The average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel. The method was validated in both hydraulically smooth (plexiglass; Reynolds number less than 25,000) and rough regimes (calibrated particles with known roughness). As a first step toward using this method on nat...

for an Invited Paper for the MAR10 Meeting of The American Physical Society Fundamental deformation processes controlling nanoscale friction and wear BERND GOTSMANN, IBM Research Zurich Thermally activated processes are often responsible for the kinetics of deformation and can control tribological performance. In this contribution two such processes are discussed in combination with nanoscale t...

This paper describes the effects of the elastic modulus and sliding velocity on the friction and shear fracture of smooth silanized rigid disks rotating against thin confined films of poly(dimethylsiloxane) (PDMS) elastomers. A rigid glass disk is rotated against thin PDMS films of different thicknesses and moduli bonded to a glass plate at various speeds. While the disk rotates on the PDMS coa...

The molecular mechanism of slip at the interface between polymer melts and weakly attractive smooth surfaces is investigated using molecular dynamics simulations. In agreement with our previous studies on slip flow of shear-thinning fluids, it is shown that the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that at suffic...

-A pressure-shear plate impact experiment is introduced to study time-resolved friction at interfaces subjected to high sliding speeds under relatively high normal pressures. The conditions of slip at the interface are varied by changing the surface roughness of the impacting plates and by varying the applied normal to shear stress ratio. The configuration offers the simplicity of allowing the ...

[1] Earthquake nucleation requires reduction of frictional strength = ( p) with slip or slip rate, where , n, and p are the friction coefficient, normal stress, and fluid pressure, respectively. For rate state at fixed ( p), instabilities can occur when d ss/dv < 0, where ss is the steady state friction and v is slip rate. Shear heating increases p and, if dilatancy and pore pressure diffusion ...

The velocity and stress autocorrelation decay in a dissipative particle dynamics ideal fluid model is analyzed in this paper. The autocorrelation functions are calculated at three different friction parameters and three different time steps using the well-known Groot/Warren algorithm and newer algorithms including self-consistent leap-frog, self-consistent velocity Verlet and Shardlow first and...

Colloid probe friction force microscopy (FFM) has been used to study the lubricity of propylammonium nitrate (PAN) mixed with n-alkanols confined between sliding silica and mica surfaces. Mixtures of PAN with butanol, hexanol, octanol and dodecanol were investigated for various n-alkanol volume fractions to elucidate the effect of n-alkanol hydrocarbon chain length and concentration on shear fo...

We simulate the response of dense granular material to shear. Our simulations use a micromechanical model which includes realistic material models for each deformable grain, and a Coulomb friction model for interactions between grains. We measure the probability density function (PDF) governing the volume distribution of stress for monodisperse and polydisperse samples, circular and polygonal g...

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tau(f)) in the presence of friction-induced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tau(f) at 10 kilometers in depth. Fr...