Civil Engineering Reference
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µ
(constant friction coefficient)
Contact pressure
Figure 5.14 The basic Coulomb friction model as given in ABAQUS [1.29].
to the contact pressure between the contacting bodies. In the basic form of
the Coulomb friction model, two contacting surfaces can carry shear stresses
up to a certain magnitude across their interface before they start sliding
relative to one another; this state is known as sticking. The Coulomb
friction model defines this critical shear stress,
t
crit
, at which sliding of the
surfaces starts as a fraction of the contact pressure,
p
, between the surfaces
(
t
crit
¼mp
). The stick/slip calculations determine when a point transitions
from sticking to slipping or from slipping to sticking. The fraction,
m
,is
known as the coefficient of friction. For the case when the slave surface
consists of a node-based surface, the contact pressure is equal to the normal
contact force divided by the cross-sectional area at the contact node. In
ABAQUS [1.29], the default cross-sectional area is 1.0, and modelers can
specify a cross-sectional area associated with every node in the node-based
surface when the surface is defined or, alternatively, assign the same area to
every node through the contact property definition. The basic friction
model assumes that it is the same in all directions (isotropic friction).
For a 3D simulation, there are two orthogonal components of shear stress
along the interface between the two bodies. These components act in the
slip directions for the contact surfaces or contact elements.
There are two ways to define the basic Coulomb friction model in ABA-
QUS [1.29]. In the default model, the friction coefficient is defined as a
function of the equivalent slip rate and contact pressure. The coefficient
of friction can be set to any nonnegative value. A zero friction coefficient
means that no shear forces will develop and the contact surfaces are free
to slide. You do not need to define a friction model for such a case.
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