Dependence Of Shear Stress Research Articles

Predicting the Tensile Behavior of Ti-6.6Al-3.3Mo-1.8Zr-0.29Si Alloy via the Temperature-Dependent Crystal Plasticity Method.

Uniaxial tensile flow properties of a duplex Ti-6.6Al-3.3Mo-1.8Zr-0.29Si alloy in a temperature range from 213 K to 573 K are investigated through crystal plasticity modelling. Experimental results indicate that the initial yield stress of the alloy decreases as the temperature increases, while its work-hardening behavior displays temperature insensitivity. Considering such properties of the alloy, the dependence of the initial critical resolved shear stress (CRSS) on temperature is taken into account in the polycrystal plasticity modelling. Good coincidence is obtained between modelling and the experimental results. The determined values of CRSS for slip systems are comparable to the published data. The proposed polycrystalline model provides an alternative method for better understanding the microstructure–property relationship of α + β titanium alloys at different temperatures in the future.

Magnetorheology in saturating fields.

Understanding magnetorheology in saturating fields is crucial for success in high torque applications. In this paper we use numerical computations, analytical developments, and experimental data (using a double-gap magnetocell) to study the saturation behavior of model magnetorheological fluids for different particle loadings. Numerical calculations demonstrate a nonlinear dependence of both shear and normal stresses with particle concentration in contrast with analytical predictions. These predictions are in very good agreement with numerical calculations at low volume fractions when the interchain interactions can be safely neglected. Numerical calculations for the (yield) shear stress overestimate experimental data for small and medium concentrations. However, a reasonably good qualitative agreement is found for the larger particle loadings. Normal stresses are extraordinarily sensitive to the particular microstructure; experiments suggest sample dilatation in good agreement with simulations in lattices with a body-centered basis.

Rheological properties of cholesteric liquid crystals as lubricant additives

Rheological properties of Cholesteryl n-valerate, Cholesteryl decanoate and Cholesteryl myristate which are esters of cholesterol have been studied. Phase transition temperatures and rheological parameters such as viscosity, elastic modulus G[Formula: see text], loss modulus G[Formula: see text] as functions of temperature, shear rate and time are investigated. In frequency sweep test, a higher transition crossover region has occurred for Cholesteryl myristate, whereas for Cholesteryl n-valerate a frequency-independent plateau prevailed for both the moduli. The occurrence of blue phase in Cholesteryl decanoate during temperature sweep measurements is an indication for the rheological support. The results for steady state have informed that cholesteric esters are having non-Newtonian flow behavior in their respective cholesteric phases. The power-law model has explained well the shear rate dependence of shear stress. A few practical applications of these esters as lubricant additives are discussed, too.

A diffusion, oxidation reaction and large viscoelastic deformation coupled model with applications to SiC fiber oxidation

In this paper, we present a continuum-level thermodynamically consistent oxidation model that couples large viscoelastic deformation, diffusion and oxidation reaction. Constitutive equations are derived by means of the free energy inequality. The Eyring model for the shear stress dependence of viscosity is adopted to describe the viscous deformation. Subsequently, this model is applied to study the oxidation processes of SiC fibers. A sharp interface between the oxide and substrate naturally develops and propagates forward during the oxidation process. Furthermore, the stresses at the outer surface change from the initial compressive state to tensile due to the viscous deformation and significant volumetric swelling at the interface, which may explain the surface cracking observed in experiments. Notably, the present model can be conveniently used to simulate the oxidation processes that involve complex geometrical shapes without the need to mark and track the interface artificially.

