Showing papers on "Shear stress published in 1986"
TL;DR: In this article, a simple relationship is proposed to relate the shear modulus of a cohesionless soil to a modulus stiffness coefficient, which is a soil property and depends on the characteristics of the soil, and the effective mean principal stress at any point in the soil.
Abstract: Data are presented concerning the shear modulus and damping ratios of sands and gravelly soils as determined by laboratory and field tests. A simple relationship is proposed to relate the shear modulus of a cohesionless soil to a modulus stiffness coefficient, which is a soil property and depends on the characteristics of the soil, and the effective mean principal stress at any point in the soil. Values for the modulus coefficient at low strains are suggested, and it is shown that these values for sands can be estimated from the standard penetration resistance of the sand. Values for gravels are generally greater than those for sands by factors ranging from 1.35–2.5. Suggestions are also made for determining the variation of shear modulus with shear strain and the damping ratios for both sandy and gravelly soils.
945 citations
TL;DR: In atherosclerotic lesion-prone regions of the vascular system, unsteady blood flow characteristics, rather than the magnitude of wall shear stress per se, may be the major determinant of hemodynamically induced endothelial cell turnover.
Abstract: The effects of hemodynamic forces upon vascular endothelial cell turnover were studied by exposing contact-inhibited confluent cell monolayers to shear stresses of varying amplitude in either laminar or turbulent flow. Laminar shear stresses (range, 8-15 dynes/cm2; 24 hr) induced cell alignment in the direction of flow without initiating the cell cycle. In contrast, turbulent shear stresses as low as 1.5 dynes/cm2 for as short a period as 3 hr stimulated substantial endothelial DNA synthesis in the absence of cell alignment, discernible cell retraction, or cell loss. The results of these in vitro experiments suggest that in atherosclerotic lesion-prone regions of the vascular system, unsteady blood flow characteristics, rather than the magnitude of wall shear stress per se, may be the major determinant of hemodynamically induced endothelial cell turnover.
858 citations
TL;DR: In this article, the effects of two energy loss mechanisms on viscosity, stress, and granular temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady-state shearing are calculated.
Abstract: Employing nonequilibrium molecular‐dynamics methods the effects of two energy loss mechanisms on viscosity, stress, and granular‐temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady‐state shearing are calculated. Energy introduced into the system through forced shearing is dissipated by inelastic normal forces or through frictional sliding during collisions resulting in a natural steady‐state kinetic energy density (granular‐temperature) that depends on the density and shear rate of the assembly and on the friction and inelasticity properties of the disks. The calculations show that both the mean deviatoric particle velocity and the effective viscosity of a system of particles with fixed friction and restitution coefficients increase almost linearly with strain rate. Particles with a velocity‐dependent coefficient of restitution show a less rapid increase in both deviatoric velocity and viscosity as strain rate increases. Particles with highly dissipative interactions result in anisotropicpressure and velocity distributions in the assembly, particularly at low densities. At very high densities the pressure also becomes anisotropic due to high contact forces perpendicular to the shearing direction. The mean rotational velocity of the frictional disks is nearly equal to one‐half the shear rate. The calculated ratio of shear stress to normal stress varies significantly with density while the ratio of shear stress to total pressure shows much less variation. The inclusion of surface friction (and thus particle rotation) decreases shear stress at low density but increases shear stress under steady shearing at higher densities.
831 citations
TL;DR: In this article, structural properties of transitionally rough and fully rough turbulent boundary layers were measured in flows at different roughness Reynolds numbers developing over uniform spheres roughness, and they asymptotically approach fully rough behaviour as Rek increases, and smooth behaviour at low Rek Profiles of other Reynolds-stress tensor components, turbulence kinetic energy, turbulence-kinetic energy production, and the turbulencekinetic-energy dissipation are also given, along with appropriate scaling variables.
