Slip Velocity

The node facilitates a simplified form of slip friction modeling, which can be used in the case that the direction and speed of the sliding is known. In this case, there is no need to solve for the friction forces and slip orientation.

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

The and Friction nodes are mutually exclusive.

The node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

The slip velocity is defined as acting in the tangent plane of the destination boundary, and is given along the directions of a boundary system.

Only boundary systems can be selected. Make sure that the tangents of the selected boundary system are well defined on all destination boundaries.

Select a — , , or . Since the velocity is prescribed, a velocity dependent friction model can be used also in a stationary analysis.

For friction, enter the μ.

For friction, enter a μstat, a μdyn and a αdcf.

The effective friction coefficient is

where vslip is the slip velocity.

For both Coulomb type models, you can modify the rules for sliding by providing minimum and maximum shear tractions.

Enter a Tcohe to provide an offset to the tangential traction.

Independently, you can enter a Tt,max. This is the maximum tangential traction, independent of the contact pressure. The default expression is Inf, indicating that no limit on the tangential traction is active.

The magnitude of the tangential friction traction, Tt,crit, can be written as

Here, Tn is the contact pressure.

When is set to , enter an expression to define Tt,crit. This expression can depend on any quantity. However, the implementation of the friction model is only correct if Tt,crit does not depend implicitly on the current friction force.

Enter the relative velocity between the destination and source boundaries, vslip. The velocity is expressed in the coordinate system provided in the section, interpreted on the destination boundary.

To display this section, click the button (

) and select in the 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 — or . For , enter an absolute value for the Δfriction, which is the gap when the friction becomes active.

Select to compute and store to the energy dissipated by friction. This adds one extra set of state variables to be stored. The integration is explicit, and adds only marginally to the computational cost.

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

Physics tab with selected in the Model Builder tree: