Finite Element Analysis of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 494

Experimental data show that the friction coefficient that opposes the
initiation of slipping from a sticking condition is different from the friction
coefficient that opposes established slipping. The former is typically referred
to as the “static” friction coefficient, and the latter is referred to as the
“kinetic” friction coefficient. Typically, the static friction coefficient is
higher than the kinetic friction coefficient. In the default model, the static
friction coefficient corresponds to the value given at zero slip rate, and the
kinetic friction coefficient corresponds to the value given at the highest slip
rate. The transition between static friction and kinetic friction is defined by
the values given at intermediate slip rates. In this model, the static and kinetic
friction coefficients can be functions of contact pressure, temperature, and
field variables. ABAQUS [1.29] also provides a model to specify a static fric-
tion coefficient and a kinetic friction coefficient directly. In this model, it is
assumed that the friction coefficient decays exponentially from the static
value to the kinetic value according to a formula given in the software. Mod-
elers can specify an optional equivalent shear stress limit, t max , so that,
regardless of the magnitude of the contact pressure stress, sliding will occur
if the magnitude of the equivalent shear stress reaches this value; see
Figure 5.15 . A value of zero is not allowed. This shear stress limit is typically
introduced in cases when the contact pressure stress may become very large
(as can happen in some manufacturing processes), causing the Coulomb the-
ory to provide a critical shear stress at the interface that exceeds the yield
stress in the material beneath the contact surface. A reasonable upper bound

Critical shear stress in model with τ max limit

µ (constant friction coefficient)

Contact pressure

Figure 5.15 Friction model with a limit on the critical shear stress as given in ABAQUS
[1.29].