Anomalous slip of ZrB2 ceramic grains during in-situ micropillar compression up to 500 °C

The anisotropic deformation behaviour of ZrB2 grains of basal and prismatic orientations in a polycrystalline ZrB2 sample was studied during in-situ micropillar compression at room temperature (RT), 350 °C and 500 °C. Micropillars were milled out of large grains by focused ion beam machining; the basal and prismatic orientations were previously identified using electron backscatter diffraction maps. The basal pillars showed brittle behaviour and cracking on the 101¯0 and 21¯1¯0 type prismatic planes that lead to their collapse. For this orientation, the yield/rupture stress ranged between 8 and 14 GPa and it exceeded 12 GPa even at 500 °C. In the prismatic orientation, considerable plasticity was observed, showing a temperature dependent yield stress from 6 to 8 GPa at room temperature to ~2GPa at 500 °C. The activated slip system family was identified as 101¯0112¯3 type for all of the test temperatures (RT, 350 °C and 500 °C). Analysis of the Schmid-factors revealed that the plasticity of the prismatic micropillars is controlled by the temperature dependence of the critical resolved shear stress of the 101¯0112¯3 slip systems. The brittleness of the basal micropillars was influenced by their defect structure (e.g. microcracks) and it was temperature independent due to the absence of slip activation.

Cracking behaviour of fine-grained soils: from laboratory testing to numerical modelling

Many experimental evidences suggest that desiccation cracks in clay initiate as a result of the mobilization of soil tensile strength. However this mechanical approach disregards the cohesionless and effective stress-dependent behaviour of fine-grained soil. On the other hand recent findings in the literature suggest that effective stress-dependent shear failure criteria would be appropriate to explain the mechanisms of desiccation cracking for tensile total stress states. This work aims at assessing the validity of a shear failure criterion to predict the onset of cracking in clay forms exposed to air drying. Clay forms of various geometries were experimentally subjected to non-uniform hydraulic and mechanical boundary conditions. Time and location for crack initiation are monitored using a digital camera. Cracking experiments are then modelled in a hydro-mechanical framework using an effective-stress shear failure criterion. The comparison of simulations with experimental results for both the time and the location of cracking allows assuming that cracking occurs due to failure in shearing.

Impact of non-Schmid stress components present in the yield criterion for bcc metals on the activity of [formula omitted] slip systems

It has been found in a number of computer simulations that the yield criterion for the onset of crystal plasticity of body-centered cubic (bcc) metals generally involves stress components other than the shear stress parallel to the slip direction. This is a consequence of the non-planar cores of 1/2〈111〉 screw dislocations that control the plastic deformation of bcc crystals. The significance of these non-Schmid stress components differs from material to material and thus their contributions to the yield criterion requires either extensive atomistic simulations of isolated 1/2[111] screw dislocations or their estimates from experiments. In this paper, we derive a set of constraints imposed on the parameters of the yield criterion that control the importance of different stress components so that the orientation dependence of the critical resolved shear stress and its dependence on the shear stress perpendicular to the slip direction have trends agreeing with atomistic computer simulations. Using the allowed combinations of these parameters, we identify the primary and secondary {110}〈111〉 slip systems for loadings in tension and compression along three specifically oriented loading axes within the standard stereographic triangle. In this context we show that the origin of the tension-compression asymmetry is not related purely to the well-known twinning-antitwinning asymmetry of the yield stress but to a combination of this asymmetry with the effect of the shear stresses perpendicular to the slip direction. Additionally, we demonstrate that our yield criterion, which is based only on the shear stresses parallel and perpendicular to the slip direction, is fully equivalent to more complex yield criteria that contain explicit dependences on normal stresses perpendicular and parallel to the dislocation line. These additional stress terms are shown to emerge due to projection of the applied stress tensor into an orthogonal basis that does not conform with the three-fold screw symmetry of the 〈111〉 rotation axis implicit in bcc crystal structures.

