We discuss the stick-slip motion of an elastic block sliding along a rigid substrate. We argue that for a given external shear stress this system shows a discontinuous nonequilibrium transition from a uniform stick state to uniform sliding at some critical stress which is nothing but the Griffith threshold for crack propagation. An inhomogeneous mode of sliding occurs when the driving velocity ...

Understanding how grain and powder lubrication affect rock friction and fracture dilation, and how microscopic fractures develop according to fault activation may directly improve our capabilities in exploration and stimulation of oil and gas reservoirs. Using a novel rotary shear testing apparatus specifically designed and assembled to conduct experiments inside an X-ray micro computed tomogra...

Based on focused ion beam and shear friction apparatus data, the multi-resolutions (0.2 nm–5 μm) volume roughness & asperity contact (VR & AC) three-dimensional structure on principle slip surface interface-surface (PSS-IS) is measured on high performance computational platform; and physical plastic-creep friction model is established by using hybrid hyper-singular integral equation & lattice B...

We demonstrate that friction is not always an exact number. In a simple lubricated system (atomically smooth mica separated by molecularly thin films of squalane), sinusoidal shear forces were applied for millions of cycles. The kinetic friction increased steadily over repetitive cycles and collapsed intermittently to the average value. Individual slip cycles also consisted of a cascade of smal...

The observed flow enhancement in highly confining geometries is believed to be caused by fluid velocity slip at the solid wall surface. Here we present a simple and highly accurate method to predict this slip using equilibrium molecular dynamics. Unlike previous equilibrium molecular dynamics methods, it allows us to directly compute the intrinsic wall-fluid friction coefficient rather than an ...

This report presents the use of a time-marching threedimensional (3-D) compressible Navier-Stokes equation numerical solver with a one-equation turbulence model to simulate the flow fields developed along concave wall surfaces without and with a downstream extension flat wall surface. The 3-D Navier-Stokes numerical solver came from the NASA Glenn-HT code. The one-equation turbulence model was ...

We present a model for the viscous friction in foams and concentrated emulsions, subject to steady shear flow. First, we calculate the energy dissipated due to viscous friction inside the films between two neighboring bubbles or drops, which slide along each other in the flow. Next, from this energy we calculate the macroscopic viscous stress of the sheared foam or emulsion. The model predictio...

[1] Field observations of mature crustal faults suggest that slip in individual events occurs primarily within a thin shear zone, <1–5 mm, within a finely granulated, ultracataclastic fault core. Relevant weakening processes in large crustal events are therefore suggested to be thermal, and to involve the following: (1) thermal pressurization of pore fluid within and adjacent to the deforming f...

[1] Seismic inversions show that earthquake risetimes may be much shorter than the overall rupture duration, indicating that earthquakes may propagate as self‐healing, pulse‐like ruptures. Several mechanisms for producing pulse‐like ruptures have been proposed, including velocity‐weakening friction, interaction of dynamic rupture with fault geometry and local heterogeneity, and effect of bimate...