Abstract: Structural characteristics of transitionally rough and fully rough turbulent boundary layers are presented. These were measured in flows at different roughness Reynolds numbers developing over uniform spheres roughness. Inner regions of the longitudinal component of normal Reynolds stress profiles and log regions of mean profiles continuously change in the transitionally rough regime, as the roughness Reynolds number, Rek, varies. These properties asymptotically approach fully rough behaviour as Rek increases, and smooth behaviour at low Rek Profiles of other Reynolds-stress tensor components, turbulence kinetic energy, turbulence-kinetic-energy production, and the turbulence-kinetic-energy dissipation are also given, along with appropriate scaling variables. Fully rough, one-dimensional spectra of longitudinal velocity fluctuations from boundary-layer inner regions are similar to smooth-wall results for k1 y > 0.2 when non-dimensionalized using distance from the wall y as the lengthscale, and (τ/ρ)½ as the velocity scale, where τ is local shear stress, ρ is static density, and k1 is one-dimensional wavenumber in the flow direction.
355 citations
TL;DR: In this article, the authors show that the material in the layer is highly porous and is saturated with water at high pore pressure, and they conclude that the layer deforms and that the ice stream probably moves principally by such deformation.
Abstract: Seismic reflection studies recently conducted on ice stream B, part of the marine ice sheet of West Antarctica, show a metres-thick layer immediately beneath the ice in which both compressional (P) and shear (S) wave speeds are very low. These low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure. From this, and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice, we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation.
353 citations
TL;DR: In this paper, the authors reviewed the different aspects of the yield stress phenomenon and tried a synthesis of knowledge and concluded that the choice of observation time or shear rate to use should be related to the characteristic time of the flow process to which the result is to be applied.
Abstract: This paper reviews the different aspects of the yield stress phenomenon and attempts a synthesis of knowledge. Yield stress can be probed using constant shear stress or shear rate. The magnitude of the result depends on the time allowed to determine whether the sample has developed continuous flow or has ceased flowing. It is closely associated with creep, stress growth and thixotropic breakdown and recovery, and the characteristic times of these transient responses play a part in yield stress measurement. In thixotropic fluids, yield stress is a function of structure and hence of time. In simple thixotropy, the yield stress derived from the equilibrium flow curve is the same as that for the fully built-up structure. But in many materials, the static yield stress obtained after prolonged rest is much higher than the dynamic yield stress from the equilibrium flow curve. This is associated with the phenomenon in which the equilibrium flow curve bends upwards as the shear rate is reduced to very low values. The paper also reviews the many methods that can be used to measure yield stress. It is pointed out that the choice of observation time or shear rate to use should be related to the characteristic time of the flow process to which the result is to be applied. Examples discussed are solids suspension capability of fluids, levelling and sagging, pipeline flow and start-up power requirement of mixers.
330 citations
TL;DR: In this article, a series of drained tests was carried out on a dense anisotropic sand using a hollow cylinder torsional shear apparatus, and the experimental results showed that the shear deformation of sand due to the rotation of principal stress axes are not negligible as compared with that due to a shear with fixed principal stresses axes and the effects of inherent anisotropes on the deformation and volume change behavior are considerably large.
270 citations
01 Jan 1986
TL;DR: Knowledge of stress distributions in the arterial wall is important for many reasons, such as: in the study of the propagation of pulse waves, one must know the incremental modulus of the elasticity that changes with the stress level.
Abstract: Knowledge of stress distributions in the arterial wall is important for many reasons. In the study of the propagation of pulse waves, one must know the incremental modulus of the elasticity that changes with the stress level. In the study of circulation control, the action of the vascular smooth muscle, which depends on its local stress level (see review in Fung, 1984), must be evaluated. In the study of atherogenesis, one must know the stress distribution in the vessel wall because the tensile and shear stress can alter the local wall permea-bility and pressure gradient which is the force that drives the fluid in or out of the vessel wall (Chuong and Fung, 1983). Accurate evaluation of stress distributions in the arterial wall is therefore an important step toward a better understanding of various physiological functions and pathological mechanisms associated with the circulatory system.
