Showing papers on "Shear stress published in 1972"

A Reynolds stress model of turbulence and its application to thin shear flows

Abstract: The paper provides a model of turbulence which effects closure through approximated transport equations for the Reynolds stress tensor the turbulence energy κ and e. This model has been incorporated in the numerical solution procedure of Patankar & Spalding (1970) and applied to the prediction of a number of boundary-layer flows including examples of flow remote from walls, those developing along one wall and those confined within ducts. Three of the flows are strongly asymmetric with respect to the surface of zero shear stress and here the turbulent shear stress does not vanish where the mean rate of strain goes to zero. In most cases the predicted profiles and other quantities accord with the data within the probable accuracy of the measurements.

The wall region in turbulent shear flow

Abstract: Hot-film measurements in a fully developed channel flow have been made in an attempt to gain more insight into the process of Reynolds stress production. The background for this effort is the observation of a certain sequence of events (deceleration, ejection and sweep) in the wall region of turbulent flows by Corino (1965) and Corino & Brodkey (1969). The instantaneous product signal uv was classified according to the sign of its components u and v, and these classified portions were then averaged to obtain their contributions to the Reynolds stress . The signal was classified into four categories; the two main ones were that with u negative and v positive, which can be associated with the ejection-type motion of Corino & Brodkey (1969), and that with u positive and v negative, associated with the sweep-type motion. It was found that over the wall region investigated, 3·5 [les ] y [les ] 100, these two types of motion give rise to a stress considerably greater than the total Reynolds stress. Two other types of motion, (i) u negative, v negative, corresponding to low-speed fluid deflected towards the wall, and (ii) u positive, v positive, corresponding to high-speed fluid reflected outwards from the wall, were found to account for the ‘excess’ stress produced by the first two categories, which give contributions of opposite sign.The autocorrelations of the classified portions of uv were obtained to determine the relative time scales of these four types of motion. The positive stress producing motions (u 0 and u > 0, v 0, v > 0). It was further surmised that turbulent energy dissipation is associated with the Reynolds stress producing motions, since these result in localized shear regions in which the dissipation is several orders of magnitude greater than the average dissipation at the wall.

Shear modulus and damping in soils: measurement and parameter effects

Abstract: BASED ON NUMEROUS TESTS ON A SPECTRUM OF DISTURBED AND UNDISTURBED SOILS, THE SHEAR MODULUS DECREASES AND THE DAMPING RATIO INCREASES VERY RAPIDLY WITH INCREASING STRAIN AMPLITUDE. THE RATE OF INCREASE OR DECREASE DEPENDS ON MANY PARAMETERS: EFFECTIVE MEAN PRINCIPAL STRESS; DEGREE OF SATURATION; VOID RATIO; AND NUMBER OF CYCLES OF LOADING. AMBIENT STATES OF OCTAHEDRAL SHEAR STRESS, OVERCONSOLIDATION RATIO, EFFECTIVE STRENGTH ENVELOPE, FREQUENCY OF LOADING, AND TIME EFFECTS HAVE A LESS IMPORTANT INFLUENCE ON THESE PROPERTIES. COHESIVE SOILS ARE AFFECTED DIFFERENTLY THAN CLEAN SANDS. THE APPARATUS USED TO MEASURE SHEAR MODULUS AND DAMPING MUST BE CAPABLE OF MAKING ACCURATE MEASUREMENTS AT VERY SMALL SHEARING STRAINS, THE RANGE BEING DEFINED BY PRACTICAL PROBLEMS IN EARTHQUAKE AND FOUNDATION VIBRATIONS. A PSEUDO STATIC SIMPLE SHEAR APPARATUS AND TWO DIFFERENT RESONANT COLUMN APPARATUS WERE USED. /AUTHOR/

Structure of the reynolds stress near the wall

Abstract: Experimental studies of the flow field near the wall in a turbulent boundary layer using hot-wire probes are reported. Measurements of the product uv are studied using the technique of conditional sampling with a large digital computer to single out special events (bursting) when large contributions to turbulent energy and Reynolds stress occur. The criterion used to determine when the product uv is sampled is that the streamwise velocity at the edge of the sublayer should have attained a certain value. With this simple criterion we find that 60% of the contribution to is made during only 55% of the total time.

