By adding the Friction subnode to a Contact node, you can model static and dynamic friction.

The selection in the Friction node is the same as that of its parent Contact node. There can only be one Friction node under a specific Contact node.

If Friction and Adhesion are present under the same Contact node, the friction settings will be ignored at the locations where the adhesion criterion is fulfilled.

Select a Friction model — Coulomb or Exponential dynamic Coulomb. The latter can only be used in a time dependent analysis, since the value of the frictional coefficient depends on the slip velocity.

For Coulomb friction, enter the Friction coefficient μ.

For Exponential dynamic Coulomb friction, enter the Static friction coefficient μstat, the Dynamic friction coefficient μdyn and the Friction decay coefficient αdcf.

where vs is the slip velocity.

Enter the Cohesion sliding resistance Tcohe to set a tangential traction that must be overcome before sliding can occur.

Independently, you can enter a Maximum tangential traction Tt,max. When the tangential traction exceeds this value, slip will occur, independent of the normal pressure. The default expression is Inf, indicating that no limit on the tangential traction is active.

If Formulation is Penalty in the parent Contact node, select the Penalty factor control — From Parent or User defined. When From Parent, the tangential penalty factor pt = pn/3. For User defined, enter the Tangential force penalty factor pt. The default value is (<phys>.<contact_tag>.E_char/<phys>.hmin_dst)/3.

If Formulation is Augmented Lagrangian in the parent Contact node, enter values or expressions for the components of the initial force acting on the destination surface as Friction force Tt.

To determine whether friction effects are active when starting the solution or not, select the Previous contact state — Not in contact or In contact.

For In contact enter values or expressions for the Previous mapped source coordinates xm, old. These serve as initial values to compute the tangential slip. The default value is (X, Y, Z) and indicates that the contacting boundaries are perfectly coincident in the initial state. The mapped source coordinates are defined as the location on the source boundary where it is hit by a certain point on the destination boundary.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.

For numerical reasons, the gap value will not be exactly zero even when the boundaries are in contact. A certain small positive value of the gap must thus be used to determine that the boundaries touch each other, so that friction forces can be introduced. Select a Friction detection — Automatic or Manual. For Manual, enter an absolute value for the Friction detection tolerance Δfriction, which is the gap when the friction becomes active.

Select Compute frictional dissipation energy to compute and store to the energy dissipated by friction. This adds one extra scalar field and an extra distributed ODE.

You can also request that the total accumulated slip distance it stored by selecting the Store accumulated slip check box.

Physics tab with Contact selected in the Model Builder tree: