scholarly journals Coupling between a glacier and a soft bed: I. A relation between effective pressure and local shear stress determined from till elasticity

1999 ◽  
Vol 45 (149) ◽  
pp. 31-40 ◽  
Author(s):  
Neal R. Iverson ◽  
Robert W. Baker ◽  
Roger LeB. Hooke ◽  
Brian Hanson ◽  
Peter Jansson
Keyword(s):  
Shear Stress ◽  
Shear Strain ◽  
Water Pressure ◽  
Shear Stresses ◽  
Effective Pressure ◽  
Interface Shear ◽  
Shear Moduli ◽  
Ring Shear ◽  
Local Shear ◽  
Local Shear Stress

AbstractTo predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in the laboratory with a ring-shear device. After accounting for the elastic compliance of the device, these tests yielded shear moduli of about 1000 and 1800 kPa at confining pressures of 85 and 280 kPa, respectively. These values are comparable to those of other granular materials undergoing recoverable shear strains of the same magnitude. The local shear stress on the till, calculated by applying the measured shear moduli to the tilt record, scales with Pe1.7, where Pe is the effective pressure. This relation implies that as Pe decreases at the ice/till interface, shear stresses on the till are reduced and concentrated elsewhere on the bed, perhaps where the till is absent or the glacier is frozen to the bed. When compared with the strength of the till determined from ring-shear tests, this relation also accounts for the lack of permanent deformation at depth in the bed during periods of low Pe and indicates that most basal motion was by sliding or ploughing.

scholarly journals Coupling between a glacier and a soft bed: I. A relation between effective pressure and local shear stress determined from till elasticity

1999 ◽  
Vol 45 (149) ◽  
pp. 31-40 ◽  
Author(s):  
Neal R. Iverson ◽  
Robert W. Baker ◽  
Roger LeB. Hooke ◽  
Brian Hanson ◽  
Peter Jansson
Keyword(s):  
Shear Stress ◽  
Shear Strain ◽  
Water Pressure ◽  
Shear Stresses ◽  
Effective Pressure ◽  
Interface Shear ◽  
Shear Moduli ◽  
Ring Shear ◽  
Local Shear ◽  
Local Shear Stress

AbstractTo predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in the laboratory with a ring-shear device. After accounting for the elastic compliance of the device, these tests yielded shear moduli of about 1000 and 1800 kPa at confining pressures of 85 and 280 kPa, respectively. These values are comparable to those of other granular materials undergoing recoverable shear strains of the same magnitude. The local shear stress on the till, calculated by applying the measured shear moduli to the tilt record, scales withPe1.7, wherePeis the effective pressure. This relation implies that asPedecreases at the ice/till interface, shear stresses on the till are reduced and concentrated elsewhere on the bed, perhaps where the till is absent or the glacier is frozen to the bed. When compared with the strength of the till determined from ring-shear tests, this relation also accounts for the lack of permanent deformation at depth in the bed during periods of lowPeand indicates that most basal motion was by sliding or ploughing.

A Numerical Study of the Contact Mechanics and Sub-Surface Stress Effects Experienced Over a Range of Machined Surface Coatings in Rough Surface Contacts

2003 ◽  
Vol 125 (4) ◽  
pp. 720-730 ◽  
Author(s):  
A. Kadiric ◽  
R. S. Sayles ◽  
Xiao Bo Zhou ◽  
E. Ioannides
Keyword(s):  
Shear Stress ◽  
Root Mean Square ◽  
Surface Coatings ◽  
Root Mean Square Roughness ◽  
Shear Stresses ◽  
Elastic Contact ◽  
Mean Square ◽  
Clear Trend ◽  
Local Shear ◽  
Local Shear Stress

The paper employs a rough-surface numerical elastic contact method designed to analyze Hertzian elastic contact effects of surface coatings. In particular the paper explores the differences in the surface contact mechanics and the resulting sub-surface stresses experienced over a range of differing coating material-properties, thickness, and machined roughness levels in a quantitative manner. The effect of a range of surface roughness properties and in particular root mean square roughness (σ) and correlation length β*, on the magnitude and depth of maximum shear stresses in the layer under individual asperities is investigated. This is done for a hard and stiff, and also for a soft and compliant coating, and for two coating thicknesses in each case. The results suggest that the magnitude of the local shear stress increases with increasing ratio σ/β* approximately linearly. The depth of the maximum local shear stress is found to correlate best with β*, however a further clear trend is observed between this depth and the number of profile peaks. The depth also shows a relation to the ratio σ/β* but the correlation in this case is weaker with significant deviations. Neither the magnitude nor the depth of shear stresses shows any significant trend in relation to the roughness (σ) alone. The tensile stresses at the interface, and the subsequent potential for delamination, are also investigated and found to be significant. Approximate correlation between the magnitude of interface tensile stress and root mean square roughness is achieved, but no clear trend in relation to correlation length is evident.