The Role of Subaqueous Debris Flow in Generating Turbidity Currents

Abstract: Turbidity currents may be generated in the oceans as part of the sequence from landsliding through debris flow to turbidity current flow. Three aspects of this sequence examined here are 1) the transition from landsliding to debris flow, 2) the mechanics of subaqueous debris flow, and 3) the transition from subaqueous debris flow to turbidity-current flow. The transition from landsliding to debris flow, as observed in the subaerial environment, occurs readily if water is incorporated into the landslide debris as it is jostled and remoulded during downslope movement. Remoulding and incorporation of water reduce the strength and increase the fluid behavior of the debris, thereby causing it to flow rather than slide. Incorporation of only a few percent water typically decreases the strength of landslide debris by a factor of two or more; therefore, landslide debris commonly becomes very fluid with incorporation of a small amount of water. The ready availability of water in the marine environment suggests that conditions are favorable for the development of subaqueous debris flows from subaqueous landslides. Debris flow has been modeled as flow of a plastico-viscous substance, which has a yield strength and deforms viscously at stresses greater than the yield strength. The conditions required for movement of a subaqueous debris flow are described in terms of a critical thickness of debris, which varies directly with strength and inversely with submerged trait weight and slope angle. Within a debris flow, viscous shear occurs where shear stress exceeds the shear strength of the debris, but where shear stress is less than shear strength the material is rafted along as a nondeforming plug. Distinct zones of viscous shear and nondeformation exist in a subaqueous debris flow. Transition from subaqueous debris flow to turbidity-current flow involves extensive dilution of debris-flow material, reducing the density from about 2.0 gm/cm3 to about 1.1 gm/cm3. In experiments, subaqueous debris-flow material was mixed with the surrounding water by erosion of material from the front of the flow and ejection of the material into the overlying water to form a dilute turbulent cloud (turbidity current). The amount of mixing, and hence the size of the turbidity current, varied inversely with the strength of the debris. Conditions that cause mixing at the front of a subaqueous debris flow are illustrated by analyzing flow around a half-body, with boundary-layer separation. Turbidity, currents also may be generated from subaqueous debris flows by mixing water directly into the body of the flow, behind the front, although this type of mixing was not observed in experiments. Mixing into the body of the flow can result from flow instability, either by breaking interface waves or by momentum transfer associated with turbulence, but available information suggests that mixing due to instability is inhibited by the presence of clay and coarse granular solids in debris. Mixing by erosion from the front of a debris flow is favored as being a more typical process of generating turbidity currents because this mixing is a natural consequence of debris flowing through water; it requires no special conditions to operate.

Fracture under complex stress — The angled crack problem

Abstract: Experiments are described in which thin plates of polymethylmethacrylate were fractured with cracks set at various angles to an applied uniaxial stress. While there is substantial agreement with previous analytical predictions, it is shown that inclusion of the stress component parallel to the crack can improve the correlation between linear theory and experiment, using a critical stress at a critical distance interpretation of the stress intensity factor criterion.

Shear Modulus and Damping in Soils: Measurement and Parameter Effects (Terzaghi Leture)

Abstract: Based on numerous tests on a spectrum of disturbed and undisturbed soils, the shear modulus decreases and the damping ratio increases very rapidly with increasing strain amplitude. The rate of increase or decrease depends on many parameters: (1) Effective mean principal stress; (2) degree of saturation; (3) void ratio; and (4) number of cycles of loading. Ambient states of octahedral shear stress, overconsolidation ratio, effective strength envelope, frequency of loading, and time effects have a less important influence on these properties. Cohesive soils are affected differently than clean sands. The apparatus used to measure shear modulus and damping must be capable of making accurate measurements at very small shearing strains, the range being defined by practical problems in earthquake and foundation vibrations. A pseudo static simple shear apparatus and two different resonant column apparatus were used.

