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Showing papers on "Shear stress published in 1990"


Journal ArticleDOI
TL;DR: In this paper, a method for determining the reduced stress tensor with four degrees of freedom (the orientations of the three principal stress axes as well as the ratio of principal stress differences) using fault slip data (or focal mechanisms of earthquakes) is presented.
Abstract: SUMMARY A new method for determining the reduced stress tensor with four degrees of freedom (the orientations of the three principal stress axes as well as the ratio of principal stress differences) using fault slip data (or focal mechanisms of earthquakes) is presented. From a computational point of view, the inversion of fault slip data is made in a direct way by purely analytical means; as a result, the determination process is extremely fast and adaptable on small microcomputers. From a physical point of view, the method aims at simultaneously (i) minimizing the angles between theoretical shear stress and actual slip vector and (ii) having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction. Examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown. The double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear-stria angle.

649 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the factional properties and stability of frictional sliding for simulated fault gouge and found that the sliding occurs at approximately constant shear stress and net compaction from one load/unload cycle to another ceases.
Abstract: This paper presents an investigation of the factional properties and stability of frictional sliding for simulated fault gouge. In these experiments we sheared gouge layers (quartz sand) under saturated drained conditions and at constant normal stress (50–190 MPa) between either rough steel surfaces or Westerly granite surfaces in a triaxial apparatus. Surface roughness (60 to 320 grit) and gouge layer thickness (0–4.0 mm) were varied in the experiments with granite samples. Porosity ϕ was monitored continuously during shear. Our measurements indicate that granular gouge exhibits strain hardening and net compaction for shear strains γ less than 0.5–1.0. For γ > 0.5–1.0, sliding occurs at approximately constant shear stress and net compaction from one load/unload cycle to the next ceases. Dilatancy occurs at 1/3 to 1/2 the shear stress required for sliding and d2ϕ/dγ2 becomes negative at about the peak stress in a given loading cycle, indicating the onset of shear localization. Oblique shear bands appear in the layers at γ = 1.3–1.5. Experiments with an initial gouge layer exhibit velocity strengthening (the coefficient of friction increases with slip velocity), and initially bare granite surfaces exhibit velocity weakening. The magnitude of velocity strengthening varies inversely with normal stress and directly with gouge thickness and surface roughness. In the gouge experiments the dilatancy rate dϕ/dγ also varies with slip rate. Using a simple energy balance to relate volume change and frictional resistance, we find quantitative agreement between the measured change in dilatancy rate and friction following changes in slip rate. This indicates that velocity strengthening within granular gouge is the result of dilatancy. The slip rate dependence of dϕ/dγ increases with gouge thickness and surface roughness, in agreement with the friction data. Our data therefore suggest that slip within unconsolidated granular material, such as some natural fault gouges, is inherently stable. The results thus provide an explanation for (1) the tendency of gouge accumulation to stabilize slip in laboratory samples, and (2) the tendency for aseismic slip within shallow (< 3–5 km) unconsolidated fault gouge and within unconsolidated sediments such as shallow alluvium and accretionary prisms.

550 citations


Journal ArticleDOI
O. H. Yeoh1
TL;DR: In this article, a cubic equation in the invariant (I1−3) was proposed for the characterization of the elastic properties of carbon-black-filled rubber vulcanizates.
Abstract: A novel strain-energy function which is a simple cubic equation in the invariant (I1−3) is proposed for the characterization of the elastic properties of carbon-black-filled rubber vulcanizates. Conceptually, the proposed function is a material model with a shear modulus which varies with deformation. This contrasts with the neo-Hookean and Mooney-Rivlin models which have a constant shear modulus. The variation of shear modulus with deformation is commonly observed with filled rubbers. Initially, the modulus falls with increasing deformation, leading to a flattening of the shear stress/strain curve. At large deformations, the modulus rises again due to finite extensibility of the network, accentuated by the strain amplication effect of the filler. This characteristic behavior of filled rubbers may be described approximately by the proposed strain-energy function by requiring the coefficient C20 to be negative, while the coefficients C10 and C30 are positive. The use of the proposed strain-energy ...