Stress-dependent shear wave splitting and permeability in fractured porous rock

It is well known that shear wave propagates slower across than parallel to a fracture, and as a result, a travelling shear wave splits into two directions when it encounters a fracture. Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell, which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity. A single fracture was created in the samples using a modified Brazilian split test device, where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length. Based on tilt tests and fracture surface profilometry, the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies. Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch. The effective confining stress was varied from 0.5 MPa to 55 MPa, while the fractures were mismatched by 0 mm, 0.45 mm and 1 mm. The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient (JMC). Shear wave splitting, as measured by the difference in the magnitudes of shear wave velocities parallel (VS1) and perpendicular (VS2) to the fracture, is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa, and decreased and approached zero as the effective stress was increased. Simple models for the stress- and JMC-dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations. The effects of the joint wall compressive strength (JCS), JMC and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response. Finally, a useful relationship between fractured rock permeability and shear wave splitting was found after normalization by using JMC.

High-shear rate rheometry of micro-nanofibrillated cellulose (CMF/CNF) suspensions using rotational rheometer

Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic rheometers, which are found in relative scarcity within research facilities compared to rotational rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out.Graphical abstractSteady shear flow data of CMF/CNF suspension from 0.1 to 30,000 s−1 obtained using rotational rheometer

Evidence of, and a proposed explanation for, bimodal transport states in alluvial rivers

Abstract. Gravel-bedded rivers organize their bank-full channel geometry and grain size such that shear stress is close to the threshold of motion. Sand-bedded rivers, on the other hand, typically maintain bank-full fluid stresses far in excess of threshold, a condition for which there is no satisfactory understanding. A fundamental question arises: are bed-load (gravel-bedded) and suspension (sand-bedded) rivers two distinct equilibrium states, or do alluvial rivers exhibit a continuum of transport regimes as some have recently suggested? We address this question in two ways: (1) reanalysis of global channel geometry datasets, with consideration of the dependence of critical shear stress upon site-specific characteristics (e.g., slope and grain size); and (2) examination of a longitudinal river profile as it transits from gravel to sand bedded. Data reveal that the transport state of alluvial riverbed sediments is bimodal, showing either near-threshold or suspension conditions, and that these regimes correspond to the respective bimodal peaks of gravel and sand that comprise natural riverbed sediments. Sand readily forms near-threshold channels in the laboratory and some field settings, however, indicating that another factor, such as bank cohesion, must be responsible for maintaining suspension channels. We hypothesize that alluvial rivers adjust their geometry to the threshold-limiting bed and bank material, which for gravel-bedded rivers is gravel but for sand-bedded rivers is mud (if present), and present tentative evidence for this idea.

Sorption of Cobalt and Methylene Blue Ions by Montmorillonite-Silica Nanocomposites

Background. Deterioration of ecological state of water resources due to increasing content of inorganic and organic toxicants causes the development of scientific research in the direction of sorption materials synthesis, that have improved sorption capacity and selectivity. One of the promising methods for sorbents’ synthesis is the modification of layered silicates, the use of which is restrained by difficulties in separation of latter from the liquid phase.Objective. The aim of the paper is a synthesis of nanocomposites, based on montmorillonite and sodium silicate, study of structure formation features in such systems and sorption properties of the obtained granular materials in relation to heavy metals and organic dyes.Methods. Research of structure formation features in the initial systems by the methods of rheometry and X-ray phase analysis. Condition investigation for the nanocomposites synthesis. Relationship establishment between composition in the initial systems and sorption properties.Results. The structure formation features in the initial water–montmorillonite–silicate systems are studied, the effect of sodium silicate concentration on the rheological properties of the dispersions is established. The effect of the initial system composition on the porous structure of synthesized materials and their sorption properties to remove the cobalt (II) and methylene blue from aqueous solutions is shown.Conclusions. It was found that the limiting shear stress and plastic viscosity dependence of the montmorillonite–sodium silicate solution system has an extreme character (extremum at 0.1–1 % SiO2 content), which is associated with the transition of coagulation contacts into crystallization contacts due to siloxane bonds formation. It has been experimentally confirmed, that an increase in the content of montmorillonite in the obtained materials improves their sorption capacity (up to 450 μmol/g) to the cobalt (II) and methylene blue removal.