262 citations
TL;DR: It is shown that the shape index distribution along these stenosed vessels may be correlated with the level of wall shear stress, with more elongated cells occurring in regions of higher shear Stress.
Abstract: The pattern of endothelial geometry at various locations along stenosed dog aortas was examined. This was done to test the hypotheses that the shape of an endothelial cell is related to the local wall shear stress associated with the flowing blood and that alterations in hemodynamics, produced by vascular geometrical changes, influence endothelial cell geometry. Aortic stenosis with a reduction of 71% of the cross-sectional area was produced. The animals were sacrificed 12 weeks later, and the endothelial cell geometry and orientation were studied using the vascular casting technique and a computerized analysis to determine cell area and shape index. The regions of the stenosis examined were those known to experience different hemodynamic conditions. The value of the shape index was found to fall rapidly in the convergent region of the stenosis and to increase suddenly in the divergent region, eventually returning to the prestenotic value at a more distal site. Using a model of a stenosis made from a vascular cast, laser Doppler anemometry was applied to measure velocity profiles and to estimate the local wall shear stress in a stenosed aorta. It is shown that the shape index distribution along these stenosed vessels may be correlated with the level of wall shear stress, with more elongated cells occurring in regions of higher shear stress.
260 citations
TL;DR: The systems described provide tools for assessing the individual roles of shear stress, pressure, and mechanical strain on vascular cell structure and function.
Abstract: Endothelial cells are subjected to fluid mechanical forces which accompany blood flow. These cells become elongated and orient their long axes parallel to the direction of shear stress when the cultured cells are subjected to flow in an in vitro circulatory system. When the substrate is compliant and cyclically deformed, to simulate effects of pressure in the vasculature, the cells elongate an orient perpendicular to the axis of deformation. Cell shape changes are reflected in the alignment of microtubule networks. The systems described provide tools for assessing the individual roles of shear stress, pressure, and mechanical strain on vascular cell structure and function.
254 citations
01 Sep 1986
TL;DR: In this paper, a non-linear Maxwell rheological model based on the Eyring theory of fluid flow was proposed for disc machine traction tests of EHD lubricants at constant mean film temperature, and the model incorporates three fluid properties: shear modulus G, viscosity τ and Eyring stress τ 0.
Abstract: The methods of measuring the rheological properties of EHD lubricants are reviewed, but for pressures in excess of 1.0 GPa there is currently no simple alternative to the disc machine. A technique has been developed which enables disc machine traction tests to be carried out at constant mean film temperature. Isothermal tests provide further evidence for the existence of a limiting shear stress τc at which the fluid shears in the manner of a plastic solid. At stresses below this limit the experimental data are found to be in very good accord with the non-linear Maxwell rheological model based on the Eyring theory of fluid flow proposed by Johnson and Tevaarwerk and by Hirst and Moore. The model incorporates three fluid properties: shear modulus G, viscosity τ and Eyring stress τ0. Disc machine measurements of τ, τ0 and the limiting shear stress τc for three fluids—a mineral oil HVI 650, a synthetic polyphenyl ether 5P4E and a traction fluid Santotrac 50—are presented for a range of pressures (0.6–2.5 GPa)...
TL;DR: In this paper, the longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and Reynold's stresses, assuming stationary wave conditions and straight and parallel bottom contours.
Abstract: Analytic and numerical models for longshore currents generated by obliquely incident random waves am compared with field observations. Five days of observations were selected during which the waves were narrow banded in both frequency and direction, in keeping with model assumptions. The extensive measurements included radiation stress and wave directional spectra in 9 m depth, and a closely spaced array of current and pressure sensors on a line perpendicular to shore. The longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and Reynold's stresses, assuming stationary wave conditions and straight and parallel bottom contours. The spatial variation of wave height, required to determine the gradient of the radiation stress, is modeled using linear random wave theory. Given Hrms in 9 m depth, the model predicts Hrms at shoreward locations with an average error of less than 9%. Using a nonlinear bottom shear stress formulation and the meas...