540 citations


Journal ArticleDOI
TL;DR: A review of the different approaches used for modeling multilayered composite shells is given in this article, where the effects of variation in the lamination and geometric parameters of simply supported composite cylinders on the accuracy of the static and vibrational responses predicted by eight different modeling approaches (based on two-dimensional shear deformation theories).
Abstract: A review is made of the different approaches used for modeling multilayered composite shells. Discussion focuses on different approaches for developing two-dimensional shear deformation theories; classification of two-dimensional theories based on introducing plausible displacement, strain and/or stress assumptions in the thickness direction; first-order shear deformation theories based on linear displacement assumptions in the thickness coordinate; and efficient computational strategies for anisotropic composite shells. Extensive numerical results are presented showing the effects of variation in the lamination and geometric parameters of simply supported composite cylinders on the accuracy of the static and vibrational responses predicted by eight different modeling approaches (based on two-dimensional shear deformation theories).

444 citations


Journal ArticleDOI
TL;DR: In this paper, the authors use a three-axis graph with dimensionless measures of mean flow depth, mean flow velocity, and sediment size along the axes to develop the best approximation to the relationships among bed phases produced by flows of water over loose sediments.
Abstract: Data from 39 flume studies that report equilibrium bed configuration as well as water temperature, flow depth, flow velocity, and sediment size are used to develop the best approximation to the relationships among bed phases (ripples, dunes, lower-regime plane bed, upper-regime plane bed, and antidunes) produced by flows of water over loose sediments. We use a three-axis graph with dimensionless measures of mean flow depth, mean flow velocity, and sediment size along the axes. The relationships are presented as a series of depth-velocity sections and velocity-size sections through the dimensionless diagram. Boundaries between stability fields of the bed phases were drawn as smooth surfaces that minimize misplacement of data points. A large subset of the data, for which reliable values of bed shear stress are reported, was used to represent the stability relationships of the bed phases in a graph of dimensionless boundary shear stress against dimensionless sediment size. The graph shows substantial overlapping of the fields for dunes, upper plane bed, and antidunes owing to the decrease in bed shear stress in the transition from dunes to plane bed with increasing flow velocity. The topology of bed-phase boundaries was guided by the relationships shown in the dimensionless depth-velocity-size diagram.

385 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used a simple analytical model of the force balance on individual grains to calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography.
Abstract: The erodibility of a grain on a rough bed is controlled by, among other factors, its relative projection above the mean bed, its exposure relative to upstream grains, and its friction angle. Here we report direct measurements of friction angles, grain projection and exposure, and small-scale topographic structure on a variety of water-worked mixed-grain sediment surfaces. Using a simple analytical model of the force balance on individual grains, we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography. The friction angle, projection, and exposure of single grain sizes vary widely from point to point within a given bed surface; the variability within a single surface often exceeds the difference between the mean values of disparate surfaces. As a result, the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution, rather than a single value. On a given bed, the crtitical shear stress distributions of different grain sizes have similar lower bounds, but above their lower tails they diverge rapidly, with smaller grains having substantially higher median critical shear stresses. Large numbers of fines, trapp.ed within pockets on the bed or shielded by upstream grains, are effectively lost to the flow. Our calculations suggest that critical shear stress, as conventionally measured, is defined by the most erodible grains, entrained during transient shear stress excursions associated with the turbulent flow; this implies a physical basis for the indeterminacy of initial motion. These observations suggest that transport rate/shear stress relationships may be controlled, in part, by the increasing numbers of grains that become available for entrainment as mean shear stress increases. They also suggest that bed textures and grain size distributions may be controlled, within the constraints of an imposed shear stress and sediment supply regime, by the influence of each size fraction on the erodibility of other grain sizes present on the bed.

