COMSOL 6.4 - Friction (General Contact)

By adding the subnode to a Contact Model node, you can include static and dynamic friction to the contact problem.

The friction forces are defined as boundary tractions with respect to the selected coordinate system. The selection is limited to boundary systems.

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

Friction Parameters

Select a — or . The option is only relevant for time-dependent studies, since the value of the friction coefficient depends on the slip velocity.

For friction, enter a 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 options, you can modify the rules for sliding by providing minimum and maximum shear tractions.

Enter a Tcohe to set a tangential traction that must be overcome before sliding can occur. The use of cohesion will give an offset to the friction force under sliding conditions.

Independently, you can enter a 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.

The tangential friction force during sliding, Tt,crit, can be written as

Here, Tn is the contact pressure. If the tangential force is less than this value, there is no sliding.


	A general contact problem can involve the interaction between many different materials where each interaction might require different friction parameters. For such situations, the friction parameters can be made dependent on the mapping by using the src2dst operator combined with, for example, the if or nif operators. The expression if((src2dst_p1(dom)==2 && dom==3) \|\| (src2dst_p1(dom)==3 && dom==2), 0.7, 0.3) for the friction coefficient μ implies that μ = 0.7 if the contact mapping occurs between boundaries 2 and 3, otherwise μ = 0.3.


	For an example of a conditionally defined friction parameters, see Objects Falling in a Box: Application Library path Structural_Mechanics_Module/Contact_and_Friction/falling_objects

Advanced

To display this section, click the button (

) and select in the dialog.

For numerical reasons, the gap value is not exactly zero even when the boundaries are in contact. A small positive gap value must thus be used to determine that the boundaries are in contact, and to introduce friction forces. Select a — or . For , enter an absolute value for the Δfriction, which defines the gap distance when friction is activated.

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