Influence de la turbulence sur la force tractrice dans les canaux rectangulaires lisses

1984 ◽  
Vol 11 (3) ◽  
pp. 655-662 ◽  
Author(s):  
Karol Rohan ◽  
Gérald Pilon
Keyword(s):  
Shear Stress ◽  
Flow Measurement ◽  
Shear Stresses ◽  
Rectangular Channels ◽  
Maximal Shear Stress ◽  
Local Shear ◽  
The Mean ◽  
The University ◽  
New Procedures ◽  
Local Shear Stress

A specific research program was undertaken at the University of Sherbrooke in order to develop new procedures to determine the mean and the maximal shear stress found by means of velocity distribution measurements. For this purpose, the noninvasive flow measurement technique of laser velocimetry was employed.For smooth rectangular channels, a function between local velocity and local shear stress was developed, which includes nondimensional parameters such as the form factor of the cross section, the slope of the energy grade line, and the Reynolds number. This function can also be employed to estimate the value of maximal instantaneous shear stresses.

Cyclic tests on high-quality undisturbed block samples of soft marine Norwegian clay

2013 ◽  
Vol 50 (4) ◽  
pp. 400-412 ◽  
Author(s):  
T. Wichtmann ◽  
K.H. Andersen ◽  
M.A. Sjursen ◽  
T. Berre
Keyword(s):  
Shear Stress ◽  
Shear Strain ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Cyclic Strength ◽  
Shear Stresses ◽  
Loading Frequency ◽  
Test Results ◽  
High Quality ◽  
Average Shear

The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high-quality undisturbed samples obtained from large blocks of a soft marine Norwegian clay are presented. Several tests with different average shear stresses, shear stress amplitudes, loading frequencies, and sample geometries have been performed on block samples taken from different depths. In tests with small average shear stresses, failure occurred due to large shear strain amplitudes, while large permanent shear strains were observed in tests with higher average shear stresses. Diagrams quantifying the undrained cyclic strength, permanent shear strain, shear strain amplitude, and permanent pore-water pressure dependent on average shear stress, shear stress amplitude, and number of cycles have been developed based on the test results. The undrained cyclic strength was found strongly dependent on loading frequency. Block samples from shallower depth showed a somewhat higher undrained cyclic strength. No influence of the height-to-diameter ratio of the samples (h/d = 1 and 2 were compared) could be found. A qualitative comparison of the test results with data for standard tube samples is provided.

scholarly journals A Monotonic Smeared Truss Model to Predict the Envelope Shear Stress—Shear Strain Curve for Reinforced Concrete Panel Elements under Cyclic Shear

2021 ◽  
Vol 2 (1) ◽  
pp. 174-194
Author(s):  
Luís Bernardo ◽  
Saffana Sadieh
Keyword(s):  
Shear Stress ◽  
Reinforced Concrete ◽  
Shear Strain ◽  
Peak Load ◽  
Strain Curve ◽  
Fiber Reinforced Polymers ◽  
Shear Stresses ◽  
Cyclic Shear ◽  
Concrete Panels ◽  
Truss Model