373 citations


Journal ArticleDOI
TL;DR: The results suggest that fluid flow induced by mechanical stress may be an important mediator of bone remodeling and inhibition of cyclooxygenase by 20 μM ibuprofen completely inhibited the flow‐dependent cAMP response, indicating the cAMP responded is mediated by prostaglandins.
Abstract: Effects of interstitial fluid flow on osteoblasts were investigated. Intracellular cyclic adenosine monophosphate (cAMP) levels were monitored in cultured osteoblasts subjected to shear rates ranging from 10 to 3,500 sec-1. Cyclic AMP levels were significantly increased at all shear rates from 1 pmole/mg protein to 10-16 pmole/mg protein. Osteoblasts subjected to a shear rate of 430 sec-1 for 0.5-15 minutes exhibited elevated levels (12-fold) of intracellular cAMP, which were sustained throughout the perfusion period. Osteoblasts were three times more sensitive to flow stimulation than human umbilical vein endothelial cells and baby hamster kidney fibroblasts, which also displayed higher cAMP levels (4-fold) after exposure to flow. To distinguish streaming potential effects from shear stress effects, viscosity was increased 5-fold by addition of neutral dextran to the perfusing medium. Shear stress is a function of viscosity, and streaming potentials are not for a given shear rate. The mechanism of this cellular response to flow was shown to be shear stress dependent. Inhibition of cyclooxygenase by 20 microM ibuprofen completely inhibited the flow-dependent cAMP response, indicating the cAMP response is mediated by prostaglandins. Our results suggest that fluid flow induced by mechanical stress may be an important mediator of bone remodeling.

353 citations


Journal ArticleDOI
TL;DR: In this article, a new criterion is introduced for the onset of shear thickening in a concentrated dispersion, which follows from the assumption that shear forces overrule the interparticle forces.
Abstract: A new criterion is introduced for the onset of shear thickening in a concentrated dispersion. The criterion follows from the assumption that shear thickening occurs when the shear forces overrule the interparticle forces. A force balance at small interparticle distances is used to predict the dependence of this critical shear rate on the volume fraction. It is deduced that the critical shear rate is proportional to the interparticle distance, has a linear dependence on the magnitude of the stabilizing force, an inverse linear dependence on the dispersion medium viscosity, and an inverse linear dependence on the particle radius. The model is confirmed experimentally with viscosity measurements on various electrostatically stabilized dispersions. The validity of the model is also checked with data obtained from the literature. Experiments indicate that polydisperse dispersions exhibit pronounced shear thickening but with a less dramatic increase in viscosity than monodisperse dispersions.

292 citations


Proceedings Article
01 Feb 1990
TL;DR: In this article, a second-order turbulence closure was proposed for the compressible shear layer, which is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and direct numerical simulation of compressible, isotropic turbulence.
Abstract: Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

259 citations


Journal ArticleDOI
TL;DR: In this paper, the authors focus on the rheometric study of a physical gel exhibiting a yield stress and show how the determination of shear rheological properties can be affected by anomalous phenomena such as fracture and slip at the wall.
Abstract: This work particularly focuses on the rheometric study of a physical gel exhibiting a yield stress. The measurements were carried out in a cone—plate configuration using two different types of rheometer working under controlled torque or under controlled velocity. Shear creep, constant shear rate, and stress relaxation tests have been performed. Measurements of apparent viscometric properties were conducted at the same time as observation of the strain field in the sample. Observing the strain field enables us to confirm the reliability of the interpretation of the results and also to estimate the true shear rate in the fluid. It is shown how the determination of shear rheological properties can be affected by anomalous phenomena such as fracture and slip at the wall. The influence of roughness of the tool surfaces and of evaporation shows up. The results presented in this study show how some rheometrical measurements of the yeild stress and the microstructural interpretations given, may be erroneous. Some recommendations are made in order to improve current rheometrical tests and their interpretation. A log—log graph with typical shear stress-shear rate measurements and their corresponding strain fields is given: it should be used as a guideline in yield stress fluids rheometry. In addition it is made clear that visual observation of the sheared sample is a key technique. A protection which completely eliminates evaporation is suggested. It is shown that the measurement of residual stress in stress relaxation tests may be a convenient means of determining the value of the yield stress.