TL;DR: In this paper, the effects of temperature, molecular weight and its distribution, side chain branching, and the structure of polymers on the elastic behavior of bulk homopolymers were investigated, by using logarithmic plots of first normal stress difference (N1) against shear stress (σ12) and log-scale plots of storage modulus (G′) against loss modulus.
Abstract: The effects of temperature, molecular weight and its distribution, side chain branching, and the structure of polymers on the elastic behavior of bulk homopolymers were investigated, by using logarithmic plots of first normal stress difference (N1) against shear stress (σ12) and logarithmic plots of storage modulus (G′) against loss modulus (G″) For the investigation, we have used data from the literature as well as our recent experimental results, covering a very wide range of temperature and shear stress or loss modulus It has been found that such plots are very weakly sensitive to (or virtually independent of) temperature and to the molecular weight of high molecular weight polymers, but strongly dependent upon the molecular weight distribution and the degree of side chain branching A theoretical interpretation of the observed correlations is presented, using molecular theories
TL;DR: The critical shear stress at which cell viability starts to decrease progressively was found to be in the order of l-4 N m -2 in both cases and special measures in the bioreactor design have to be taken in order to supply sufficient oxygen in the absence of excessive shear.
TL;DR: In this article, the authors consider plane flows of identical, smooth, nearly elastic, circular disks interacting with a boundary formed by attaching halves of similar disks at equal intervals along a flat wall and find that the boundary can either supply fluctuation energy to the flow or absorb it, depending on the relative magnitudes of the rate of working of boundary tractions through the slip velocity and the rate at which energy is dissipated in collisions.
Abstract: We consider plane flows of identical, smooth, nearly elastic, circular disks interacting with a boundary formed by attaching halves of similar disks at equal intervals along a flat wall. The roughness of the boundary is given in terms of the diameters of the two types of disks and the spacing of the wall disks. We suppose that the velocity distribution of the flow disks is Maxwellian and calculate the rates at which momentum and energy are supplied to the flow disks in collisions over a unit length of the boundary. At the boundary we balance these supplies with the stress and the total flux of energy in the flow and obtain boundary conditions on the shear stress, pressure, and flux of fluctuation energy. We find that the boundary can either supply fluctuation energy to the flow or absorb it, depending on the relative magnitudes of the rate of working of the boundary tractions through the slip velocity and the rate at which energy is dissipated in collisions. As an example we solve the boundary-value problem for the steady shearing flow maintained by the relative motion of parallel plates a fixed distance apart. When the dimensions and properties of the flow disks and the boundary are given, the specification of the distance between the plates and their relative velocity determines the slip velocity, the shear stress and pressure necessary to maintain the flow, and the distributions of mean velocity, fluctuation energy, and density.
TL;DR: In this article, an experimental study of the dynamic response of non-rotating, stratified reservoirs to the application of surface shear stresses was performed using two-layered and linear stratifications; a moving belt was used to supply a shear stress to the fluid.
Abstract: An experimental study of the dynamic response of non-rotating, stratified reservoirs to the application of surface shear stresses is presented. The experiments were made using two-layered and linear stratifications; a moving belt was used to supply a shear stress to the fluid. Detailed measurements of the density field show that upwelling occurs at all values of the Wedderburn number, W, rather than only occurring when W < 1. Differences between the two-layer theory and the present observations are attributed to the fact that the experimental stratifications were continuous, rather than layered. Shearflow dispersion is observed to be an important mechanism for distributing the effects of localized upwelling over the entire length of the mixed layer. A model of mixed-layer deepening based on upwelling and shearflow dispersion is presented and is compared to the observations of this and other experimental studies.
TL;DR: In this paper, the effects of sample preparation methods on the cyclic undrained stress-strain behavior of sands were investigated by means of triaxial and torsional shear tests using two kinds of clean sands and one kind of sand including fines, with a wide variation in the sample density.