Shear transfer in reinforced concrete-recent research

Abstract: THE WAY IN WHICH CONCRETE STRENGTH, SHEAR PLANE CHARACTERISTICS, REINFORCEMENT, AND DIRECT STRESS AFFECT THE SHEAR TRANSFER STRENGTH OF REINFORCED CONCRETE IS DEMONSTRATED. FUNDAMENTAL BEHAVIOR OF TEST SPECIMENS UNDER LOAD IS REPORTED, AND HYPOTHESES TO EXPLAIN THE BEHAVIOR ARE DEVELOPED. IT IS CONCLUDED THAT SHEAR-FRICTION PROVISIONS OF ACI 318-71 GIVE A CONSERVATIVE ESTIMATE OF SHEAR-TRANSFER STRENGTH BELOW THE STATED LIMIT OF 800 PSI. A DESIGN EQUATION TO DEVELOP HIGHER SHEAR TRANSFER STRENGTH IS PRESENTED. /JPCI/

Some theoretical considerations of fibre pull-out from an elastic matrix

Abstract: Previous theoretical work on fibre pull-out from an elastic matrix is briefly discussed and its relation to this present work is indicated. The form of the distribution of shear stress and that of load along the fibre length is determined and its dependence on the elastic properties and fibre length is shown. The theory has been developed to account for the debonding of fibres from the matrix. The maximum fibre load necessary to cause complete debonding and subsequent pull-out is determined and the dependence of the maximum shear stress on the effective embedded fibre length is shown to affect the shear strength calculated from a pull-out test.

Detailed studies of frictional sliding of granite and implications for the earthquake mechanism

Abstract: DETAILED LABORATORY MEASUREMENTS HAVE BEEN MADE ON THE FRICTIONAL CHARACTERISTICS OF WESTERLY GRANITE WITH GROUND SURFACES AND TO NORMAL STRESSES OF 1 KB. THESE MEASUREMENTS SHOW THAT FOR THIS TYPE OF SURFACE THERE ARE THREE TYPES OF SLIDING: CONTINUOUSLY STABLE, EPISODIC STABLE, AND STICK- SLIP. ALL THREE OF THESE MODES HAVE ALSO BEEN OBSERVED ON THE SAN ANDREAS FAULT IN CENTRAL CALIFORNIA. IN OUR LABORATORY EXPERIMENTS, THERE IS A TRANSITION FROM FIRST TO THIRD MODE AT FROM 5 TO 15 BARS NORMAL STRESS, ABOVE WHICH STICK-SLIP PREDOMINATES. STICK-SLIP, HOWEVER, IS ALWAYS PRECEDED BY A SMALL AMOUNT OF STABLE SLIP. IF THIS OCCURS ON A LARGE SCALE ON FAULTS, IT MAY BE A PROMISING PREMONITORY EFFECT FOR EARTHQUAKE PREDICTION. LOADING RATE IS FOUND TO INFLUENCE THE FRICTIONAL STRENGTH INVERSELY, WHICH MAY BE AN EXPLANATION FOR STICK-SLIP. STRESS DROPS WERE FOUND TO INCREASE WITH SHEAR STRESS, BUT NOT LINEARLY, SUGGESTING THAT RADIATION EFFICIENCY MAY INCREASE WITH STRESS DROP.

Compaction of Sands by Repeated Shear Straining

Abstract: Fundamental considerations and published data show that shear strain is the primary factor causing compaction of granular materials. New and published data from laboratory simple shear tests demonstrate the compaction behavior of uniformly graded sands in response to repeated cycles of shear strain. The data from this investigation confirm previous conclusions that the rate of compaction increases with shear strain amplitude but is not significantly affected by the normal stress applied. In addition, it is shown that compression followed by dilation occurs during each moderate- to large-size shear strain excursion; however, the net result of each excursion is a finite density increase until a limiting maximum density is reached. Laboratory simple shear and in situ shear strain data provide a basis for predicting density changes during compaction. Predicted density changes are consistent with published data from field studies of static, vibratory and seismic compaction.