237 citations



Journal ArticleDOI
TL;DR: In this article, the authors describe some turbulence measurements carried out in the SERC Flood Channel Facility at Hydraulics Research Ltd., Wallingford, U.K. The facility represents a large scale model of a river system with floodplains, and is designed to produce fully developed boundary layer flows with transverse shear.
Abstract: The paper describes some turbulence measurements carried out in the SERC Flood Channel Facility at Hydraulics Research Ltd., Wallingford, U.K. The facility represents a large scale model of a river system with floodplains, and is designed to produce fully developed boundary layer flows with transverse shear. This article presents some of the open channel flow data, including measurements of the primary velocity, Ū/u ∗, the distribution of turbulent intensities, u1/u∗ , v1/u∗ , and w1/u∗ , the kinetic energy, k/u2∗ , and the Reynolds stresses τzx and τyx in the region of strong lateral shear induced by transverse variation in depth. Attention is focussed on the non linear nature of the Reynolds stresses in the shear layer, flow structures and the lateral variations in eddy viscosity and local friction factor.

Journal ArticleDOI
TL;DR: In this article, the roughness of mobile alluvial surfaces is estimated by inverting sediment-transport formulas to solve for the local boundary shear stress required to predict the observed sediment flux and size.
Abstract: The resistance to flow in the turbulent rough-flow range depends primarily upon the size, shape, and arrangement of the granular material making up the boundary. We have estimated the hydraulic roughness of mobile alluvial surfaces by inverting sediment-transport formulas to solve for the local boundary shear stress required to predict the observed sediment flux and size. Inserting this shear stress value and a near-bed velocity measurement into the law of the wall yields the roughness scale, \Iz\N\do defined as the height above the bed where velocity goes to zero. If the roughness is related to the coarse fraction of the bedload, such as \ID\N\d8\d4, then \Iz\N\do=0.1\ID\N\d8\d4. This roughness, obtained from mobile, naturally packed, and heterogeneous-in-size beds is three times greater than that predicted by the Nikuradse formula developed from nearly uniform and smoothly-packed surfaces. We detect no variation in roughness with transport stage, implying that the large static and slowly moving grains determine flow resistance and that momentum extraction by saltating grains is minor. Application of this simple roughness algorithm allows convenient and accurate calculation of the local boundary shear stress.

Journal ArticleDOI
TL;DR: The influence of laminar shear stress on cell proliferation was investigated for subconfluent bovine aortic endothelial cell monolayers seeded on either glass or Thermanox and pulsatile shear stressed cells exhibited a similar but more sensitive response.

Journal ArticleDOI
TL;DR: In this paper, the average shear stress at collapse is less than peak strength, with a safety factor based on peak strength of 1·2, assuming that brittle soils are loaded non-uniformly.
Abstract: Progressive failure occurs when brittle soils are loaded non-uniformly. The average shear stress at collapse is less than peak strength. The effect cannot be examined by conventional limit equilibrium stability analysis. The Carsington embankment slipped in 1984, just before it reached full height. The slide was 30 m deep and 500 m long, and instrumentation had been installed and read up to the moment of collapse. The strengths of the soils involved were carefully established, as was the exact geometry of the slip. Limit equilibrium analysis showed that, at collapse, the average shear stress mobilized was less than peak strength, with a safety factor based on peak strength of 1·2. Since the soils involved were brittle, progressive failure was a probable cause of the discrepancy. Finite element analyses were performed in which strain-softening soil properties were assumed. Some of these analyses are reported here. The pre-failure displacements, the collapse height and collapse mechanism were recovered by t...