TL;DR: In this article, the effect of small uniaxial stresses on the sintering of CdO powder compacts was studied using a loading dilatometer, where compacts of two different green densities were sintered at 1123 K and subjected to stresses between 0 and 0.25 MPa.
Abstract: The effect of small uniaxial stresses on the sintering of CdO powder compacts was studied using a loading dilatometer. Compacts of two different green densities were sintered at 1123 K and subjected to stresses between 0 and 0.25 MPa. Densification and creep occur simultaneously, and the effects of these two processes can be separated. Between relative densities of 0.5 and 0.9, the dependence of the uniaxial creep rate on density can be described in terms of a stress intensification factor which depends exponentially on the porosity but is independent of the grain size. Comparison of the densification and creep rates permits definition of the sintering stress, which is found to decrease with increasing density, and verification of the Zener relation. The stress and grain size dependence of the creep rate, and the grain size dependence of the densification rate, support grain-boundary diffusion as the rate-controlling step in both processes.
TL;DR: Although the model is an extreme simplification of the actual thickening process, it shows that the observed results can be the consequence of competing shear-dependent processes.
TL;DR: In this article, a portable device for measuring sediment resuspension has been developed, which consists of a cylindrical chamber inside of which a horizontal grid oscillates vertically and creates turbulence, which penetrates down to the sediment-water interface and causes resumption.
TL;DR: In this paper, the equations of motion are solved for the accelerating internal boundary layer beneath a wake, where the interaction of these flow processes produces a local maximum in the boundary shear stress downstream of a bump, even over an otherwise flat bed.
Abstract: When non‐cohesive sediment is set in motion by a unidirectional flow, waves of sand often result; moreover, these waves typically are asymmetrical with steep lee faces that produce flow separation. Behind each wave, a wake region forms which grows in height and decays in strength with distance downstream, producing a near‐bottom acceleration. The no‐slip condition at the bed, however, requires an internal boundary layer to form beneath the wake region which retards the flow there. The interaction of these flow processes produces a local maximum in the boundary shear stress downstream of a bump, even over an otherwise flat bed. Because the erosion rate is proportional to the stress divergence for bed load and weak suspended load transport, erosion will occur upstream of this point and desposition will occur downstream of it, thus influencing the bottom shape. Herein, the equations of motion are solved for the accelerating internal boundary layer beneath a wake. The resulting velocity and boundary shear str...
TL;DR: In this article, a mixed shear flexible finite element with relaxed continuity was developed for the geometrically linear and nonlinear analysis of laminated anisotropic plates, based on a refined higher-order theory, which satisfies zero transverse shear stress boundary conditions on the top and bottom faces of the plate.
TL;DR: In this article, two-dimensional turbulence measurements in air-water two-phase bubbly flow in a pipe using a dual-sensor hot-film anemometry are presented.
TL;DR: In this paper, the transport equations for the Reynolds stresses are closed by modeling the turbulence and mean strain parts of the pressure-strain-rate correlation, and the model constants are determined from simple relationships deduced from measurements in rectilinear and longitudinally curved shear flows.
Abstract: The transport equations for the Reynolds stresses are closed by modeling the turbulence and mean‐strain parts of the pressure‐strain‐rate correlation. The model constants are determined from simple relationships deduced from measurements in rectilinear and longitudinally curved shear flows. It is found that the effects of complex strain fields are more correctly predicted when the influence of the mean‐strain part is reduced from levels indicated by rapid distortion theory, and the turbulence part is adjusted to conform approximately with the measured rates of return to isotropy. The case of the swirling jet is used to illustrate the improved performance of the model.
TL;DR: In this article, the undrained behavior of saturated sand in monotonically loaded triaxial tests is discussed using steady state concepts, and the relations among various drained and undrained strength envelopes are first examined.