Fully developed asymmetric flow in a plane channel

Abstract: The paper presents the results of a detailed experimental examination of fully developed asymmetric flow between parallel planes. The asymmetry was introduced by roughening one of the planes while the other was left smooth; the ratio of the shear stresses at the two surfaces was typically about 4:1.The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows (generated by the smooth and rough surfaces) interact. Measurements have included profiles of all non-zero double and triple velocity correlations; spectra of the same correlations at several positions in the channel; skewness and flatness factors; and lateral two-point space correlations of the streamwise velocity fluctuation.The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from the rough towards the smooth wall region, giving rise, inter alia, to an appreciable separation between the planes of zero shear stress and maximum mean velocity. The profiles of length scales of the larger-scale motion are, in contrast to the turbulent velocity field, nearly symmetric. Moreover, it appears that at high Reynolds numbers the small-scale motion may in many respects be treated as isotropic.

Modifications of the weissenberg rheogoniometer for measurement of transient rheological properties of molten polyethylene under shear. Comparison with tensile data

Abstract: Improvements to the Weissenberg rheogoniometer are necessary in order to measure the transient rheological properties of polymer melts correctly. The improvements reported concern the mechanical design, a new heating system, a new normal force measuring system, and additional equipment for the relaxation test. Reliable short-time results require sufficiently stiff torque and normal force springs, and a small radius and relatively large angles of the cone-and-plate gap. The behavior of the LDPE melt under test is “linear viscoelastic,” if shear rate or total shear are small: The relaxation modulus, the stress growth at the onset of constant shear rate, the stress relaxation after cessation of steady shear flow, and, in addition, dynamic shear data (from an oscillation viscometer) all show consistent results when correlated by means of formulae from the theory of linear viscoelasticity. Shearing in the nonlinear range with constant shear rate leads to pronounced maxima of the shear stress p12 and of the first normal stress difference p11 − p22 which occur at constant total shear, almost independent of shear rate. Comparison of shear and tensile data (from extensional rheometer) confirms the Trouton relation in the linear-viscoelastic case. In the nonlinear case, there is a “work softening” in shear and a “work hardening” in extension.

On the theory of rolling

Abstract: A comprehensive solution to von Karman’s basic equation is developed, with the aid of a digital computer, the linear first-order differential equation being integrated by a fourth-order Runge–Kutta process. An analytical solution for the special case of constant interfacial shear stress т , equal to the yield shear stress k of the material being rolled, is derived and used to test the convergence of the numerical solution. The mixed boundary condition т = μ s or k whichever is smaller is incorporated, and back and front tensions and both elastic arcs of contact are included in all the proposed solutions, as well as variation of the yield stress k through the arc of contact, so that the theory can be applied to both hot and cold rolling situations. Comparisons are made with successively more approximate solutions and with well-known existing theories and it is shown that none of these earlier theories are capable of predicting roll torque with any degree of precision.

A graphical representation of seismic source parameters

Abstract: The seismic source parameters seismic moment M0, source dimension r, shear-stress drop Δσ, effective shear stress σeff, radiated energy Es, and apparent stress can all be expressed in terms of three spectral parameters that specify the far-field shear displacement of J. N. Brune's 1970 seismic source model: Ω0 (the long-period spectral level), f0 (the spectral corner frequency), and e, which controls the high-frequency (f > f0) decay of spectral amplitudes. All the above source parameters can be easily extracted from a log-log plot of Ω0 versus f0 (e when <1 entering as a parameter), but only three of them are independent. The apparent stress is proportional to the effective shear stress, not the average shear stress. The Ω0-f0 diagram is especially convenient for comparisons within a chosen suite of seismic and/or explosive sources. The equation on which the Gutenberg-Richter energy-magnitude (EGR-ML) relation was originally based is cast into an approximate spectral form; EGR can then be easily compared with Es on the Ω0-f0 diagram for an earthquake of any ML. Within the framework of the (Ω0, f0, e) relations, it is a simple matter to construct an earthquake magnitude scale directly related to the radiated energy Es.

Shear Strength of Large Beams

Abstract: This paper considers the problem of the effect of absolute size on the shear strength of reinforced concrete beams. The results of previous tests are compared and a brief description is given of the way in which beams carry shear force, which is consistent with recent data. Tests on a series of 15 beams in which true scale models were used, with a depth range of 150-1000 mm (6-40 in.) are described. The test results indicate that, when beams are modeled correctly, the effect of absolute size is small. In practice it may not always be possible to design beams of the type in which the size effect is insignificant. For these cases, design advice is given.