Journal ArticleDOI
TL;DR: In this article, the authors present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four-parameter stress model, which can be used to illustrate the significance of various inverse strategies.
Abstract: The shear stress direction on a fault plane depends only on four of the six components of the stress tensor. Assuming only that the slip direction marks the shear stress direction on any fault plane (and that stress is homogeneous), it is possible to estimate these four stress parameters from populations of fault planes with known slip directions, as several workers have observed. Different formulations of the problem may yield varying best-fitting stresses and estimates of uncertainty. In the simplest case, no assumptions are made regarding the orientations of fault planes relative to the stress tensor; thus the technique allows for the possibility that the fault planes may be very weak. Here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four-parameter stress model, which can be used to illustrate the significance of various inverse strategies. In particular, this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model: (1) the pole rotation (the angle between the observed and predicted slip direction on the observed fault plane), and (2) the minimum rotation (the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model). By allowing for variation of the fault plane as well as the slip vector, the minimum rotation procedure generally achieves a more stable and (presumably) realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure. In a test case using 17 earthquake focal mechanisms from the YuIi region of eastern Taiwan, separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates. Additional constraints on the stress tensor, such as the effect of friction, can be superimposed on the ones used here.

Journal ArticleDOI
TL;DR: In this article, the suitability of the vane-in-cup geometry as a rheometer geometry was addressed and a numerical simulation of this geometry was conducted for a power-law fluid and the results compared with a similar study for a conventional bob-incup geometry.
Abstract: We have addressed the question of the suitability of the vane‐in‐cup as a rheometer geometry. A numerical simulation of this geometry was conducted for a power‐law fluid and the results compared with a similar study for a conventional bob‐in‐cup geometry. The comparison indicates that for a sufficiently shear‐thinning fluid (of shear‐thinning index less than 0.5) the fluid within the periphery of the vane blades is essentially trapped there and turns with the vane as a solid body. Calculation of the shear stress at the cup wall indicates that this quantity is equal in both geometries for a given rotational rate of the spindle. Thus the torque required to turn the spindle would be the same and identical flow curves would be predicted. This prediction was tested on two fluids thought to possess a yield stress: a 5.5% sodium carboxymethylcellulose (CMC) solution and a 4.2% Veegum PRO clay suspension. Equivalent flow curves were obtained at very low stresses/shear rates but a sudden, catastrophic viscosity loss was found for both fluids with the bob at shear rates which were still quite low. Such a loss was observed with the vane as well, but at much higher shear rates. It is suggested that this phenomenon is a form of apparent slip due to the formation of a thixotropic layer at the bob/vane surface. The much flatter stress profile obtained in the vane geometry is reasoned to postpone the formation of this layer. Rheological data obtained with the vane appear to be a faithful representation of these materials and show the absence of a true yield stress.

Journal ArticleDOI
TL;DR: From the measured deflections, the maximum tangential bending stress in the resins near the adhesive interface was calculated, which provided an estimation for the maximum shear stress values occurring at both ends of the strips.
Abstract: We studied relaxation by hygroscopic expansion of the interfacial polymerization shear stress of bonded resin composites. In the experimental set-up, resin composite-cured-to-glass strips bent due to the polymerization shrinkage. The strips were stored wet or dry. The curvatures of the bent strips were recorded, by the scanning of the glass surfaces with a contact profilometer, periodically over a period of two months. From the measured deflections, we calculated the maximum tangential bending stress in the resins near the adhesive interface, which provided an estimation for the maximum shear stress values occurring at both ends of the strips. In the particular experimental set-up, the shear stresses in Bis-GMA/TEGDMA and urethane dimethacrylate-based resins were either fully relieved or converted into an "expansion stress" by hygroscopic expansion. The hydrophobic tricyclodecane dimethacrylate-based resins showed very little stress relaxation.

Journal ArticleDOI
TL;DR: In this article, the authors studied the local breakdown near a propagating crack-tip during slip failure nucleation and its transition process to unstable rupture under mode II conditions using a rock sample with a simulated fault, which is large compared with the size of the breakdown zone.

