Dependence Of Shear Stress Research Articles

Influence of Magnetic Field and Temperature on Rheological Behavior of Magnetorheological Gel.

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium.

A finite deformation theory for grain boundary plasticity based on geometrically necessary disconnections

Grain boundary processes such as shear coupling and sliding are a consequence of plastic distortion accompanying grain boundary motion. Atomic scale studies using molecular dynamics (MD) and phase field crystal simulations demonstrate non-unique and stress-dependent shear coupling, a key feature that recently motivated the introduction of disconnections as the primary carriers of grain boundary plasticity. In this work, we develop a diffuse-interface finite deformation theory for grain boundary plasticity based on the notion of geometrically necessary disconnections (GND), with a discrete collection of intrinsic coupling factors, defined by the bicrystallography, as inputs to the model. It is emphasized that disconnection density is not a primary variable of the theory, instead it is the plastic slip rate associated with shear coupling that is a fundamental variable, and the resulting incompatibility is measured by the GND density. As an interesting consequence of this framework, we discover that in the presence of grain rotation, plastic shear that is commonly associated with the glide of disconnections, is insufficient to describe grain boundary plasticity, and it must be augmented with an additional plastic rotation. The disconnections-based continuum model can describe phenomena such as state-dependent shear coupling, mode switching, grain boundary sliding and grain rotation. Using finite elements, we simulate grain boundaries driven by shear and synthetic driving forces in bicrystals under various boundary conditions.

Comparative analysis of rheological properties indicators for thermoplastic melts

The introduction analyzes the state of the issue and substantiates the research relevance. The aim of the work is to determine and comparatively analyze the values of physically normalized indicators of rheological properties of typical representatives of thermoplastic melts. In the methodological part of the work, to ensure the comparability of the results, the physically normalized form of the Ostwald-de-Waele power empirical rheological equation proposed by McKelvey is used. The calculation scheme is based on the transition from an approximating power function with rheologically non-deterministic parameters to two dimensionless rheologically determined complexes characterizing the stress-strain state of a nonlinear-viscous medium. The first dimensionless complex is presented in the form as the ratio of the actual shear rate to a unit normalization base value, and the second is in the form as the ratio of shear stresses acting on the deformable medium to the base (reduced) value of these stresses, which are necessary to overcome viscous resistance at a unit normalization shear rate. A technique is described for determining physically normalized indicators of rheological properties using the thermoplastic melts flow curves available in the scientific and technical literature (dependence of shear stresses on shear rate) based on the processing of these graphical dependencies plotted in double logarithmic coordinates. In the main part of the work, the values of physically normalized indicators of rheological parameters (the reduced index of viscous resistance and the indicator of the rheological nonlinearity of the melt) are determined and presented in the form of tables for widely used types of filled and unfilled thermoplastic polymers. A comparative analysis of these indicators has been carried out. Conclusions are given on the work and it is noted that the results of the research can be used in engineering practice, as well as in the educational process when performing rheological calculations of the processes of processing thermoplastic polymeric materials.

The Effect of the First and Second Stress Invariants (Hydrostatic and Deviatoric Stresses) on the Compressibility Function

Experimental work was carried out to investigate the separate roles of the hydrostatic and deviatoric components of stress tensor (Using the First and the second invariants and ). The results were expressed in term of stress dependent shear compliance and apparent compressibility function in the time temperature region of the test (up to seconds at the region of the relaxation).
 The Compressibility Function showed no significant change, when increasing the hydrostatic stress and keeping the deviatoric stress constant, and by varying and keeping constant the change is about 10 for the stress combination of tension-torsion.
 The volume was found to increase with time when increasing and keeping constant.
 In the case of and the deviatoric stress played the major role. All these effects could be rationalized by the idea of the time dependent free volume. If the free - volume increases with time by increasing this could explain the difference in the effect of and on and explain the creep less than recovery.
 There is no difference between the compressibility function in creep and recovery (to within the experimental scatter of ()).
 A small increase in B was detected with time, the maximum difference between the lowest and highest is .