Investigation of Rheological Properties of Poly(Vinyl Butyral) Solutions in Methacrylic Monomers

Rheological feature of casting polymerizable compositions based on the solutions of poly(vinyl butyral), di(1-methacryloxy-3-chloropropoxy-2-)methylphosphonate, and 2-hydroxypropyl methacrylate at various ratios, which manifests itself in a two-element mechanical model involving viscous strain and plastic yielding, has been determined. The viscosity values of the solutions have been determined from the dependences of shear stress on the shear rate in the temperature range of 30–80°C. It has been determined that the solutions with the specified ratio of FOM-II-to-HPMA and the content of high-molecular component represented by poly(vinyl butyral) from 1 to 5 wt % are most processible at 30°C.

Quantitative analysis of {332}〈113〉 twinning in a Ti-15Mo alloy by in situ scanning electron microscopy

We have performed quantitative analysis of {332}〈113〉 twinning in a β-Ti-15Mo (wt.%) alloy by in situ scanning electron microscopy and electron backscattering diffraction (EBSD). Microstructure-twinning relations were evaluated by statistical analysis of the evolving twin structure upon deformation at room temperature. Our analysis reveals that at the early stages of deformation (ε < 1.5 to 2.0%), primary twinning is mainly determined by the applied macroscopic stress resolved on the twin system. Most of the primary twins (~70–80% of the analyzed twins) follow Schmid’s law with respect to the macroscopic stress, and most of the growth twins (~ 85% of the analyzed twins) correspond to the higher stressed variant. In the grain size range studied here (40–120 μm), we find that several twin parameters such as number of twins per grain and number of twins per grain boundary area exhibit grain size dependence. We ascribe these effects to the grain size dependence of twin nucleation stress and apparent critical resolved shear stress for twinning, respectively.

Influence of dynamic flow conditions on adsorbed plasma protein corona and surface-induced thrombus generation on antifouling brushes

The information regarding the nature of protein corona (and its changes) and cell binding on biomaterial surface under dynamic conditions is critical to dissect the mechanism of surface-induced thrombosis. In this manuscript, we investigated the nature of protein corona and blood cell binding in heparinized recalcified human plasma, platelet rich plasma and whole blood on three highly hydrophilic antifouling polymer brushes, (poly(N, N-dimethylacrylamide) (PDMA), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) using an in vitro blood loop model at comparable arterial and venous flow, and static conditions. A fluid dynamics model was used initially to better understand the resulting flow patterns in a vertical channel containing the substrates to arrive at the placement of the substrates within the blood loop. The protein binding on the brush modified substrates was determined using ellipsometry, fluorescence microscopy and the nature of the protein corona was investigated using mass spectrometry based proteomics. The flow elevated fouling on brush coated surface from blood. The extent of plasma protein adsorption and platelet adhesion onto PDMA brush was lower than other surfaces in both static and flow conditions. The profiles of adsorbed protein corona showed strong dependence on the test conditions (static vs. flow), and the chemistry of the polymer brushes. Specially, the PDMA brush under flow conditions was more enriched with coagulation proteins, complement proteins, vitronectin and fibronectin but was less enriched with serum albumin. Apolipoprotein B-100 and complement proteins were the most abundant proteins seen on PMPC and PHPMA surfaces under both flow and static conditions, respectively. Unlike PDMA brush, the flow conditions did not affect the composition of protein corona on PMPC and PHPMA brushes. The nature of the protein corona formed in flow conditions influenced the platelet and red blood cell binding. The dependence of shear stress on platelet adhesion from platelet rich plasma and whole blood highlights the contribution of red blood cells in enhancing platelet adhesion on the surface under high shear condition.

