Micro-scale roughness effects on the friction coefficient of granite surfaces under varying levels of normal stress

2009 ◽  
pp. 145-156 ◽  
Author(s):  
O Biran ◽  
Y Hatzor ◽  
A Ziv
Keyword(s):  
Friction Coefficient ◽  
Normal Stress ◽  
Roughness Effects ◽  
Micro Scale ◽  
Scale Roughness

Friction coefficient and wear mode transition in micro-scale abrasion tests

2011 ◽  
Vol 44 (12) ◽  
pp. 1878-1889 ◽  
Author(s):  
R.C. Cozza ◽  
D.K. Tanaka ◽  
R.M. Souza
Keyword(s):  
Friction Coefficient ◽  
Mode Transition ◽  
Micro Scale ◽  
Wear Mode

Contact of Rough Surfaces in Ankle Implants Under Combined Normal and Twist Loading

2018 ◽  
Vol 1 (4) ◽  
Author(s):  
Mohammad Hodaei ◽  
Kambiz Farhang
Keyword(s):  
Medical Application ◽  
Roughness Effects ◽  
Implant Surface ◽  
Surface Separation ◽  
Lateral Contact ◽  
Medical Issues ◽  
The Mean ◽  
Scale Roughness ◽  
Approximate Equations ◽  
Comprehensive Study

The medical application of implant replacements to remedy the pain in joints has necessitated a comprehensive study of wear due to contact of implant surfaces. Excessive wear can lead to toxicity and other implant associated medical issues such as patient discomfort and decreased mobility. Since implant wear is the result of contact between surfaces of tibia and talus implant, it is important to establish a model that can address implant surface contact mechanics with roughness effects. In this research, a statistical contact model is developed for the interaction of tibia and talus including normal and lateral contact in which surface roughness effects are included. The model accounts for the elastic–plastic interaction of the implant surface with roughness. For this purpose, tibia and talus implants are considered as macroscopic surfaces containing micron-scale roughness. Approximate equations are obtained that relate the contact force to the mean surface separation explicitly. Closed-form equations are obtained for hysteretic energy loss in implant using the approximate equations. Such a function can serve as a very useful tool for implant designers and manufacturers. Natural frequencies of both adduction-abduction and planter-dorsiflexion rotations are obtained using nonlinear vibration analyses.

scholarly journals Confined flow of suspensions modelled by a frictional rheology

2014 ◽  
Vol 759 ◽  
pp. 197-235 ◽  
Author(s):  
Brice Lecampion ◽  
Dmitry I. Garagash
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Predictions ◽  
Dry Granular Flow ◽  
Neutrally Buoyant ◽  
Constitutive Parameters ◽  
Axial Development

AbstractWe investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al. (Phys. Rev. Lett., vol. 107 (18), 2011, 188301). The friction coefficient (shear stress over particle normal stress) and solid volume fraction are taken as functions of the dimensionless viscous number $I$ defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive framework from the flowing regime (bounded by the maximum flowing solid volume fraction) to the fully jammed state (the random close packing limit). We obtain an analytical solution of the fully developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number $I$. The predictions are in excellent agreement with available experimental results for neutrally buoyant suspensions, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We also numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully developed state. The available experimental data are in good agreement with our numerical predictions, when using an accepted phenomenological description of the relative phase slip obtained independently from batch-settlement experiments. The solution of the axial development of the flow notably provides a quantitative estimation of the entrance length effect in a pipe for suspensions when the continuum assumption is valid. Practically, the latter requires that the predicted width of the central (jammed) plug is wider than one particle diameter. A simple analytical expression for development length, inversely proportional to the gap-averaged diffusivity of a frictional suspension, is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.

scholarly journals Does the normal stress parallel to the sliding plane affect the friction of ice upon ice?

2011 ◽  
Vol 57 (205) ◽  
pp. 949-953 ◽  
Author(s):  
Andrew L. Fortt ◽  
Erland M. Schulson
Keyword(s):  
Friction Coefficient ◽  
Normal Stress ◽  
Stress Tensor ◽  
Frictional Resistance ◽  
Biaxial Compression ◽  
Smooth Surfaces ◽  
Loading Direction ◽  
Loading System

AbstractSliding experiments were performed at −10°C on smooth surfaces of freshwater columnar-grained S2 ice sliding against itself at a velocity of 8 × 10−4 m s−1, with the purpose of examining whether normal stress parallel to the sliding plane affects frictional resistance. This component of the stress tensor was varied (0.20–1.83 MPa) using a loading system operated under biaxial compression, by orienting the sliding plane at two different angles, 26° and 64°, with respect to the principal loading direction. Under these conditions, no evidence was found to indicate that the normal stress in the direction of sliding affects the friction coefficient.

