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.

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.

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.

The influence of a drag-reducing surfactant on a turbulent velocity field

1999 ◽  
Vol 388 ◽  
pp. 1-20 ◽  
Author(s):  
MICHAEL D. WARHOLIC ◽  
GAVIN M. SCHMIDT ◽  
THOMAS J. HANRATTY
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Root Mean Square ◽  
Reynolds Shear Stress ◽  
Rectangular Channel ◽  
Streamwise Velocity ◽  
Laser Doppler Velocimeter ◽  
Shear Stresses ◽  
Mean Square ◽  
Velocity Fluctuations

A two-component laser-Doppler velocimeter, with high spatial and temporal resolution, was used to study how the introduction of a drag-reducing surfactant to water changes the fully-developed velocity field in an enclosed rectangular channel. Measurements were made for four different Reynolds numbers, Re = 13300; 19100; 32000, and 49100 (based on the bulk viscosity, the half-height of the channel, and the viscosity of water). For a fixed volumetric flow the pressure drop was reduced by 62 to 76% when compared to a Newtonian flow with an equal wall viscosity. Measurements were made of the mean streamwise velocity, the root mean square of two components of the fluctuating velocity, the Reynolds shear stress and the spectral density function of the fluctuating velocity in the streamwise direction. The Reynolds shear stress is found to be zero over the whole channel and the spectra of the streamwise velocity fluctuations show a sharp cutoff at a critical frequency, fc. The ratio of the cutoff frequency to the root mean square of the streamwise velocity fluctuations is found to be approximately equal to 1 mm−1. The observation of a zero Reynolds shear stress indicates the existence of additional mean shear stresses (or mean transfers of momentum) that are not seen with a Newtonian fluid. Furthermore, the presence of a random fluctuating velocity field suggests a production of turbulence by a mechanism other than that usually found for a fully developed flow. Possible explanations for this behaviour are presented.

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.

Autocovariance functions, root-mean-square-roughness height, and autocovariance length for rough deposits of copper, silver, and gold

1982 ◽  
Vol 25 (4) ◽  
pp. 2315-2323 ◽  
Author(s):  
G. Rasigni ◽  
F. Varnier ◽  
M. Rasigni ◽  
J. P. Palmari ◽  
A. Llebaria
Keyword(s):  
Root Mean Square ◽  
Roughness Height ◽  
Root Mean Square Roughness ◽  
Mean Square

The Quantification of Microwear on Chipped Stone Tools: Assessing the Effectiveness of Root Mean Square Roughness (Rq)

2008 ◽  
Vol 33 (2) ◽  
pp. 173-189 ◽  
Author(s):  
W. James Stemp ◽  
Ben E. Childs ◽  
Samuel Vionnet ◽  
Christopher A. Brown
Keyword(s):  
Root Mean Square ◽  
Stone Tools ◽  
Root Mean Square Roughness ◽  
Mean Square ◽  
Chipped Stone

Direct numerical simulation of turbulence over systematically varied irregular rough surfaces

2019 ◽  
Vol 862 ◽  
pp. 781-815 ◽  
Author(s):  
Y. Kuwata ◽  
Y. Kawaguchi
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Root Mean Square ◽  
Drag Force ◽  
Rough Surfaces ◽  
Skin Friction Coefficient ◽  
Root Mean Square Roughness ◽  
Mean Square ◽  
Mean Velocity ◽  
Navier Stokes Equation

Lattice Boltzmann direct numerical simulation of turbulent open-channel flows over randomly distributed hemispheres at $Re_{\unicode[STIX]{x1D70F}}=600$ is carried out to reveal the influence of roughness parameters related to a probability density function of rough-surface elevation on turbulence by analysing the spatial and Reynolds- (double-) averaged Navier–Stokes equation. This study specifically concentrates on the influence of the root-mean-square roughness and the skewness, and profiles of turbulence statistics are compared by introducing an effective wall-normal distance defined as a wall-normal integrated plane porosity. The effective distance can completely collapse the total shear stress outside the roughness sublayer, and thus the similarity of the streamwise mean velocity is clearer by introducing the effective distance. In order to examine the influence of the root-mean-square roughness and the skewness on dynamical effects that contribute to an increase in the skin friction coefficient, the triple-integrated double-averaged Navier–Stokes equation is analysed. The main contributors to the skin friction coefficient are found to be turbulence and drag force. The turbulence contribution increases with the root-mean-square roughness and/or the skewness. The drag force contribution, on the other hand, increases in particular with the root-mean-square roughness whereas an increase in the skewness does not increase the drag force contribution because it does not necessarily increase the surface area of the roughness elements. The contribution of the mean velocity dispersion induced by spatial inhomogeneity of the rough surfaces substantially increases with the root-mean-square roughness. A linear correlation is confirmed between the root-mean-square roughness and the equivalent roughness while the equivalent roughness monotonically increases with the skewness. A new correlation function based on the root-mean-square roughness and the skewness is developed with the available experimental and direct numerical simulation data, and it is confirmed that the developed correlation reasonably predicts the equivalent roughness of various types of real rough surfaces.

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