Effect of diamond nanoparticle chains on rheological properties of hydrosol

We have recently shown that the sol-gel transition occurs in hydrosol of detonation nanodiamond (DND) particles with size of 4–5 nm. Here we study properties of the hydrosol. Namely, we study the dependence of dynamic viscosity and shear stress on DND concentrations. Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were used for characterization of the hydrosol structure. Deagglomeration of diamond nanoparticles in preparation of the hydrosol was carrying out without mechanical milling. In contrast with previous studies viscosity was measured by rotational viscometer. The observed effects can be explained by the model, that assumes existence of particle chains connected to each other by electrostatic interaction. Moreover, the potential of this interaction is non-spherically symmetric. Such chains of DND particles are present in hydrosols even at the concentration of about 1 wt%.

FEATURES OF RHEOLOGY OF AGAR-AGAR SOLUTIONS

The article presents the results of experiments on studying of rheological behaviour of dilute solutions of agar-agar. The chosen range of concentration 0,1–0,7% allows to avoid gelation at ambient temperature. Dependence of viscosity and shear stress on concentration, shearing speed and temperature in an interval 25–45 °С is investigated. It was found that the concentration dependence of viscosity severely depends on the shear speed, a nonlinearity is observed that increases with decreasing shear speed. The dependence of the viscosity on the shear speed for concentrations of 0,3–0,7% has a similar but gradually changing type of the asymptotic decrease, whereas for 0,1%, solution dependence linearly grows with increase of shear speed. The interrelation of viscosity and shear stress is studied. Curves for solutions of 0,3–0,7% have a similar type and differ significantly from curves for 0,1% solutions. Moreover, the dependencies are not typical for polymer solutions. The activation energy of viscosity and shear stress is studied. For two temperature intervals: 25–35 and 35–45 °C, there is no correlation and a smooth dependence of the measured parameters on temperature. The activation energy of both viscosity and shear stress not decreases with temperature increase, as one might expect, but increases, for many times. This fact is observed completely individually for the different concentrations. An explanation is proposed for the observed dependences, which is based on the assumption of a structural change in agar-agar solutions, which is caused by changing the concentration of solution and magnitude of the mechanical influence.

Stress bifurcation in large amplitude oscillatory shear of yield stress fluids

Large amplitude oscillation shear has been an important method to investigate the yielding and flow behavior of yield stress materials. However, there are great uncertainties in determination of the yield stress from the shear stress (or shear strain) dependence of the apparent dynamic moduli or the relative harmonic intensity using Fourier transform rheology. The yield stress from these dynamic methods is also inconsistent with the steady shear and transient shear measurements. We propose a new method, namely, stress bifurcation, based on the geometric average of elastic and viscous Lissajous curves to study the yielding transition of different yield stress fluids in large amplitude oscillatory shear flow. The results prove that typical yield stress fluids such as concentrated emulsions, polymer nanocomposites, microgels, and particulate gels all exhibit stress bifurcations, both inter and intra cyclically, in large amplitude oscillatory shear experiments. Such stress bifurcation phenomena between the average stress-strain (or strain rate) curves are independent of the type of input signal, i.e., stress-controlled versus strain-controlled. A start yield stress (strain) (related to strain) and an end yield stress (strain rate) (related to strain rate), instead of a single critical variable, were suggested to characterize yielding transitions. The frequency dependences of critical stresses, critical strain, and critical strain rate determined by the new method were also investigated systematically for the different kinds of yield stress fluids. A visco-elastic-plastic model, the Kelvin-Voigt-Herschel-Bulkley model, was also adopted to understand the stress bifurcation and frequency dependencies of critical variables in large oscillatory shear flow.Large amplitude oscillation shear has been an important method to investigate the yielding and flow behavior of yield stress materials. However, there are great uncertainties in determination of the yield stress from the shear stress (or shear strain) dependence of the apparent dynamic moduli or the relative harmonic intensity using Fourier transform rheology. The yield stress from these dynamic methods is also inconsistent with the steady shear and transient shear measurements. We propose a new method, namely, stress bifurcation, based on the geometric average of elastic and viscous Lissajous curves to study the yielding transition of different yield stress fluids in large amplitude oscillatory shear flow. The results prove that typical yield stress fluids such as concentrated emulsions, polymer nanocomposites, microgels, and particulate gels all exhibit stress bifurcations, both inter and intra cyclically, in large amplitude oscillatory shear experiments. Such stress bifurcation phenomena between the av...

