Friction and wear of carbonate rocks under high velocity sliding
BONEH1, 3, Yuval, SAGY2, Amir, and RECHES3, Ze'ev
1
Earth and Planetary Sciences, Washington University, One Brooking Drive, MO 63130.
2 Geological Survey of Israel, 30 Melkhe Israel St., Jerusalem, Israel.
3 School of Geology & Geophysics, University of Oklahoma, Norman, OK 73019.
Under High velocity:
1. Wear-rates are low
2. Wear-rates do NOT depend on normal
stress (in contradiction with Archard
equation, below)
We experimentally analyze the wear and friction of experimental faults
made of three carbonate rocks: Kasota dolomite (KD), Dover limestone
(DL), and dolomite-quartzite pair (KDBQ), and tested a wide range of
normal stress (up to 7 MPa) and up to seismic slip-velocity (1 m/s).
B
DC
G – wear volume; K – material constant
H – hardness; x – slip distance ; σn – normal stress
R
Friction coefficient and Power - density
Rotary Shear Apparatus
TC
UB
The friction coefficient depends on BOTH slip velocity normal stress (fig. below, left).
It correlates best with the power-density (Fig. below, right).
Power Density = Shear stress * Velocity [Work per unit square], namely
𝑚
𝑀𝑊
Three friction regimes are apparent:
𝜏 ∗ 𝑉 = 𝑀𝑃𝑎 ∗
=
2
𝑠
𝑚2
1. High friction coefficient (μ ~ 0.9) under low power-density of < 0.05 MW/m .
2. Low friction coefficient (μ ~ 0.3) under high power-density > 0.4 MW/m2.
3. Transition zone for intermediate power density of 0.05 – 0.4 MW/m2.
B
1.5 mm
Predicted dynamic friction for various velocities
LB
Synthesis: Fault surface evolution
Brittle regime:
Low velocity and high
normal stress =
High wear-rate, high
friction, and gouge
covered surface.
We analyze here the wear-rate and friction
coefficient during the steady-state state.
Queener et al. 1965
Transient
stage
V = total wear
β, n = constants
x = slip distance
K = steady-state
Steady-state stage
Wear map
Ductile
Brittle
Ductile regime:
High velocity and
high normal stress =
Low wear-rate, low
friction, and shiny,
hard surface.
Transition
Friction map
Conclusions
Experimental faults
Lower blocks of Kasota dolomite and Dover limestone samples after low-velocity
experiments. The ring areas that are covered with light colored, gouge powder are the
sliding fault slip surfaces. They are surrounded by inner and outer rings of ejected
gouge.
Dover limestone
Combined: Wear and Friction maps
Wear and Friction Maps
We found above that the wear-rate and friction depends on both slip velocity and normal stress. An effective way to present these
relations is by Wear map and Friction map (below) that are frequently used in the engineering literature to depict frictional
resistance and wear-rate behavior of materials under a wide range of loading conditions. The wear and friction maps for carbonate
rocks (below) can be used for predicting fault behavior.
Kasota dolomite
A
Thermally decomposed carbonate slip surfaces:
A below displays a transition from gouge powder (bright
yellow, P) to patches of decomposed crust (light brown,
DC) on the slip surface. Dark gray area (R) are exposed
rock surfaces. Dolomite on quartzite sample under
V = 0.14 m/s.
B below displays continuous coverage by the decomposed
shining surfaces in limestone, formed under V = 0.36 m/s.
P
Experimental settings
Thermal Correction - The displacement normal to the
slip direction (FND) is first corrected for the thermal
expansion of the sample due to frictional heating.
Fitting and differentiate – The FND signal is fitted
and differentiate to determined the wear-rate in units of:
[μm/m] - (micron of fault wear/ meter of fault slip)
Under low slip–velocity (namely: high friction and low
temperature), the slip surfaces are covered with powder (A below).
Under high slip–velocity (namely: low friction and high
temperature), the slip surfaces are covered with hard, dark and
shinny crust (Siman-Tov et al., in pre). These surfaces were
probably created by thermal decomposition (Han et al, 2007).
A
Archard’s wear equation - Archard (1953) wear equation states that
total wear is linearly related to slip distance and normal stress.
The main objectives:
A. Determine the effects of normal stress and slip velocity on wear-rate;
B. Investigate the relations between wear-rate and frictional strength.
Wear-rate calculations
Wear-rate [mm/m]
Under Low velocity :
Wear-rates depend on normal stress
Wear-rate [mm/m]
The two graphs on the right display wear-rates
as function of slip velocity. They indicate:
Slip along faults is always associated with frictional resistance and
surface wear. The dominant factors that control friction and wear are:
rock composition (lithology, grain size, mineral hardness),
environmental conditions (fluids chemistry/pressure, humidity,
temperature), fault-zone conditions (roughness, hardness, gouge
thickness, gouge grain size), and mechanical loading (normal stress,
slip velocity, pore pressure).
Rotary shear apparatus at Oklahoma University
(Reches & Lockner (2010).
The experiment configuration (left) includes: an
Upper block (UB) with a ring-shaped contact
sliding on a flat, lower block (LB). Two metal
disks, which are fixed on each block, host eddy
currents sensors (in green) that measure the fault
normal displacement (FND). Thermocouples
(TC) are embedded in the upper block ~ 3 mm
from the slip surface. We continuously monitored:
shear and normal stress, velocity and FND
Observations: Fault slip surfaces
Observations: Wear–rates and Friction coefficients
Motivation: Friction and wear relations
Non-linear Coulomb friction
In an ideal Coulomb material, the shear stress
is a linear function of the normal stress.
We observed however (left), that
 = 𝒂𝒏 𝒃
where a and b are constants, and where b is a
function of slip velocity (right).
These relations indicate more ductile behavior
at high velocities.
• Two regimes of wear-friction-fault morphology in experimental carbonate faults:
• Brittle regime
• Conditions: Low velocity and high normal stress
• Fault properties: High wear-rate, high friction (m > 0.7) , gouge covered surface
• Deformation mechanism: asperity fracture, three-body shear
• Ductile regime
• Conditions: High velocity (seismic) and high normal stress
• Fault properties: Low wear-rate, low friction ( m < 0.5), shining-hard surface
• Deformation mechanism: plastic flow, thermal decomposition
- Arachard, J. F., 1953. Contact rubbing of flat surfaces. Journal of Applied Physics, v. 24, 8, p. 981-988.
- Boneh, Y., 2012. Wear and gouge along faults: Experimental and mechanical analysis. MS Thesis, U of Oklahoma.
- Han, R. et al., 2007, Ultralow friction of carbonate faults caused by thermal decomposition: Science, v. 316.
- Queener, C.A., et al., 1965, Transient wear of machine parts: Wear, v. 8, p. 391-400.
- Siman-Tov et al., in prep.