Naturally cemented sensitive soils

Abstract: Many extremely sensitive or quick clay soils, particularly but not only those found in Canada, show characteristics of natural cementation bonding between particles. These soils include not only the brackish-marine Leda-type clay deposits but also fresh water varved clays, deep marine clays and others. Although the causes of cementation may vary, the mechanical behaviour of these soils is similar. The unique strength characteristic of naturally cemented soils is a yield curve, defined by breakdown of cementation, which is independent of the classical effective stress patterns of yielding or failure for soils. At low stresses the influence of cementation is to increase strength and resistance to deformation. The cementation yield curve can be generalized in sections, a limit at a constant value of mean normal stress intersecting a limit of shear stress or stress difference. This part of the yield curve is often at a constant value of shear stress over a large range of normal stress. Tensile strength is sma...

Conditionally sampled measurements near the outer edge of a turbulent boundary layer

Abstract: The conditional sampling technique is used to measure ensemble averages of the longitudinal and normal velocity fluctuations u and v respectively and of the Reynolds shear stress fluctuations uv both within the turbulent and irrotational regions near the outer edge of a turbulent boundary layer. The measurements are made in both a smooth- and a rough-wall boundary layer under zero-pressure-gradient conditions. The smooth- and rough-wall results are qualitatively similar but the magnitude of the rough-wall averages is higher than that of the smooth- wall averages, corresponding with the higher value of wall shear stress on the rough surface. The maximum shear stress value encountered within a burst represents a significant proportion of the wall shear stress.The statistical properties of the turbulence within the burst are close but not quite identical to the nearly Gaussian properties of the inner region of the boundary layer. During an attempt to distinguish between bursts of different ages or strengths at the time of measurement, it was found that bursts of relatively short duration travel at much the same longitudinal velocity as the local mean U and contribute little to the local shear stress. The longer and less frequent bursts have a mean velocity smaller than U and a maximum shear stress comparable to the shear stress at the wall.

Axisymmetric Vibrations of a Free Finite‐Length Rod

Abstract: The axisymmetric vibrational characteristics of an elastic circular rod of finite length with stress‐free boundaries are analytically determined, and compared to approximate solutions. The solution approach consists of choosing a series of functions which term by term satisfy the governing equations and the boundary conditions on the shear stress. The boundary conditions on the axial and radial stress are satisfied by an orthogonalization procedure. This method yields an infinite eigenvalue matrix, the coefficients of which are transcendental functions of the frequency. It is found that the procedure converges and that sufficient accuracy is achieved, with truncation to a 20×20 eigenvalue matrix. Comparison is made of these results with the Pochhammer‐Chree solutions which do not permit satisfaction of the boundary conditions on the ends of the rod. This comparison shows many similarities, but also some dissimilarities. Comparisons are also made with the lowest mode of the free‐plate solution and the plane stress solution for very short rods, and with the one‐dimensional rod solution for long rods.

In situ shear wave velocity by cross-hole method.

Abstract: The cross-hole seismic survey technique is presented as a means of determining in situ shear wave velocity. By this method the travel time for body waves to travel between two points in a soil mass is measured. Body waves may be either compression or shear waves. Emphasis is placed on identification of the shear wave because it is directly used to calculate the dynamic shear modulus of the soil and can be measured above or below the water table. A general procedure followed in performing the test is described. Typical travel time records of arriving energy are shown and identification of the compression and shear wave arrivals made. Preliminary tests demonstrating the validity and use of the method are presented. Three case studies using the method under various field conditions are also presented.

Shear Stress Measurements at a Dental Porcelain-Gold Bond Interface

Abstract: In this study a method of measuring interfacial shear stresses from the curvatures of bimaterial dental porcelain-gold strips is described Stresses were calculated for different porcelain thicknesses and as a function of temperature The interfacial stresses found ranged from 1,000 psi tensile stress to 3,000 psi compressive stress on the porcelain side of the interface for porcelain thicknesses commonly used in dental restorations