α-Mg/LPSO (Long-Period Stacking Ordered) phase interfaces as obstacles against dislocation slip in as-cast Mg-Zn-Y alloys

The influence of α-Mg/LPSO (Long-Period Stacking Ordered) phase interfaces on the flow stress of as-cast Mg-Zn-Y alloys was experimentally and numerically evaluated by compressive loading samples with different volume fractions of LPSO phase. The experimental results showed that the flow stresses of Mg-Zn-Y alloys with LPSO volume fractions ranging from 40 to 85% are clearly higher than those of single phase α-Mg or LPSO alloys. Comparison of deformation behavior between Mg-Zn-Y alloys and Mg-Zn-Y-Zr alloys, where Zr effectively decreases grain size of α-Mg phase, showed that the flow stresses of Mg-Zn-Y alloys with 25 and 40% of LPSO phase were insensitive to grain size whereas the flow stress of α-Mg single-phase alloy showed clear grain size dependence. By including the dependence of critical resolved shear stress (CRSS) on the average interface spacing, crystal plasticity analysis successfully reproduces the observed experimental stress-strain behavior, which suggests that α-Mg/LPSO phase interfaces are effective obstacles against dislocation slip in two-phase Mg alloys containing LPSO phase.

Моделирование преодоления препятствий в виде пор дислокациями в вольфраме

Tungsten is widely used as a material capable of withstanding working conditions in nuclear reactors and other extreme conditions. Under the influence of irradiation, such defects as Frenkel pairs, pores, and dislocation loops are formed in the metal. Therefore, the research aimed at studying the interactions of these defects with each other and their influence on the mechanical properties of the metal are relevant. The paper presents the theoretical study based on the molecular dynamics method, the purpose of which is to investigate the mechanism of strain hardening of tungsten associated with the interaction of dislocations and pores. The authors solved this problem using the LAMMPS package, carried out the integration of atoms motion equations by the fourth order Verlet method. The model under the study is a single crystal of a certain [111], [–1–12], [1–10] orientation along the basic X, Y, and Z coordinate axis relatively, in which the slip of edge dislocations in the main slip system of BCC metals and their interaction with pores is considered. The authors studied the influence of a pore size on the shear stress magnitude: the growth of pore diameter is proportional to the stress growth. The dependences of shear stress on the shear strain in the temperature range of 600–1400 K are calculated, whereby the temperature change does not significantly influence the stress value. The study shows that dislocations cut the pores and, upon the repeated interaction with a pore, a lower value of peak shear stress is observed than during the first one. The presence of pores leads to the flow stress increase, and such an effect becomes more evident with the increasing pore diameter. The flow stress increases thrice for pores with a diameter of 6 nm compared to the material without pores. The authors described the mechanism of interaction between the edge dislocations and pores under the influence of shear stress.

Shear stress relaxation through the motion of edge dislocations in Cu and Cu–Ni solid solution: A molecular dynamics and discrete dislocation study

Shear stress relaxation through the motion of multiple edge dislocations in a periodic cell is studied by molecular dynamics and discrete dislocation methods. In both methods, we consider systems with an initial edge dislocation on the parallel slip planes. The initial shear strain is applied to the system along the Burgers vector of the dislocations. The velocity profile for a single edge dislocation fitted from a molecular dynamics (Bryukhanov, 2020) is used as the input to discrete dislocation dynamics. The dependence of shear stress, plastic strain, and plastic strain rate on time are analyzed. We show that when dislocations are sufficiently far from each other, relaxation occurs due to dislocation motion, and dislocation velocity can exceed the anisotropic speed of sound. If the dislocations are closer together, relaxation is due to the growth of stacking faults. We find that the stress at which the stress relaxation mechanism changes decreases with increasing dislocation density. Stress relaxation in a Cu–Ni solid solution occurs faster than in pure Cu due to a higher dislocation velocity in the high-velocity regime. However, the shear stress at which nickel atoms increase the plastic strain rate increases with an increase in dislocation density. The dependence of the relaxation time on the dislocation density obtained in discrete dislocation simulations is approximated using the power law. The elastic interaction between dislocations reduces the exponent of the power law from 1/ρ to approximately 1/ρ0.8 for both pure Cu and Cu–Ni solid solutions.