Journal ArticleDOI
TL;DR: In this article, the authors measured natural vegetation canopies and threshold friction velocities for soil movement at three arid and semi-arid field sites to evaluate the partitioning of shear stress between that absorbed by the plant canopy and the soil surface (this potentially causing movement of soil particles).
Abstract: Measurements of natural vegetation canopies and of threshold friction velocities for soil movement were made at three arid and semiarid field sites. Threshold friction velocities for the vegetated surface and for bare soil were used to evaluate the partitioning of shear stress between that absorbed by the plant canopies and that absorbed by the soil surface (this potentially causing movement of soil particles). Canopy measurements were used to estimate lateral cover (total frontal-silhouette area per unit ground area), a parameter shown by previous laboratory studies to be a good predictor of shear stress partitioning. The relationship between lateral cover and shear stress partitioning for the field sites agreed with the laboratory results of Gillette and Stockton (1989). Results indicate that the protective influence of vegetative cover against wind erosion can be successfully predicted using simple measurements of vegetation canopy structure.

Journal ArticleDOI
TL;DR: Asymmetrical tool marks typically indicate flows directed offshore as discussed by the authors, where the magnitude of stress is greatly increased in the offshore direction (and decreased in the onshore direction) by superimposition of a steady current with an offshore component of flow.
Abstract: In ancient storm-influenced prograding shoreline sequences, sole marks (mainly tool marks) from hummocky crossstratified storm deposits are commonly oriented normal to paleoshoreline and the trend of paleobathymetric contours in the basin. Asymmetrical tool marks typically indicate flows directed offshore. Several workers have attributed their formation to storm-generated, shallow marine turbidity currents. This interpretation conflicts with observations from modern shelves, where storm-driven circulation generally is geostrophically balanced, and time-averaged bottom currents approximately parallel bathymetric contours and the local shoreline. The resolution of these apparently conflicting observations may lie in the realization that tool marks (and many other small paleoflow indicators) form almost instantly as the result of instantaneous flow conditions very near the bed. Beneath storm-generated flows in the shallow ocean, instantaneous and time-averaged characteristics of the bottom boundary layer generally exhibit little similarity. Storm-generated tool marks are formed by the movement of large tools within the thin (less than 1 m) inner boundary layer resulting from the superimposition of waves and currents. The orientation of the peak instantaneous shear stress moving large tools under such combined flows mainly reflects wave-orbital motions, which typically are normal to shore. The magnitude of stress is greatly increased in the offshore direction (and decreased in the onshore direction) by superimposition of a steady current with an offshore component of flow, but the direction of stress is only slightly affected. In ancient storm-influenced sequences, therefore, shore-normal tool marks generally were not formed by turbidity currents; rather, their orientation is best attributed to shoaling waves approaching the coast at a very high angle. Asymmetrical tool marks are directed offshore due to enhanced shear stress on the offshore stroke of waves superimposed on a geostrophic current with an offshore flow component. Tool marks do not reflect the time-averaged bottom-flow direction; in fact, they provide almost no information concerning steady bottom currents. In contrast, high-angle cross-beds (formed in coarser sediment by the migration of dunes and sandwaves), although relatively rare in offshore storm deposits, generally reveal approximately shore-parallel flows in ancient systems. Cross-beds closely reflect the time-averaged flow direction in the outer boundary layer of a geostrophic current, for three reasons: 1) the net transport direction for sand moving as bed load beneath a combined flow lies between the directions of peak instantaneous shear stress and time-averaged shear stress; 2) large ripples disrupt the thin inner boundary layer; and 3) long time intervals (relative to wave-induced velocity oscillations) are required to form large ripples.

Journal ArticleDOI
TL;DR: In this paper, the free field limit analysis of a homogeneous layer of dry soil excited by uniform horizontal and vertical acceleration components leads to simple equations describing various stages of inertial shear fluidization.
Abstract: Free‐field limit analysis of a homogeneous layer of dry soil excited by uniform horizontal and vertical acceleration components leads to simple equations describing various stages of inertial shear fluidization. Orientations of potential shear flow spread out from the initial slip planes developed at moderate acceleration ratios, less than 0.3, until the general fluidization state is reached, when a broad band of planes are mobilized throughout the layer. In these directions, the layer then behaves as a viscous fluid. For loose saturated soils, it is postulated that initial fluidization will initiate liquefaction, and therefore the free‐field solution for this neutral case may serve as a useful benchmark for estimating liquefaction trigger accelerations. All intermediate stages, both active and passive, from static conditions to general dynamic fluidization are expressed. The solution seems relatively insensitive to boundary conditions, since the free‐field lateral pressures derived do not differ signific...