An Experimental Study of a Turbulent Wall Jet on Smooth and Transitionally Rough Surfaces

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
N. Rostamy ◽  
D. J. Bergstrom ◽  
D. Sumner ◽  
J. D. Bugg
Keyword(s):  
Friction Coefficient ◽  
Skin Friction ◽  
Laser Doppler Anemometry ◽  
Skin Friction Coefficient ◽  
Wall Jet ◽  
Roughness Effects ◽  
Mean Velocity ◽  
Turbulent Wall ◽  
Inner Region ◽  
Effect Of Surface

The effect of surface roughness on the mean velocity and skin friction characteristics of a plane turbulent wall jet was experimentally investigated using laser Doppler anemometry. The Reynolds number based on the slot height and exit velocity of the jet was approximately Re = 7500. A 36-grit sheet was used to create a transitionally rough flow (44 < ks+ < 70). Measurements were carried out at downstream distances from the jet exit ranging from 20 to 80 slot heights. Both conventional and momentum-viscosity scaling were used to analyze the streamwise evolution of the flow on smooth and rough walls. Three different methods were employed to estimate the friction velocity in the fully developed region of the wall jet, which was then used to calculate the skin friction coefficient. This paper provides new experimental data for the case of a plane wall jet on a transitionally rough surface and uses it to quantify the effects of roughness on the momentum field. The present results indicate that the skin friction coefficient for the rough-wall case compared to a smooth wall increases by as much as 140%. Overall, the study suggests that for the transitionally rough regime considered in the present study, roughness effects are significant but mostly confined to the inner region of the wall jet.

Developing A Rheological Relation for Transient Dense Granular Flows Via Discrete Element Simulation in A Rotating Drum

2020 ◽  
Vol 36 (5) ◽  
pp. 707-719
Author(s):  
C.-C. Lin ◽  
M.-Z. Jiang ◽  
F.-L. Yang
Keyword(s):  
Steady State ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Tangential Stress ◽  
Depth Profile ◽  
Linear Trend ◽  
Wall Friction ◽  
Rotating Drum ◽  
Flow Acceleration ◽  
Degradation Factor

ABSTRACTThis work examines the μ(I) relation that describes the effective friction coefficient μ of a dense granular flow as a function of flow inertial number I, at the center of a rotating drum from its flow onset to steady state using DEM. We want to see how the internal friction coefficient of an accelerating flow may be predicted so that the associated tangential stress can be estimated with the proper knowledge of the normal stress. Under the three investigated drum speeds (3, 4.5 and 6 rpm), the bulk normal stress, σn(y), is found to be a consistent linear depth profile throughout the flow development with a slope degraded from the hydrostatic value, Ph(y), due to lateral wall friction. With the discovery of a non-constant depth-decaying effective wall friction coefficient, we derive analytically a wall-degradation factor K(h) to give σn(y)= K(h)Ph(y). The depth profile of tangential stress, however, varies in time from a concave shape upon acceleration, τa(y), to a more linear trend at the steady state, τss(y). Hence, the μa-Ia profile (with μa=τ/σn) upon flow acceleration offsets from the steady μss(Iss) relation. A pseudo-steady acceleration modification number, ΔI, is proposed to shift the inertial number in the acceleration phase to I* = Ia+ΔI so that the μa-I* data converge to μss(Iss). This finding shall allow us to predict a transient tangential stress by τa(y) = μss(I*)K(y)Ph(y) using the well-accepted knowledge of steady flow rheology, hydrostatic pressure, and the currently developed wall-degradation factor.

A New Concept of the Sliding Compression Test to Independently Investigate the Contact Normal Stress and the Surface Enlargement

2014 ◽  
Vol 939 ◽  
pp. 473-480
Author(s):  
Peter Groche ◽  
Christoph Müller ◽  
Mira Keller
Keyword(s):  
Friction Coefficient ◽  
Normal Stress ◽  
Compression Test ◽  
The Other ◽  
Cold Forging ◽  
Efficient Process ◽  
Highly Efficient ◽  
Other Hand ◽  
Sliding Compression Test

Cold forging is a highly efficient process to produce components. However, the occurring tribological loads are tremendous. Therefore, complex tribological systems are necessary. They can be influenced by numerous factors. Most important are the tribological loads, which can usually be investigated independently. On the other hand, the contact normal stress and the surface enlargement are coupled in tribometer tests. In order to investigate them independently, a new concept for the Sliding Compression Test is presented and verified. This procedure reveals that both values have an influence on the friction coefficient. However, the influence of the surface enlargement is with about two-thirds higher.

scholarly journals Cells spreading on Micro-fabricated Silica Thin film Coatings

2009 ◽  
Vol 15 (S3) ◽  
pp. 77-78 ◽  
Author(s):  
A. Pelaez-Vargas ◽  
N. Ferrell ◽  
M. H. Fernandes ◽  
D. Hansford ◽  
F. J. Monteiro
Keyword(s):  
Fibrous Layer ◽  
Micro Scale ◽  
Film Coatings ◽  
Thin Film Coatings ◽  
Nano Scale ◽  
Complex Process ◽  
Macro Scale ◽  
Silica Thin Film ◽  
Scale Roughness ◽  
Material Interaction

AbstractFrom a biomaterials perspective, it is now understood that success in the osseointegration of a dental implant is conditioned by its “macro”, “micro” and “nano” scale features. Macro-scale roughness is necessary to improve primary stabilization in the post-surgical phase inducing a peri-implant thin fibrous layer. However, the more complex process in the true cell-material interaction is dependent on micro and nano scale phenomena. There is clear evidence that cell adhesion, proliferation, organization and phenotype are modulated at the micro-scale and that protein absorption is fundamentally a process conditioned at nano-scale.

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