In previous studies, a smeared truss model based on a refinement of the rotating-angle softened truss model (RA-STM) was proposed to predict the full response of structural concrete panel elements under in-plane monotonic loading. This model, called the “efficient RA-STM procedure”, was validated against the experimental results of reinforced and prestressed concrete panels, steel fiber concrete panels, and reinforced concrete panels externally strengthened with fiber-reinforced polymers. The model incorporates equilibrium and compatibility equations, as well as appropriate smeared constitutive laws of the materials. Besides, it incorporates an efficient algorithm for the calculation procedure to compute the solution points without using the classical trial-and-error technique, providing high numerical efficiency and stability. In this study, the efficient RA-STM procedure is adapted and checked against some experimental data related to reinforced concrete (RC) panels tested under in-plane cyclic shear until failure and found in the literature. Being a monotonic model, the predictions from the model are compared with the experimental envelopes of the hysteretic shear stress–shear strain loops. It is shown that the predictions for the shape (at least until the peak load is reached) and for key shear stresses (namely, cracking, yielding, and maximum shear stresses) of the envelope shear stress–shear strain curves are in reasonably good agreement with the experimental ones. From the obtained results, the efficient RA-STM procedure can be considered as a reliable model to predict some important features of the response of RC panels under cyclic shear, at least for a precheck analysis or predesign.

Experimental analysis of interfacial shear stress and electrical resistance of indium tin oxide-coated polyethylene terephthalate films for a whole folding test

2019 ◽  
Vol 36 (2) ◽  
pp. 130-150 ◽  
Author(s):  
Bor-Jiunn Wen ◽  
Shih-An Huang ◽  
Ting-Yu Tseng
Keyword(s):  
Shear Stress ◽  
Polyethylene Terephthalate ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Electrical Resistance ◽  
Interfacial Shear Stress ◽  
Interfacial Shear ◽  
Shear Stresses ◽  
Interface Shear ◽  
Conductive Substrate

The purpose of this study is to analyze the performance of the flexible conductive substrate by interfacial shear stress. This study performed automatic liquid-crystal modulating common-path interferometry (LMCI) optical inspections on 125-µm polyethylene terephthalate (PET) substrates having indium tin oxide (ITO) coating thicknesses of 80 nm, 160 nm, and 230 nm. The nonlinear characteristic of the stress-optical coefficient of the ITO material is obtained using LMCI. To validate the performance of the flexible conductive substrate, this study has utilized an automatic sliding-folding testing platform (ASTP) for a whole-folding test. Eventually, this study successfully has utilized interface shear stresses to validate the performance of the flexible conductive substrate depended on the different thicknesses of the conductive layers for whole-folding test by using LMCI and ASTP. According to the measurement results, as the folding radii decrease and the ITO thicknesses of ITO-coated PET substrates increase, the changes of interfacial shear stresses increase in compressive direction and the change-rates of electrical resistance of ITO-coated PET substrate also increase. Therefore, the interfacial shear stress measurement and analysis results depicted on flexible conductive substrates provide a validation for improving the manufacturing process and for reducing process residual stresses.

Roughness Influence on Turbulent Flow Through Annular Seals

1994 ◽  
Vol 116 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Victor Lucas ◽  
Sterian Danaila ◽  
Olivier Bonneau ◽  
Jean Freˆne
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Mixing Length ◽  
Local Shear ◽  
Wall Shear ◽  
Local Shear Stress

This paper deals with an analysis of turbulent flow in annular seals with rough surfaces. In this approach, our objectives are to develop a model of turbulence including surface roughness and to quantify the influence of surface roughness on turbulent flow. In this paper, in order to simplify the analysis, the inertial effects are neglected. These effects will be taken into account in a subsequent work. Consequently, this study is based on the solution of Reynolds equation. Turbulent flow is solved using Prandtl’s turbulent model with Van Driest’s mixing length expression. In Van Driest’s model, the mixing length depends on wall shear stress. However there are many numerical problems in evaluating this wall shear stress. Therefore, the goal of this work has been to use the local shear stress in the Van Driest’s model. This derived from the work of Elrod and Ng concerning Reichardt’s mixing length. The mixing length expression is then modified to introduce roughness effects. Then, the momentum equations are solved to evaluate the circumferential and axial velocity distributions as well as the turbulent viscosity μ1 (Boussinesq’s hypothesis) within the film. The coefficients of turbulence kx and kz, occurring in the generalized Reynolds’ equation, are then calculated as functions of the flow parameters. Reynolds’ equation is solved by using a finite centered difference method. Dynamic characteristics are calculated by exciting the system numerically, with displacement and velocity perturbations. The model of Van Driest using local shear stress and function of roughness has been compared (for smooth seals) to the Elrod and Ng theory. Some numerical results of the static and dynamic characteristics of a rough seal (with the same roughness on the rotor as on the stator) are presented. These results show the influence of roughness on the dynamic behavior of the shaft.

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