Journal ArticleDOI
TL;DR: The results of this study show that the fluid state of the plasma membrane is important in determining the integrity of hybridomas when exposed to lethal shear levels and increasing membrane fluidity correlates with increasing shear sensitivity.
Abstract: The role of the plasma membrane fluidity (PMF) on the shear sensitivity of HB-32 hybridomas to laminar fluid shear was investigated. Steady-state fluorescence anisotropy (r(s)) of the cationic fluorescent probe 1-[4-(trimethylamino) phenyl]-6-phenylhexa-1,3,5-triene, was used to evaluate the PMF of whole hybridoma cells. The PMF was manipulated by the addition of the anesthetic benzyl alcohol, by temperature changes and by cholesterol enrichment. The effect of these PMF modifying procedures on the shear sensitivity of HB-32 was assessed by exposing the cells to defined levels of laminar shear stress in a Couette flow device. Conditions that resulted in lower r(s) values (indicating higher PMF) yielded a more fragile cell. Batch cultivations supplemented with the shear protective agent Pluronic(R) F-68 showed higher values of r(s) compared to control experiments during various growth phases, suggesting that the protective mechanism of Pluronic F-68 relies on its ability to decrease the PMF through direct interaction with the plasma membrane. The protective mechanism of serum against turbulent fluid shear is also discussed from analysis of growth and death kinetics of agitated and static cultures at increasing serum levels. The results of this study show that the fluid state of the plasma membrane is important in determining the integrity of hybridomas when exposed to lethal shear levels. It is concluded that increasing membrane fluidity correlates with increasing shear sensitivity.

Journal ArticleDOI
W.J. Jun1, Chang Sun Hong1
TL;DR: In this paper, the effects of width-to-thickness, aspect ratio, number of layers, and stacking sequence on the shapes of the unsymmetric cross-play [0 n /90 n ] T (n = 1,2…) family of laminates were investigated.

Journal ArticleDOI
TL;DR: In this article, the authors used a hybrid finite difference scheme and an iterative method to solve the governing equations of flow and turbulence transport in a rectangular channel near a groyne.
Abstract: The depth-averaged velocity and bottom shear stress distributions in a rectangular channel near a groyne are computed by using a 2-D depth averaged model. The model uses a hybrid finite difference scheme and an iterative method to solve the governing equations of flow and turbulence transport. Due to streamline curvature effects in the region near the groyne tip, a correction factor is incorporated into the \Ik\N=ϵ\N turbulence model that significantly improves the agreement between the computed and experimental data of the velocities and of the streamline pattern compared to previous numerical methods. In this region the bottom shear stress is found to be largely influenced by the 3-D effects. A 3-D correction factor is introduced which considerably improves the computed bottom shear stresses. Sensitivity analysis is made on the \Ik\N=ϵ\N model coefficients and on the correction factors of the streamline curvature and the 3-D effects. The experimental errors in the velocity and bottom shear stress measurements are analyzed. The average errors between the computed and previous experimental results are presented with confidence intervals.

Journal ArticleDOI
TL;DR: The current results indicate that for a given system (material properties mu and nu constant), the stress distribution is a function of the ratio of contact radius to layer thickness (a/h), and while tensile stresses are seen to occur only when a/h is small, tensile strain is observed for all a/H values.
Abstract: The stress distribution in the region of contact between a layered elastic sphere and a layered elastic cavity is determined using an analytical model to stimulate contact of articulating joints. The purpose is to use the solution to analyze the effects of cartilage thickness and stiffness, bone stiffness and joint curvature on the resulting stress field, and investigate the possibility of cracking of the material due to tensile and shear stresses. Vertical cracking of cartilage as well as horizontal splitting at the cartilage-calcified cartilage interface has been observed in osteoarthritic joints. The current results indicate that for a given system (material properties mu and nu constant), the stress distribution is a function of the ratio of contact radius to layer thickness (a/h), and while tensile stresses are seen to occur only when a/h is small, tensile strain is observed for all a/h values. Significant shear stresses are observed at the cartilage-bone interface. Softening of cartilage results in an increase in a/h, and a decrease in maximum normal stress. Cartilage thinning increases a/h and the maximum contact stress, while thickening has the opposite effect. A reduction in the indenting radius reduces a/h and increases the maximum normal stress. Bone softening is seen to have negligible effect on the resulting contact parameters and stress distribution.