Abstract: The undrained behavior of saturated sand in monotonically loaded triaxial tests is discussed using steady state concepts. The relations among various drained and undrained strength envelopes are first examined. These monotonic loading concepts are then used to explain the effect of static shear stress, τS, on the undrained cyclic triaxial strength of anisotropically consolidated specimens. The effect of τS, is found to depend on whether a specimen is contractive, dilative or partially‐contractive. For contractive specimens, the cyclic strength always increases with increasing τS, if there is stress reversal and if the peak shear stress, τp, is smaller than the steady state shear strength, Sus. This effect of stress reversal on cyclic strength is explained by the larger cyclic strains generated in the extension part of the cycle. However, if τp>Sus, cyclic strength can increase or decrease with increasing τs; if there is no shear stress reversal, the cyclic strength always decreases with increasing τS. For...
TL;DR: In this paper, a flexural torsional buckling theory for circular arches of doubly symmetric cross section is developed and closed form solutions are obtained for simply supported arches subjected to equal and opposite end moments (uniform bending), and for circular rings subjected to uniformly distributed radial loads.
Abstract: A flexural torsional buckling theory for circular arches of doubly symmetric cross section is developed. Non linear expressions for the axial and shear strains are derived and these are substituted into the second variation of the total potential to obtain the buckling equation. Closed form solutions are obtained for simply supported arches subjected to equal and opposite end moments (uniform bending), and to uniformly distributed radial loads (uniform compression), and for circular rings subjected to uniformly distributed radial loads. The results are compared with previous solutions (a).
TL;DR: In this paper, the authors derived an expression for the distribution of the tensile mode stress intensity factor along a slightly curved crack front, to first order accuracy in the deviation of the crack front location from a reference straight line.
Abstract: Recent work (Rice, 1985a) has presented the calculations of the first order variation in an elastic displacement field associated with arbitrary incremental planar advance of the location of the front of a half-plane crack in a loaded elastic full space. That work also indicated the relation of such calculations to a three-dimensional weight function theory for crack analysis and derived an expression for the distribution of the tensile mode stress intensity factor along a slightly curved crack front, to first order accuracy in the deviation of the crack front location from a reference straight line. Here we extend the results on stress intensity factors to the shear modes, solving to similar first order accuracy for the in-plane [Mode 2) and antiplane (Mode 3) shear stress intensity factors along a slightly curved crack front. Implications of results for the configurational stability of a straight crack front are discussed. It is also shown that the concept of line tension, while qualitatively useful in characteriz ing the crack extension force (energy release rate) distribution exerted on a tough heterogeneity along a fracture path as the crack front begins to curve around it, does not agree with the exact first order effect that is derived here.
TL;DR: In this paper, a general expression for the stress tensor is obtained which gives the total stress in terms of the shape of the cells, interfacial tension, the initial cell orientation, and the rate of deformation in the liquid.
Abstract: A two-dimensional model for foams having gas volume fraction approaching unity has been developed. A general expression for the stress tensor is obtained which gives the total stress in terms of the shape of the cells, interfacial tension, the initial cell orientation, and the rate of deformation in the liquid. A formalism for describing cell deformation is also presented. By assuming hexagonal, monodisperse foam cells, we are able to obtain analytic expressions for stresses for small shearing and elongational deformations (below the yield strain) as well as for steady shear flow. For strains below the yield point, the stress-strain relation is independent of initial cell orientation. However, the critical strain varies with orientation, and therefore, the yield stress, τ 0 , is a function of orientation. In steady shear flow, the shear stress has a contribution from the liquid which is proportional to the shear rate. Thus, τ yx = τ 0 − C μ γ . , where C is a constant determined from viscous dissipation in the thin liquid films, μ is the liquid film viscosity, and γ . is the shear rate. The yield stress is directly proportional to the liquid surface tension and inversely proportional to cell size.
TL;DR: In this article, it is shown that a stretching lineation is seen parallel to fold hinges over a range of fold axes orientations of at least 40° in strongly deformed quartz-mica schists from Syros, Greece.