A FEM-Based Optimization Method for Driving Frequency of Contactless Magnetoelastic Torque Sensors in Steel Shafts.

This paper presents a novel finite element method (FEM) of optimization for driving frequency in magneto-mechanical systems using contactless magnetoelastic torque sensors. The optimization technique is based on the generalization of the axial and shear stress dependence of the magnetic permeability tensor. This generalization creates a new possibility for the determination of the torque dependence of a permeability tensor based on measurements of the axial stress on the magnetization curve. Such a possibility of quantitative description of torque dependence of a magnetic permeability tensor has never before been presented. Results from the FEM-based modeling method were validated against a real magnetoelastic torque sensor. The sensitivity characteristics of the model and the real sensor show a maximum using a driving current of similar frequency. Consequently, the proposed method demonstrates the novel possibility of optimizing magnetoelastic sensors for automotive and industrial applications.

CREEP COMPLIANCE OF VISCOELASTIC MATERIALS AT CONSTANT TEPERATURE

Experiments were carried out to investigate the separate roles of the hydrostatic and deviatoric components of stress tensor (using the first and the second invariant and The results were expressed in term of stress dependent shear compliance in the time temperature region of the tests (up to seconds at of the Relaxation). was found to increase in magnitude with increasing both hydrostatic and deviatoric components of stress. caused a shift in the magnitude of and caused an increase in with time. The difference between the shear compliance in creep and recovery was found to decrease with and increase with . All the different effects mentioned above could be rationalized by the idea of the time dependent free volume. If the free volume increases with time by increasing this could explain the difference in the effect of and on and explain why creep is less than recovery

Dependence of Shear Stress on Shear Rate during a Flow of Structured Suspensions

Dependence of Shear Stress on Shear Rate during a Flow of Structured Suspensions

Can collateral flow index have an influence on restenosis growth dynamics?

Collateral blood vessels have been statistically linked to a higher probability of repeat stenosis, but these data are not conclusive. Therefore, the aim of this research is to study a possible hydrodynamic pathway for stenosed coronary arteries for two scenarios: in absence of collaterals and in presence of collaterals with different collateral flow indices. For this in this study, we utilised an analytical model and a numerical model for studying this pathway. First, we performed an analytical calculation for the arterial bifurcation with a stenosis and a collateral vessel. Then, we carried out a numerical calculation using an existing numerical model for the same topology. Thus, we obtained the data characterizing the dependence of the wall shear stress on the stenosis degree for various Y-topology cases (without collaterals, and with different collateral flow indices). Then, based on the numerical model, we calculated the dependence of the wall shear stress on the stenosis degree for the physiology-based left coronary artery topology (without collaterals, and with different collateral flow indices). Moreover, to choose the stenosis location to study in the model, we used stent placement frequency statistics, based on data accumulated in clinical practice. As a result, analysis of the obtained data showed that for the structures studied in this work, collateral flow index does not affect the dynamics of restenosis. Thereby, the presence of collateral vessels is unlikely to have an influence on restenosis growth dynamics, and the link is likely purely statistical or follows a different pathway.

Pressure dependence of shear stress during high-pressure torsion of the Au–Co alloys in liquid nitrogen

Measurements of the shear stress were carried out during mechanical alloying by high-pressure torsion of gold-cobalt powder mixing under cryogenic temperature at various pressures for the first time. The pressures were about 5, 8, 10 and 12 GPa. The Au–Co system is characterized by restricted solubility and difference in properties of the constituents. It was found that, in compari-son with the data obtained at room torsion temperature, the values of the shear stress are higher both at the stage of the initial intensive growth and subsequently, upon reaching saturation. With an in-crease in pressure of low-temperature mechanical alloying, a corresponding increase in the resistance to shear strain is observed at all stages of processing. In this case, the shape of the curves at each new pressure changes, as does the staging of the strain dependence. This reflects the extreme heter-ogeneity of the structure formation and phase composition processes of the non-equilibrium alloy. The most intense reflections in the X-ray diffractogram correspond to supersaturated fcc solid solu-tion of cobalt based on gold-base matrix. Also as a result of mechanical alloying, the components of the system are evenly distributed on the fracture surface of the alloy.