Journal ArticleDOI
TL;DR: In this paper, a master curve was shown for the sliding friction properties of the polymer under consideration, and the existence of the master curve for variations in average velocity vs. wall stress, during flow with macroscopic slip at the wall.
Abstract: Polymers, melted at room temperature, have been extruded through capillary dies using either a controlled pressure system or an automatic capillary rheometer in which the rate of flow is controlled. When the polymer is highly entangled, macroscopic slip is observed at the wall. However, flow curves differ: for controlled pressure conditions, slip appears simultaneously with a sudden increase in the rate of flow, an dflow curves exhibit a hysteretic regime. For controlled flow conditions, slip is accompanied by oscillations of the rate of flow and pressure head around a mean value, as a result of polymer compressibility. The succession and evolution of the different flow defects are clearly identified. As the flow regime increases, scratches appear first. Then, beyond a critical value of wall shear stress in the exit region, cracks are formed just at the exit of the capillary die. These cracks are accompanied by the formation of “rings”, which are more easily observed as the molecular weight increases. At high flow rates, when macroscopic slip appears at the wall, the aspect of the extrudate depends on the system used. For controlled pressure conditions, the polymer is ejected in the form of an opaque, irregular jet, where swelling is quasi-non-existent. For controlled flow conditions, cork flow is observed. At higher flow regimes the extrudate becomes chaotic. The existence of a master curve was also shown for variations in average velocity vs. wall stress, during flow with macroscopic slip at the wall. It is important to note that this curve represents the sliding friction properties of the polymer under consideration.

Journal ArticleDOI
TL;DR: In this paper, a similarity solution for the convective-diffusion equation governing the steady-state concentration of the boundary layer in crossflow microfiltration of the particles, under conditions where a thin stagnant layer of particles deposited on the microporous membrane surface provides the controlling resistance to filtration, is presented.

Proceedings ArticleDOI
18 Jun 1990
TL;DR: In this paper, a second-order turbulence closure was proposed for the compressible shear layer, which is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and direct numerical simulation of compressible, isotropic turbulence.
Abstract: Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

Journal ArticleDOI
TL;DR: In this paper, the adiabatic shear bands formed in a hollow AISI 4340 steel cylinder subjected to dynamic expansion by means of an explosive charge placed in its longitudinal axis, were characterized.
Abstract: Adiabatic shear bands, formed in a hollow AISI 4340 steel cylinder subjected to dynamic expansion by means of an explosive charge placed in its longitudinal axis, were characterized. The adiabatic shear bands formed in this quenched and tempered steel were of the classical “transformed” type. Scanning electron microscopy (SEM) of etched surfaces revealed that alignment of the lamellae along the direction of shear seems to be the event that precedes shear localization. The transmission electron microscopy of a “white”-etching shear band having undergone a shear strain of approximately 4 revealed that it containedX (Fe5C2) carbides in a martensitic structure. These carbides were observed to form on (112) internal microtwins. Grains could not be resolved inside of the shear band, but they could be observed in the surrounding matrix material. A traverse of the shear band was made, and there existed no definite boundary between the matrix and the shear band. No evidence of a transformation to austenite was observed. Heat transfer calculations were conducted to help explain the features observed inside of the shear band. It is concluded that the “white”-etching bands, commonly referred to in the literature as “transformed” bands, do not exhibit a transformation at values of shear strain of up to 4. The enhanced reflectivity is an etching artifact and is possibly due to microstructural changes, a very small grain size, and carbide redissolution in the bands.