts caused destabilization of soil microstructure, which is an important finding that needs to be addressed by measures accompanying remediation of salinized soils to maintain soil physical quality.

A critical examination of the influence of material characteristics and extruder geometry on 3D printing of cementitious binders

Extrusion pressure-displacement tests on cementitious pastes with multiple starting materials and differing particle packing, subjected to different extrusion geometries are reported. The steady state extrusion pressure (equivalent to extrusion yield stress) and the deadzone length (static zone of material buildup at die entry) are determined from the pressure-displacement response to characterize the extrudability and/or printability. A unique “geometric ratio” is used to account for the effects of barrel-die geometry on paste extrusion. The ratio of extrusion yield stress (25–75 kPa) to the measured shear yield stress (50–300 Pa), the deadzone length, and the measured-to-designed filament volume at a given flow rate (print speed) are found to remain relatively invariant with geometric ratio for mixtures with high degree of microstructural packing, and thus better extrudability and shape stability. This paper marries materials- and process-related issues and, could pave the way for test methods for 3D printable mixture qualification.

On the shear thinning of non-Brownian suspensions: Friction or adhesion?

Shear thinning is fundamental to a broad range of particle suspensions, both in nature and in industrial applications. Yet the mechanisms governing it remain unclear. In particular, the distinct, and often competing, roles of the interparticle, particle-fluid interactions and the particle surface morphology need clarity. By using non-Brownian silica particles with different morphologies, surface functional groups and suspending media, here we reveal two different shear thinning mechanisms, controlled either by frictional or adhesion forces between particles. Smooth glass sphere suspensions in a polar medium (glycerol), where particles interact strongly with the solvent, showed no shear thinning even at high volume fractions (φ ≥ 0.5), while rough silica particles, with similar size distribution, induced shear thinning behaviour at φ values of 0.25 and above. The latter is attributed to the increased frictional contacts in the rough and irregular particles. Considering surface irregularity as elastically deformable asperities enabled us to estimate the critical load above which two neighbouring rough particles experience frictional contacts giving rise to shear thinning. In contrast, in a non-polar solvent (mineral oil), with which the particles do not interact strongly, both glass spheres and the rough silicas showed a pronounced shear thinning response and yield stress behaviour at volume fractions as low as 2% v/v. The rheology of these suspensions is dictated by the adhesion forces between the particles that lead to the formation of large agglomerates, which breakdown under increasing shear. The evolution of the sheared suspensions microstructure was captured using an optical shearing cell, which also enabled us to quantify the particle agglomeration characteristics using an aggregation index. To demonstrate the generality of our approach, we modified the surface chemistry of the glass spheres by introducing hydrophobic groups (e.g. a fluorosilane or palmitic acid) to inhibit inter-particle interactions and improve the dispersion of the otherwise inherently hydrophilic glass spheres in mineral oil; as expected, this suppressed the shear thinning behaviour of the suspensions. The present results clearly elucidate alternative design routes to control suspension rheology, whether to promote or suppress shear thinning, offering new insights for manufacturing and applications of complex particle suspensions.

Simulations of Frictional Losses in a Turbulent Blood Flow Using Three Rheological Models

Blood flow rate is a crucial factor in transporting an oxygen and depends on several parameters like heart pressure, blood properties like density and viscosity, frictional loss and diameter and shape of vein. Frictional loss is a main challenge of current engineering. Therefore, simulation of dependence of blood properties on frictional loss is very important. When blood properties are considered the first step is to find proper rheological model. It is well known that human blood demonstrates a yield shear stress. Therefore, the research is focused on simulating frictional losses in a turbulent flow of human blood, which demonstrates a yield stress. Three arbitrarily chosen rheological models were considered, namely Bingham, Casson and Herschel-Bulkley. Governing equations describing turbulent blood flow were developed to axially symmetrical an aorta. The mathematical model constitutes three partial differential equations, namely momentum equation, kinetic energy of turbulence and its dissipation rate. The main objective of the research is examining influence of the yield shear stress on frictional losses in a human blood in an aorta when flow becomes turbulent. Simulation of blood flow confirmed marginal influence of a yield shear stress on frictional losses when flow becomes turbulent. Results of simulations are discussed and final conclusions are stated.

Rheological material functions at yielding

In the present work, we define material functions at yielding in a perspective where elasticity and thixotropy can play an important role. These complex materials need to be characterized with a broader approach than the simple single value of the shear yield stress in a viscometric condition. Special emphasis is given to the distinction between static and dynamic yield stresses along with the distinction of viscometric and extensional yielding. The definition of static properties has no parallel with the usual material functions in nonyielding systems, like polymeric liquids, for example, where the words viscometric and extensional have a clear kinematic representation. Instead, static properties have to be measured by means of a stress state, since different stress states can be achieved where no motion takes place. We introduce the definition of material functions at yielding by specifying the yield stress tensor, an entity recently introduced by Thompson et al. [J. Nonnewton. Fluid Mech. 261, 211–219 (2018)], relative to a particular state. In this regard, we define the material functions at yielding as the components of the static and dynamic yield stress tensors in viscometric, in uniaxial extension, in biaxial extension, and in planar extension conditions.