Formation of -rotation-type kink boundary in Mg–Zn–Y alloy with long-period stacking ordered structure

The dislocation configuration around the <0001>-rotation-type kink bands/boundaries formed in extruded Mg89Zn4Y7 alloys with a long-period stacking ordered structure was investigated by an intragranular misorientation axis analysis and a g•b study. The g•b analysis suggests that the <0001>-rotation-type kink boundary with small tilt angles comprises prismatic <a> edge dislocations. The tendency of kinking with lattice rotation around the <0001> axis to activate at temperatures higher than 673 K can be explained by the temperature dependence of the critical resolved shear stress of prismatic <a> slips. The kink bands arising from the activation of the prismatic <a> slip system are numerically reproduced by a crystal plasticity finite element analysis. Geometrical softening should be significant despite kink-band formation stimulated by the prismatic slip system.

Laboratory modeling of deformation of specimens with discontinuity under direct shear in constant normal stiffness conditions

This study presents tests of specimens with discontinuity made of artificial geomaterial (concrete-sand mixture) having triangular profile of surface roughness under shear loading with the boundary “constant normal stiffness” condition, with three values of normal compressive load: 0.5, 0.9 and 1.2 MPa. The patterns of deformation were determined at each stage of loading diagrams: linear, nonlinear, peak load and residual strength. The empirical dependences of the ultimate shear stress on normal stress were constructed for different values of roughness.

Rheological model of the fine particles viscoplastic suspension

The analysis of the mechanical behaviour of some types of fine particles suspensions is carried out. A rheological model is proposed to describe the shear stress and shear rate dependence, taking into account the appropriate conditions imposed on the model parameters. It is shown that such model can take into account the “solidification” effect manifestation. A variation of generalization of the rheological model for two- and three-dimensional hydrodynamics problems of fine particles suspensions is proposed, and some methodological features for solving such problems are considered.

Depth and strain rate-dependent mechanical response of chondrocytes in reserve zone cartilage subjected to compressive loading.

The role of the growth plate reserve zone is not well understood. It has been proposed to serve as a source of stem cells and to produce morphogens that control the alignment of clones in preparation for the transition into the proliferative zone. We hypothesized that if such a role exists, there are likely to be mechanoregulatory stimuli in cellular response through the depth of the reserve zone. A poroelastic multiscale finite element model of bone/growth-plate/bone was developed for examining the reserve zone cell transient response when compressed to 5% of the cartilage thickness at strain rates of 0.18%/s, 5%/s, 50%/s, and 200%/s. Chondrocyte maximum principal strains, height-, width-, and membrane-strains were found to be highly dependent on reserve zone tissue depth and strain rate. Cell-level strains and fluid transmembrane outflow from the cell were influenced by the permeability of the calcified cartilage between subchondral bone plate and reserve zone and by the applied strain rate. Cell strain levels in the lower reserve zone were less sensitive to epiphyseal permeability than in the upper reserve zone. In contrast, the intracellular fluid pressures were relatively uniform with reserve zone tissue depth and less sensitive to epiphyseal permeability. Fluid shear stress, induced by fluid flow over the cell surface, provided mechanoregulatory signals potentially sufficient to stimulate reserve zone chondrocytes near the subchondral bone plate interface. These results suggest that the strain rate and tissue depth dependence of cell-level strains and cell surface fluid shear stress may provide mechanoregulatory cues in the reserve zone.

Friction Laws for Saturated/Unsaturated Fatty Acid Layers

The presence or absence of unsaturation in the carbon chain of carboxylic acids was examined on the friction response of boundary films according to normal force. Friction laws were established as a function of the normal force at the nanoscale with a molecular tribometer derived from a surface force apparatus. While the shear plane is mainly composed of methyl groups in all the cases investigated, the molecular organization differs within the shear plane, as suggested by the simultaneous film thickness evolution. This gave rise to dissipation modes within the interface, resulting in a wide range of shear stress levels and dependence with contact pressure. The friction laws were discussed, highlighting the combined role of nanometric surface roughness and molecule unsaturation.Graphic Abstract Friction laws for stearic acid ( ), elaidic acid ( ), and oleic acid ( ) boundary layers and schematic diagrams of the corresponding sheared interfaces