Reologic properties of aqueous solutions of agar and gelatine for confectionery

Experimentally by using the rotational viscometer and the temperature scan method the dependence of shear stress on shear rate were determined and the effective dynamic viscosity of the systems water-0.5% agar (WA), water-2% gelatin (WG) and water-0.5% agar-2.0% gelatin (WAG) in the range of shear rates 17-1021 s-1 and temperature range of 298-323 K were calculated. The obtained experimental flow curves were approximated by the equations of the Ostwald power-law model, the Herschel-Bulkley model, and the Kasson model. It is established that the experimental results with good accuracy can be described by the Herschel-Bulkley equation. The values of the yield shear stress and yield index calculated using this equation made it possible to classify the systems WA and WAG in the temperature range 298-310 K as nonlinear plastic with partial transition to pseudoplastic flow. Analysis of the temperature dependence of viscosity from the viewpoint of the activation theory of viscous flow showed a deviation from linearity of the dependence of the logarithm of viscosity on the inverse temperature with decreasing temperature, which suggests the existence of a sol-gel transition from the standpoint of the structural viscosity. The gelation temperatures thus obtained are reduced in a series of WA-WAG-WG systems. Within the framework of the structural approach, the rheological data were analyzed on the basis of the generalized rheological model of Kasson. The contributions to the viscous flow from the integral characteristics of the associates of macromolecules and individual particles calculated from experimental data during their hydrodynamic interaction allowed us to explain an effect of decreasing of viscosity WA system due to adding of gelatin by ruin of the elements of initial system.

Experimental study of shear strength and failure mechanisms in RC beams scaled along height or length

The paper presents results of laboratory experiments carried out on longitudinally reinforced concrete beams subjected to four-point bending. Beams of separately varying height and length were analyzed to investigate the size effect on nominal strength and post-critical brittleness. Beams were scaled in the height direction in the first test series and in the length direction in the second series. Due to lack of geometrical similarity, different failure mechanisms were exhibited. Load-deflection diagrams and crack paths were registered during experiments. The digital image correlation technique was applied to visualize strain localization on the concrete surface. The crack opening and crack slip displacements were also measured. The beam response was characterized by two non-dimensional parameters ηa = a/D and ηb = b/D defined as the ratios of shear and bending spans to the beam depth D assumed as the size parameter and the reinforcement position parameter ηc = c′/D. Two major failure mechanisms were observed: flexural failure in the central beam zone combined with plastic yielding of the reinforcement and the diagonal shear crack failure in external shear zones. Two distinct modes of shear failure can be specified depending on the dominance of crack opening or crack closure contact zones. Two different effective stresses associated with failure mechanisms were defined to specify the beam strength’s dependence on ηa, ηb, ηc and D. Some analytical formulae specifying the critical shear stress dependence on ηa, ηc and strengths ratio of reinforcement and concrete were presented at the end of paper and compared with experimental data.

Study on the Critical Shear Stress of Cohesive Sediments

Since the measurements of bulk property parameters of cohesive sediments can be done easily, it is useful to relate the critical shear stress of cohesive sediments to some of these parameters. In this paper, data from two experiments are reanalysed and the dependence of the critical shear stress on bulk density, clay solid content and clay volume content is highlighted. The results from Sharif demonstrate the critical shear stress as a function of bulk density and clay solid content, while that from Kothyari and Jain indicate that the critical shear stress depends on both the clay solid content and clay volume content of cohesive sediments in the presence of gravel and air. Moreover, it is concluded a critical clay solid content exists around 18%, beyond which the critical shear stress increases rapidly with the increase of bulk density.