Influence of intermediate layer on the strength of freezing of soil with the metal surface of machines at negative temperatures

The development of moist cohesive soils in conditions of negative temperatures leads to a decrease in the productivity of earth-moving machines due to the increase in adhesion and friction. When wet soil and a metal bucket interact, the soil freezes to the sides of the bucket, which leads to a decrease in the useful volume of the bucket and, therefore, to a decrease in the productivity of the machine. The experimental studies have been carried out on the effect of the intermediate layer at the interface between the soil and the working body of the machine, on adhesion. The prophylactic lubricant "Niogrin" was used as an intermediate layer. As a result of processing the obtained experimental data, a regression equation was obtained; the dependence of the soil shear stress on various factors is presented and the influence of external factors on the adhesion of soils at negative temperatures is estimated. The comparison of the obtained dependencies showed that the strength of soil freezing when using a preventive liquid decreases 1.5-2 times.

Biomechanical Characterization of Endothelial Cells Exposed to Shear Stress Using Acoustic Force Spectroscopy.

Characterizing mechanical properties of cells is important for understanding many cellular processes, such as cell movement, shape, and growth, as well as adaptation to changing environments. In this study, we explore the mechanical properties of endothelial cells that form the biological barrier lining blood vessels, whose dysfunction leads to development of many cardiovascular disorders. Stiffness of living endothelial cells was determined by Acoustic Force Spectroscopy (AFS), by pull parallel multiple functionalized microspheres located at the cell-cell periphery. The unique configuration of the acoustic microfluidic channel allowed us to develop a long-term dynamic culture protocol exposing cells to laminar flow for up to 48 h, with shear stresses in the physiological range (i.e., 6 dyn/cm2). Two different Endothelial cells lines, Human Aortic Endothelial Cells (HAECs) and Human Umbilical Vein Endothelial Cells (HUVECs), were investigated to show the potential of this tool to capture the change in cellular mechanical properties during maturation of a confluent endothelial monolayer. Immunofluorescence microscopy was exploited to follow actin filament rearrangement and junction formation over time. For both cell types we found that the application of shear-stress promotes the typical phenotype of a mature endothelium expressing a linear pattern of VE-cadherin at the cell-cell border and actin filament rearrangement along the perimeter of Endothelial cells. A staircase-like sequence of increasing force steps, ranging from 186 pN to 3.5 nN, was then applied in a single measurement revealing the force-dependent apparent stiffness of the membrane cortex in the kPa range. We also found that beads attached to cells cultured under dynamic conditions were harder to displace than cells cultured under static conditions, showing a stiffer membrane cortex at cell periphery. All together these results demonstrate that the AFS can identify changes in cell mechanics based on force measurements of adherent cells under conditions mimicking their native microenvironment, thus revealing the shear stress dependence of the mechanical properties of neighboring endothelial cells.

A novel two-indenter based micro-pump for lab-on-a-chip application: modeling and characterizing flows for a non-Newtonian fluid

Inspired by the feeding mechanisms of a nematode, a novel two-indenter (2I) micro-pump is analyzed theoretically for transport and mixing of a non-Newtonian fluid for the purpose of lab-on-a-chip applications. Considering that the viscous forces dominate the flows in microscopic regime, the concept lubrication theory was adopted to device the two-dimensional flow model of the problem. By approximating the movements of the indenter as a sinusoidal function, the details of the flow were investigated for variations in—frequency of contraction of the first value keeping the second valve at higher occlusion, and occlusion. The study indicates that occlusive nature of the second valve leads to the large pressure barrier which prevents the fluid to enter into the neighboring compartment. Transport occurs as the lumen opens to develop a suction pressure. Pressure barrier is found to be highest for dilatants followed by Newtonian and pseudo-plastics. Shear stress dependency on frequency the contraction of the first value is highest for lower values of flow behavior index. In conclusion, the study provides details connecting the flows resulting from the indentation of the front-end indenter to the frequency of indentation, geometry and rheology of the fluid, thus facilitating optimal design of the micro-pumps.